dependent variable in harlow's experiment

Harlow’s Monkey Experiments: 3 Findings About Attachment

When that need is met, the infant develops a secure attachment style; however, when that need is not met, the infant can develop an attachment disorder.

In this post, we’ll briefly explore attachment theory by looking at Harlow’s monkey experiments and how those findings relate to human behavior and attachment styles. We’ll also look at some of the broader research that resulted from Harlow’s experiments.

Before we begin, I have to warn you that Harlow’s experiments are distressing and can be upsetting. Nowadays, his experiments are considered unethical and would most likely not satisfy the requirements of an ethical board. However, knowing this, the findings of his research do provide insight into the important mammalian bond that exists between infant and parent.

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This Article Contains:

Harlow’s experiments: a brief summary, three fascinating findings & their implications, its connection to love and attachment theory, follow-up and related experiments, criticisms of harlow’s experiments, ethical considerations of harlow’s experiments, relevant positivepsychology.com resources, a take-home message.

Harry Harlow was trained as a psychologist, and in 1930 he was employed at the University of Wisconsin–Madison. His areas of expertise were in infant–caregiver relationships, infant dependency and infant needs, and social deprivation and isolation. He is also well known for his research using rhesus monkeys.

Maternal surrogates: Food versus comfort

For his experiments, Harlow (1958) separated infant rhesus monkeys from their mothers. He then constructed two surrogate ‘mothers’ for the infants: one surrogate made out of metal but that provided milk through an artificial nipple, the other surrogate covered in soft, fluffy material but that didn’t offer food.

The first surrogate delivered food but provided no comfort; the second did not deliver food, but the rhesus infants were able to cuddle with it.

When both surrogates were placed in the infants’ cages, Harlow found the surrogates satisfied different needs of the rhesus infants. The wire surrogate satisfied the infants’ primary need for food. However, when Harlow made a loud noise to frighten the rhesus infants, they ran to the second, fluffy surrogate for comfort.

Maternal surrogates: A secure base from which to explore

In subsequent experiments, Harlow (1958) showed that the fluffy surrogate acted as a secure base from which rhesus infants could explore an unfamiliar environment or objects. In these experiments, the infants, along with their fluffy surrogates, were placed in an unfamiliar environment like a new cage.

These infants would explore the environment and return to the surrogate for comfort if startled. In contrast, when the infants were placed in the new environment without a surrogate, they would not explore but rather lie on the floor, paralyzed, rocking back and forth, sucking their thumbs.

The absence of a maternal surrogate

Harlow also studied the development of rhesus monkeys that were not exposed to a fluffy surrogate or had no surrogate at all. The outcome for these infants was extremely negative. Rhesus infants raised with a milk-supplying metal surrogate had softer feces than infants raised with a milk-supplying fluffy surrogate.

Harlow posited that the infants with the metal surrogates suffered from psychological disturbances, which manifested in digestive problems.

Rhesus infants raised with no surrogates showed the same fearful behavior when placed in an unfamiliar environment as described above, except that their behavior persisted even when a surrogate was placed in the environment with them. They also demonstrated less exploratory behavior and less curiosity than infants raised with surrogates from a younger age.

When these infants were approximately a year old, they were introduced to a surrogate. In response, they behaved fearfully and violently. They would rock continuously, scream, and attempt to escape their cages. Fortunately, these behaviors dissipated after a few days. The infants approached, explored, and clung to the surrogate, but never to the same extent as infants raised with a fluffy surrogate from a younger age.

Primary drives are ones that ensure a creature’s survival, such as the need for food or water. Harlow suggests that there is another drive, ‘contact comfort,’ which the fluffy surrogate satisfied.

The ‘contact comfort’ drive does more than just satisfy a need for love and comfort. From Harlow’s experiments, it seems that these fluffy surrogates offered a secure, comforting base from which infants felt confident enough to explore unfamiliar environments and objects, and to cope with scary sounds.

Conclusions from Harlow’s work were limited to the role of maternal surrogates because the surrogates also provided milk – a function that only female mammals can perform. Consequently, it was posited that human infants have a strong need to form an attachment to a maternal caregiver (Bowlby, 1951). However, subsequent research has shown that human infants do not only form an attachment with:

• a female caregiver,
• a caregiver that produces milk, or
• one caregiver (Schaffer & Emerson, 1964).

The bond between human infant and caregiver is not limited to only mothers, but can extend to anyone who spends time with the infant. Schaffer and Emerson (1964) studied the emotional responses of 60 infants to better understand their attachments and behaviors.

They found that at the start of the study, most of the infants had formed an attachment with a single person, normally the mother (71%), and that just over a third of the infants had formed attachments to multiple people, sometimes over five.

However, when the infants were 18 months, only 13% had an attachment to a single person, and most of the infants had two or more attachments. The other people with whom infants formed an attachment included:

• Grandparents
• Siblings and family members
• People who were not part of their family, including neighbors or other children

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Harlow’s experiment on rhesus monkeys shed light on the importance of the relationship between caregiver and infant. This relationship satisfies other needs besides food and thirst, and the behavior of rhesus infants differs depending on whether they were raised (1) with or without a surrogate and (2) whether that surrogate was a fluffy (i.e., comforting) or metal (i.e., non-comforting) one.

Widespread thinking at the time was that children only needed their physical needs to be satisfied in order to grow up into healthy, well-adjusted adults (Bowlby, 1951, 1958). Harlow’s work, however, suggests that the caregiver satisfies another need of the infant: the need for love.

It is difficult to know whether the infant monkeys truly loved the surrogate mothers because Harlow could not ask them directly or measure the feeling of love using equipment.

But there is no doubt that the presence (or absence) of a surrogate mother deeply affected the behavior of the infant monkeys, and monkeys with surrogate mothers displayed more normal behavior than those without.

Additionally, Harlow’s work also showed that infant monkeys looked for comfort in the fluffy surrogate mother, even if that surrogate mother never provided food.

From this research, we can conclude that infants feel an attachment toward their caregiver. That attachment is experienced as what we know to be ‘love.’ This attachment seems to be important for a variety of reasons, such as:

• Feeling safe when afraid or in an unfamiliar environment
• Responding in a loving, comforting way to the needs and feelings of infants

The infant’s need to form an attachment was not considered a primary need until 1952, when Bowlby argued that this basic need was one that infants feel instinctually (Bowlby & World Health Organization, 1952).

Bowlby’s work formed the basis of attachment theory – the theory that the relationship between infant and caregiver affects the infant’s psychological development.

The contributions from these researchers include:

• The emotional needs of infants are critical to healthy development and survival
• Parents play an important role besides merely satisfying the physical needs of an infant to ensure survival

Maternal deprivation

John Bowlby (1958) argued that maternal deprivation has extremely negative effects on the psychological and emotional development of children.

He was especially interested in extreme forms of parental deprivation, such as children who were homeless, abandoned, or institutionalized and therefore had no contact with their parents.

From his research, Bowlby argued that satisfying the physiological needs of the child did not ensure healthy development and that the effects of maternal deprivation were grave and difficult to reverse.

Specifically, he argued that how the caregiver behaves in response to the behavior and feelings of an infant plays an important role in infants’ psychological and emotional development (Bowlby, 1958).

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Attachment styles in infants

How the caregiver responds to the infant is known as sensitive responsiveness (Ainsworth et al., 1978). The fluffy surrogate mothers in Harlow’s experiment were not responsive, obviously; however, their presence, the material used to cover them, and their shape allowed the rhesus infants to cling to them, providing comfort, albeit a basic, unresponsive one.

The findings from research by Harlow and Bowlby led to pioneering work by Mary Ainsworth on infant–mother attachments and attachment theory in infants. Specifically, she developed an alternative method to study child–parent attachments, using the ‘strange situation procedure’:

• The parent and child are placed together in an unfamiliar room.
• At some point, a (female) stranger enters the room, chats to the parent and plays with/chats to the infant.
• The parent leaves the room, and the child and stranger are alone together.
• The parent returns to the room, and the stranger leaves. The parent chats and plays with the child.
• The parent leaves the room, and the child is alone.
• The stranger returns and tries to chat and play with the child.

Depending on how the child behaved at the separation and introduction of the parent and the stranger, respectively, the attachment style between the infant and mother was classified as either secure, anxious-avoidant, or anxious-resistant.

For more reading on Mary Ainsworth, Harlow, and Bowlby, you can find out more about their work in our What is Attachment Theory? article.

Harlow’s studies on dependency in monkeys – Michael Baker

Subsequent research has questioned some of Harlow’s original findings and theories (Rutter, 1979). Some of these criticisms include:

• Harlow’s emphasis on the importance of a single, maternal figure in the child–parent relationship. As mentioned earlier, children can develop important relationships with different caregivers who do not need to be female/maternal figures (Schaffer & Emerson, 1964).
• The difference between a bond and an attachment. Children can form attachments without forming bonds. For example, a child might follow a teacher (i.e., an example of attachment behavior) and yet not have any deep bonds or relationships with other children. This suggests that these two types of relationships might be slightly different or governed by different processes.
• Other factors can also influence the relationship between child and parent, and their attachment. One such factor is the temperament of the parent or the child (Sroufe, 1985). For example, an anxious parent or child might show behavior that suggests an insecure attachment style.  Another factor is that behaviors that suggest attachment do not necessarily mean that the parent is better responding to the child’s needs. For example, children are more likely to follow a parent when in an unfamiliar environment. This behavior does not automatically imply that the child’s behavior is a result of the way the parent has responded in the past; instead, this is just how children behave.

One of Harlow’s most controversial claims was that peers were an adequate substitute for maternal figures. Specifically, he argued that monkeys that were raised with other similarly aged monkeys behaved the same as monkeys that were raised with their parents. In other words, the relationship with a parent is not unique, and peers can meet these ‘parental’ needs.

However, subsequent research showed that rhesus monkeys raised with peers were shyer, explored less, and occupied lower roles in monkey hierarchies (Suomi, 2008; Bastian, Sponberg, Suomi, & Higley, 2002).

Importantly, Harlow’s experiments are not evidence that there should be no separation between parent and infant. Such a scenario would be almost impossible in a normal environment today. Frequent separations between parent and infant are normal; however, it is critical that the infant can re-establish contact with the parent.

If contact is successfully re-established, then the bond between parent and child is reinforced.

Impact on psychological theories about human behavior

Harlow’s research on rhesus monkeys demonstrated the important role that parents have in our development and that humans have other salient needs that must be met to achieve happiness.

Harlow’s work added weight to the arguments put forward by Sigmund Freud (2003) that our relationship with our parents can affect our psychological development and behavior later in our lives.

Harlow’s work also influenced research on human needs. For example, Maslow (1943) argued that humans have a hierarchy of needs that must be met in order to experience life satisfaction  and happiness.

The first tier comprises physiological needs, such as hunger and thirst, followed by the second tier of needs such as having a secure place to live. The third tier describes feelings of love and belonging, such as having emotional bonds with other people. Maslow argued that self-actualization could only be reached when all of our needs were met.

Harlow continued to perform experiments on rhesus monkeys, including studying the effects of partial to complete social deprivation. It is highly unlikely that Harlow’s experiments would pass the rigorous requirements of any ethics committee today. The separation of an infant from their parent, especially intending to study the effect of this separation, would be considered cruel.

Kobak (2012) outlines the experiments performed by Harlow, and it is immediately obvious that many of these animals experienced severe emotional distress because of their living conditions.

In the partial isolation experiments, Harlow isolated a group of 56 monkeys from other monkeys; although they could hear and see the other monkeys, they were prevented from interacting with or touching them. These monkeys developed aggressive and severely disturbed behavior, such as staring into space, repetitive behaviors, and self-harm through chewing and tearing at their flesh.

Furthermore, the monkeys that were raised in isolation did not display normal mating behavior and failed in mating.

The complete social deprivation experiments were especially cruel. In these experiments, they raised the monkeys in a box, alone, with no sensory contact with other monkeys. They never saw, heard, or came into contact with any other monkeys.

The only contact that they had was with a human experimenter, but this was through a one-way screen and remote control; there was no visual input of another living creature.

Harlow described this experience as the ‘pit of despair.’ Monkeys raised in this condition for two years showed severely disturbed behavior, unable to interact with other monkeys, and efforts to reverse the effect of two years in isolation were unsuccessful.

Harlow considered this experiment as an analogy of what happens to children completely deprived of any social contact for the first few years of their lives.

The effects of Harlow’s experiments were not limited to only one generation of monkeys. In one of his studies, a set of rhesus monkeys raised with surrogates, rather than their own mothers, gave birth to their own infants.

Harlow observed that these parent-monkeys, which he termed ‘motherless monkeys,’ were dysfunctional parents. They either ignored their offspring or were extremely aggressive toward them. They raised two generations of monkeys to test the effect of parental deprivation.

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Harlow’s monkey experiments were cruel, but it would have been impossible to conduct the same experiments using human infants.

Furthermore, Harlow’s experiments helped shift attention to the important role that caregivers provide for children.

When Harlow was publishing his research, the medical fraternity believed that meeting the physical needs of children was enough to ensure a healthy child. In other words, if the child is fed, has water, and is kept warm and clean, then the child will develop into a healthy adult.

Harlow’s experiments showed that this advice was not true and that the emotional needs of infants are critical to healthy development.

With love, affection, and comfort, infants can develop into healthy adults.

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• Ainsworth, M. D. S., Blehar, M. C., Waters, E., & Wall, S. (1978). Patterns of attachment: A psychological study of the strange situation . Erlbaum.
• Bastian, M. L., Sponberg, A. C., Suomi, S. J., & Higley, J. D. (2002). Long-term effects of infant rearing condition on the acquisition of dominance rank in juvenile and adult rhesus macaques (Macaca mulatta). Developmental Psychobiology , 42 , 44–51.
• Bowlby, J. (1951). Maternal care and mental health . Columbia University Press.
• Bowlby, J. (1958). The nature of the child’s tie to his mother. International Journal of Psycho-Analysis , 39 , 350–373.
• Bowlby, J., & World Health Organization. (1952). Maternal care and mental health: A report prepared on behalf of the World Health Organization as a contribution to the United Nations programme for the welfare of homeless children . World Health Organization.
• Colman, M. A. (2001). Oxford dictionary of psychology . Oxford University Press.
• Freud, S. (2003). An outline of psychoanalysis . Penguin UK.
• Harlow, H. F. (1958). The nature of love. American Psychologist , 13 (12), 673.
• Kobak, R. (2012). Attachment and early social deprivation: Revisiting Harlow’s monkey studies. Developmental psychology: Revisiting the classic studies , S , 10–23.
• Maslow, A. H. (1943). A theory of human motivation. Psychological Review , 50 (4), 370–96.
• Rutter, M. (1979). Maternal deprivation, 1972–1978: New findings, new concepts, new approaches. Child Development , 50 (2), 283–305.
• Schaffer, H. R., & Emerson, P. E. (1964). The development of social attachments in infancy. Monographs of the Society for Research in Child Development , 29 (3), 1–77.
• Sroufe, L. A. (1985). Attachment classification from the perspective of infant-caregiver relationships and infant temperament. Child Development , 56 (1), 1–14.
• Suomi, S. J. (2008). Attachment in rhesus monkeys. In J. Cassidy & P. Shaver (Eds.), Handbook of attachment: Theory, research and clinical applications (pp. 173–191). Guilford Press.

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Parental attunement and attention also shape the architecture of the brain and the function of the nervous system. When a child does not encounter sufficient parental attunement, compassion, kindness, and empathy, they are deprived of experiences that foster the integration of the brain. This results in a dysregulated nervous system, which cannot produce regulated emotions, thoughts, behaviors, relationships, or bodily systems. The impeded integration causes internal distress, the symptoms of which include chronic illness, recurrent pain, poor relationships, and “mental health” conditions (which are health conditions).

The child (and subsequently insufficiently supported adult) tries to find relief through whatever means are available: numbing, acting out, withdrawing, overeating, substance abuse, dissociation, splitting, self-harm, etc. These are not “disorders” but *survival adaptations* demanded by the unsafe environment. The child/adult uses whatever survival adaptations are available; when they have better options, they use them.

When the dysregulated person receives sufficient psychosocial support, such as through truly therapeutic or other integrative relationships, the brain can integrate and the nervous system can regulate. People, like animals and plants, flourish in supportive environments. Fix the environment and the symptoms fade.

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Harry Harlow Theory & Rhesus Monkey Experiments in Psychology

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Harlow (1958 wanted to study the mechanisms by which newborn rhesus monkeys bond with their mothers.

These infants depended highly on their mothers for nutrition, protection, comfort, and socialization.  What, exactly, though, was the basis of the bond?

The learning theory of attachment suggests that an infant would form an attachment with a carer who provides food. In contrast, Harlow explained that attachment develops due to the mother providing “tactile comfort,” suggesting that infants have an innate (biological) need to touch and cling to something for emotional comfort.

Harry Harlow did a number of studies on attachment in rhesus monkeys during the 1950’s and 1960″s.  His experiments took several forms:

Cloth Mother vs. Wire Mother Experiment

Experiment 1.

Harlow (1958) separated infant monkeys from their mothers immediately after birth and placed in cages with access to two surrogate mothers, one made of wire and one covered in soft terry toweling cloth.

In the first group, the terrycloth mother provided no food, while the wire mother did, in the form of an attached baby bottle containing milk.

Both groups of monkeys spent more time with the cloth mother (even if she had no milk).  The infant would only go to the wire mother when hungry. Once fed it would return to the cloth mother for most of the day.  If a frightening object was placed in the cage the infant took refuge with the cloth mother (its safe base).

This surrogate was more effective in decreasing the youngster’s fear.  The infant would explore more when the cloth mother was present.

This supports the evolutionary theory of attachment , in that the sensitive response and security of the caregiver are important (as opposed to the provision of food).

Experiment 2

Harlow (1958) modified his experiment and separated the infants into two groups: the terrycloth mother which provided no food, or the wire mother which did.

All the monkeys drank equal amounts and grew physically at the same rate. But the similarities ended there. Monkeys who had soft, tactile contact with their terry cloth mothers behaved quite differently than monkeys whose mothers were made out of hard wire.

The behavioral differences that Harlow observed between the monkeys who had grown up with surrogate mothers and those with normal mothers were;

• They were much more timid.
• They didn’t know how to act with other monkeys.
• They were easily bullied and wouldn’t stand up for themselves.
• They had difficulty with mating.
• The females were inadequate mothers.

These behaviors were observed only in the monkeys left with the surrogate mothers for more than 90 days.

For those left less than 90 days, the effects could be reversed if placed in a normal environment where they could form attachments.

Rhesus Monkeys Reared in Isolation

Harlow (1965) took babies and isolated them from birth. They had no contact with each other or anybody else.

He kept some this way for three months, some for six, some for nine and some for the first year of their lives. He then put them back with other monkeys to see what effect their failure to form attachment had on behavior.

The results showed the monkeys engaged in bizarre behavior, such as clutching their own bodies and rocking compulsively. They were then placed back in the company of other monkeys.

To start with the babies were scared of the other monkeys, and then became very aggressive towards them. They were also unable to communicate or socialize with other monkeys. The other monkeys bullied them. They indulged in self-mutilation, tearing hair out, scratching, and biting their own arms and legs.<!–

In addition, Harlow created a state of anxiety in female monkeys which had implications once they became parents. Such monkeys became so neurotic that they smashed their infant’s face into the floor and rubbed it back and forth.

Harlow concluded that privation (i.e., never forming an attachment bond) is permanently damaging (to monkeys).

The extent of the abnormal behavior reflected the length of the isolation. Those kept in isolation for three months were the least affected, but those in isolation for a year never recovered from the effects of privation.

Conclusions

Studies of monkeys raised with artificial mothers suggest that mother-infant emotional bonds result primarily from mothers providing infants with comfort and tactile contact, rather than just fulfilling basic needs like food.

Harlow concluded that for a monkey to develop normally s/he must have some interaction with an object to which they can cling during the first months of life (critical period).

Clinging is a natural response – in times of stress the monkey runs to the object to which it normally clings as if the clinging decreases the stress.

He also concluded that early maternal deprivation leads to emotional damage but that its impact could be reversed in monkeys if an attachment was made before the end of the critical period .

However, if maternal deprivation lasted after the end of the critical period, then no amount of exposure to mothers or peers could alter the emotional damage that had already occurred.

Harlow found, therefore, that it was social deprivation rather than maternal deprivation that the young monkeys were suffering from.

When he brought some other infant monkeys up on their own, but with 20 minutes a day in a playroom with three other monkeys, he found they grew up to be quite normal emotionally and socially.

The Impact of Harlow’s Research

Harlow’s research has helped social workers to understand risk factors in child neglect and abuse such as a lack of comfort (and so intervene to prevent it).

Using animals to study attachment can benefit children who are most at risk in society and can also have later economic implications, as those children are more likely to grow up to be productive members of society.

Ethics of Harlow’s Study

Harlow’s work has been criticized.  His experiments have been seen as unnecessarily cruel (unethical) and of limited value in attempting to understand the effects of deprivation on human infants.

It was clear that the monkeys in this study suffered from emotional harm from being reared in isolation.  This was evident when the monkeys were placed with a normal monkey (reared by a mother), they sat huddled in a corner in a state of persistent fear and depression.

Harlow’s experiment is sometimes justified as providing a valuable insight into the development of attachment and social behavior. At the time of the research, there was a dominant belief that attachment was related to physical (i.e., food) rather than emotional care.

It could be argued that the benefits of the research outweigh the costs (the suffering of the animals).  For example, the research influenced the theoretical work of John Bowlby , the most important psychologist in attachment theory.

It could also be seen as vital in convincing people about the importance of emotional care in hospitals, children’s homes, and daycare.

Harlow, H. F., Dodsworth, R. O., & Harlow, M. K. (1965). Total social isolation in monkeys . Proceedings of the National Academy of Sciences of the United States of America, 54 (1), 90.

Harlow, H. F. & Zimmermann, R. R. (1958). The development of affective responsiveness in infant monkeys . Proceedings of the American Philosophical Society, 102 ,501 -509.

Harlow’s Classic Studies Revealed the Importance of Maternal Contact

• Child Development
• Cognitive Psychology
• Infant Development
• Social Interaction
• Social Isolation
• Social Psychology

Harry Harlow’s empirical work with primates is now considered a “classic” in behavioral science, revolutionizing our understanding of the role that social relationships play in early development. In the 1950s and 60s, psychological research in the United States was dominated by behaviorists and psychoanalysts, who supported the view that babies became attached to their mothers because they provided food. Harlow and other social and cognitive psychologists argued that this perspective overlooked the importance of comfort, companionship, and love in promoting healthy development.

Using methods of isolation and maternal deprivation, Harlow showed the impact of contact comfort on primate development. Infant rhesus monkeys were taken away from their mothers and raised in a laboratory setting, with some infants placed in separate cages away from peers. In social isolation, the monkeys showed disturbed behavior, staring blankly, circling their cages, and engaging in self-mutilation. When the isolated infants were re-introduced to the group, they were unsure of how to interact — many stayed separate from the group, and some even died after refusing to eat.

Even without complete isolation, the infant monkeys raised without mothers developed social deficits, showing reclusive tendencies and clinging to their cloth diapers. Harlow was interested in the infants’ attachment to the cloth diapers, speculating that the soft material may simulate the comfort provided by a mother’s touch. Based on this observation, Harlow designed his now-famous surrogate mother experiment.

In this study, Harlow took infant monkeys from their biological mothers and gave them two inanimate surrogate mothers: one was a simple construction of wire and wood, and the second was covered in foam rubber and soft terry cloth. The infants were assigned to one of two conditions. In the first, the wire mother had a milk bottle and the cloth mother did not; in the second, the cloth mother had the food while the wire mother had none.

In both conditions, Harlow found that the infant monkeys spent significantly more time with the terry cloth mother than they did with the wire mother. When only the wire mother had food, the babies came to the wire mother to feed and immediately returned to cling to the cloth surrogate.

Harlow’s work showed that infants also turned to inanimate surrogate mothers for comfort when they were faced with new and scary situations. When placed in a novel environment with a surrogate mother, infant monkeys would explore the area, run back to the surrogate mother when startled, and then venture out to explore again. Without a surrogate mother, the infants were paralyzed with fear, huddled in a ball sucking their thumbs. If an alarming noise-making toy was placed in the cage, an infant with a surrogate mother present would explore and attack the toy; without a surrogate mother, the infant would cower in fear.

Together, these studies produced groundbreaking empirical evidence for the primacy of the parent-child attachment relationship and the importance of maternal touch in infant development. More than 70 years later, Harlow’s discoveries continue to inform the scientific understanding of the fundamental building blocks of human behavior.

Harlow H. F., Dodsworth R. O., & Harlow M. K. (1965). Total social isolation in monkeys. Proceedings of the National Academy of Sciences of the United States of America. Retrieved from https://www.ncbi.nlm.nih.gov/pmc/articles/PMC285801/pdf/pnas00159-0105.pdf

Suomi, S. J., & Leroy, H. A. (1982). In memoriam: Harry F. Harlow (1905–1981). American Journal of Primatology, 2 , 319–342. doi:10.1002/ajp.1350020402

Tavris, C. A. (2014). Teaching contentious classics. The Association for Psychological Science . Retrieved from https://www.psychologicalscience.org/observer/teaching-contentious-classics

Loved the simplicity of article but wanted to Apa cite it but didn’t see a name who wrote it

typed a partial comment and was disrupted and never got around to sending it. I tried to relocate it on my computer, but was not able. Could have been my thoughts. As a substitute teacher I see the results of giving a child a phone rather than giving a child love and all that goes with it. I see the predictions of Harry Harlow have come to pass. No absolutes, no positive examples, no investment of time, just looking for the allusive moment of quality time, that requires an investment TIME to be there for that moment in time. Any way I’m probably not the one you’re looking for.

The above summary fails to address any critique of Harlow’s legacy. Nothing about use of Harlow’s “pit of despair,” or his “rape rack” to use his own term? Nothing about beginning “his harsher isolation and depression experiments while “corrosively depressed” and “stumbling around drunk”? No concern about any possibility of sadism as “science”? No question of “how much suffering is justified by the imperatives of science”? For starters, see S. Hansen’s 11/13/2002 salon.com review of Deborah Blum’s Love at Goon Park, or the essay on Harlow in psychologist Loren Slater’s book, Opening Skinner’s Box.

Gigi, the sole reason for the experiment was not to root out sadism, it was to explain the need for attachment. Sorry about the special feelings you have for animals. It is a good point you let us see, you can now use that opportunity to show us sadism in regards to the research they made. I will search that article you point out to see what that author had to say about sadism.

I read these these experiments when they were published in the Scientific American journals.

I find he article a good review of the original work.

I worked in Harlow’s lab as as an undergraduate student in 1951/52. What I learned from this experience is the value of facts and verified statements about animal behavior. As a 20 year old kid discharged from the army, I was severely reprimanded for stating that a monkey had bit me in anger when I slapped its paw for trying to steal reasons out of lab coat. I was bitten but I invented the reason. Our work was to flesh out the phylo-genetic scale. Along with just learning studies, with white rats as well.

And what did you discover?

Wow that’s amazing you worked in the lab, I think so just starting out in psychology and my first lesson was Harlow. It’s was very interesting learning about him, my only thought was the monkeys have to admit but that was done in those days. Thanks Sue

I agree that in this day and age, we would criticize this treatment. I have no doubt much of it still goes on, people still eat animals. That was a different time, we learn from the past so that we do not repeat it. But to be angry about the past or that someone could find the good research that was deemed from it is histrionic and a waste of positive energy.

Are you people insane? “I agree that in this day and age, we would criticize this treatment” I was raised in exactly in accord with Harlow’s experiments, denied human contact almost since birth. And you APPROVE of this?! “That was a different time, we learn from the past so that we do not repeat it.” Oh, you know so little. Look up “secure confinement” and consider what children face every day of their lives.

I agree with Harry’s theory.

I also find it sadistic or at least totally lacking in sensitivity and compassion to have torn these baby monkeys from their mothers to learn what.That they prefer warmth to a hard screen even when food is involved? It is this kind of thinking that leads to the willingness of politicians to separate families, putting children in cages so that they will be less likely to come to America for help. Truly sadistic!

I think we need like a chat forum for discussion about these issues honestly. I’d love to debate about this stuff actually and am wondering whether any means is sufficient. In regards to the actual experiment, Im not going to get my beliefs on ethical treatment mixed up and it did produce significant findings. I’m more upset about the actual findings themselves. It could also be because I see some very loose correlation between them and my life unfortunately. The published paper was definitely worth the read and I wish I didn’t.

I think the whole point is that the experiments show why politicians should NOT separate families etc.. it’s difficult to prove the effects of cruelty without being cruel. The alarming thing is how little has been learned from the sacrifice. I know a young woman with learning difficulties, abandonment issues and probable RAD who is in care. She has created a fantasy world with cuddly toys. She is chastised for this by her ‘carers’ who confiscate them and make her feel guilty about her self. I am currently composing a letter for social services to intervene. I intend enclosing the above article. Everyone who works in care should be made to read it!

I studied psychology as an undergrad several years ago, and of the cognitive development experiments that made it into academic text, Harlow’s was one that has always stuck in my mind. To refer to the outcomes and substantiated findings of studies such as these, without acknowledging the cruelty perpetuated in carrying them out, might be impossible. The two go hand in hand, and that’s the point. But years later, can we say the ends justified the means? Yes…and no. Studies such as this one, were done years ago, perhaps in a time with very different regulations; however, the findings are none the less very substantial. And, I personally believe could, and should, be referred to in the training of a variety of service and caregiver professions, as this last comment suggests. There is still much to be learned in Behavioral science area of study, but as a society in need of great change as a whole, we should be working to figure out how we can capitalize on the knowledge gained from past studies such as this one…as opposed to focusing solely on the conditions in which they were done in. That’s not to allow our emotions to diminish the importance of the findings, without putting them to good use in our everyday lives. The end goal being to make a positive difference in society moving forward.

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Harlow’s Monkey Experiment – The Bond between Babies and Mothers

Harry Harlow was an American psychologist whose studies were focused on the effects of maternal separation, dependency, and social isolation on both mental and social development.

Objective of the Harlow’s Monkey Experiment

The idea came to Harlow when he was developing the Wisconsin General Testing Apparatus or the WGTA to study the mental processes of primates, which include memory, cognition and learning. As he developed his tests, he realized that the monkeys he worked with were slowly learning how to develop strategies around his tests.

Harlow had the idea that infant monkeys who are separated from their mothers at a very early age (within 90 days) can easily cope with a surrogate, because the bond with the biological mother has not yet been established. Furthermore, he also wanted to learn whether the bond is established because of pure nourishment of needs (milk), or if it involves other factors.

How did the Harlow’s Monkey Experiment work?

Results of the harlow monkey experiment.

Furthermore, the results of the second experiment showed that while the baby monkeys in both groups consumed the same amount of milk from their “mother”, the babies who grew up with the terry cloth mother exhibited emotional attachment and what is considered as normal behaviour when presented with stressful variables. Whenever they felt threatened, they would stay close to the terry cloth mother and cuddle with it until they were calm.

Significance of the Harlow’s Monkey Experiment

Moreover, it was found that the establishment of bond between baby and mother is not purely dependent on the satisfaction of one’s physiological needs (warmth, safety, food) , but also emotional (acceptance, love, affection).

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Animal Studies Of Attachment: Lorenz And Harlow

March 5, 2021 - paper 1 introductory topics in psychology | attachment.

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Animal Studies Of Attachment: Lorenz, Imprinting And The Greylag Geese (AO1, Description):

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Lorenz, animal studies of attachment:  Lorenz’s research investigates the  Evolutionary Explanation  of attachment suggesting that infants are pre-programmed to form an attachment from the second that they are born. The findings from Lorenz’s research (as outlined below) offers support for the idea that infants have an attachment gene and that they imprint on a caregiver not long after birth.

Aim:  To investigate the mechanisms of imprinting where the youngsters follow and form an attachment to the first large, moving object that they meet.

Conclusion:  Imprinting is a form of attachment, exhibited mainly by nidifugous birds (ones who have to leave the nest early), whereby close contact is kept with the first large moving object encountered.

Evaluation Of Lorenz’s Animal Study (AO3):

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(1) POINT:  A strength of Lorenz’s study is that its findings have been highly influential within the field of developmental psychology. EXAMPLE:   For example,  the fact that imprinting is seen to be irreversible (as suggested in Lorenz’s study) suggests that attachment formation is under biological control and that attachment formation happens within a specific time frame.  EVALUATION:  This is a strength because  it lead developmental psychologists (such as Bowlby) to develop well recognised theories of attachment suggesting the attachment formation takes place during a critical period and is a biological process. Such theories have been highly influential in the way child care is administered today.

(1) POINT:  A weakness of Lorenz’s study is that it can be criticised for extrapolation. EXAMPLE:  Lorenz conducted his study on imprinting on animals the greylag geese.  EVALUATION:  This is a weakness because  humans and animals (in this case, greylag geese) are physiological different .  The way a human infant develops an attachment with their primary caregiver could be very different to the way a greylag geese forms an attachment with their primary caregiver, therefore the findings  cannot be generalised.

Animal Studies Of Attachment: Harlow, (AO1, Description):

Harlow, animal studies in attachment:  Harlow was interested in the role of ‘learning’ and the formation of caregiver, infant attachments. Harlow’s research (as described below) highlights the belief that attachments are formed through the process of ‘learning’ and the importance of ‘food giving’ in attachment formation. Harlow’s research supports the  Learning Theory  of attachment.

Procedure:  Two types of surrogate mother were constructed a harsh wire mother and a soft towelling mother. 16 baby monkeys were used, 4 in each condition.

The amount of time spent with each mother was recorded, as well as feeding time was recorded. The monkeys were also frightened with loud noises to test for mother preference during times of stress.

Evaluation Of Harlow’s Animal Study (AO3):

(1) POINT:  A weakness of Harlow’s study is that it was conducted in a controlled, artificial  laboratory setting .  EXAMPLE:  the highly controlled laboratory setting that Harlow used is not reflective of the real life situations and may cause the monkeys to behave in an artificial manner.  EVALUATION:  This is a weakness because  it means that Harlow wasn’t necessarily measuring the real-life attachment formation and therefore the study can be criticised for  lacking ecological validity.

 (2)  POINT:  Another weakness of Harlow’s study is that it can be seen to be  unethical . FOR  EXAMPLE:   the monkeys in Harlow’s study showed great distress when they were removed from their biological mothers. In addition, after the study, when the monkeys were placed in situation with other rhesus monkeys (who hadn’t been involved in Harlow’s original research), the rhesus monkeys from the study showed great distress in social situations and were unable to communicate with  other monkeys. In addition, when the monkeys from the study had their own children many were said to neglect their offspring and (in some extreme circumstances) killed their offspring.  EVALUATION:  This is a weakness because  Harlow’s study can be seen to be in breach of the BPS guidelines (it fails to protect the monkeys from harm).  Furthermore,  this study doesn’t tell us anything about the formation of human attachments (monkeys and humans are physiologically different). Therefore Psychologists would argue that the lack of generalizability from this research makes Harlow’s study even more unethical.

Classics in the History of Psychology

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The Nature of Love

Harry F. Harlow (1958) [ 1 ] University of Wisconsin

First published in American Psychologist , 13 , 673-685

Posted March 2000

Address of the President at the sixty-sixth Annual Convention of the American Psychological Association, Washington, D. C., August 31, 1958. First published in American Psychologist , 13 , 573-685.

Love is a wondrous state, deep, tender, and rewarding. Because of its intimate and personal nature it is regarded by some as an improper topic for experimental research. But, whatever our personal feelings may be, our assigned mission as psychologists is to analyze all facets of human and animal behavior into their component variables. So far as love or affection is concerned, psychologists have failed in this mission. The little we know about love does not transcend simple observation, and the little we write about it has been written better by poets and novelists. But of greater concern is the fact that psychologists tend to give progressively less attention to a motive which pervades our entire lives. Psychologists, at least psychologists who write textbooks, not only show no interest in the origin and development of love or affection, but they seem to be unaware of its very existence.

The apparent repression of love by modem psychologists stands in sharp contrast with the attitude taken by many famous and normal people. The word "love" has the highest reference frequency of any word cited in Bartlett's book of Familiar Quotations. It would appear that this emotion has long had a vast interest and fascination for human beings, regardless of the attitude taken by psychologists; but the quotations cited, even by famous and normal people, have a mundane redundancy. These authors and authorities have stolen love from the child and infant and made it the exclusive property of the adolescent and adult.

Thoughtful men, and probably all women, have speculated on the nature of love. From the developmental point of view, the general plan is quite clear: The initial love responses of the human being are those made by the infant to the mother or some mother surrogate. From this intimate attachment of the child to the mother, multiple learned and generalized affectional responses are formed.

Unfortunately, beyond these simple facts we know little about the fundamental variables underlying the formation of affectional responses and little about the mechanisms through which the love of the infant for the mother develops into the multifaceted response patterns characterizing love or affection in the adult. Because of the dearth of experimentation, theories about the fundamental nature of affection have evolved at the level of observation, intuition, and discerning guesswork, whether these have been proposed by psychologists, sociologists, anthropologists, physicians, or psychoanalysts.

The position commonly held by psychologists and sociologists is quite clear: The basic motives are, for the most part, the primary drives -- particularly hunger, thirst, elimination, pain, and sex -- and all other motives, including love or affection, are derived or secondary drives. The mother is associated with the reduction of the primary drives -- particularly hunger, thirst, and pain -- and through learning, affection or love is derived.

It is entirely reasonable to believe that the mother through association with food may become a secondary-reinforcing agent, but this is an inadequate mechanism to account for the persistence of the infant-maternal ties. There is a spate of researches on the formation of secondary reinforcers to hunger and thirst reduction. There can be no question that almost any external stimulus can become a secondary reinforcer if properly associated with tissue-need reduction, but the fact remains that this redundant literature demonstrates unequivocally that such derived drives suffer relatively rapid experimental extinction. Contrariwise, human affection does not extinguish when the mother ceases to have intimate association with the drives in question. Instead, the affectional ties to the mother show a lifelong, unrelenting persistence and, even more surprising, widely expanding generality.

Oddly enough, one of the few psychologists who took a position counter to modern psychological dogma was John B. Watson, who believed that love was an innate emotion elicited by cutaneous stimulation of the erogenous zones. But experimental psychologists, with their peculiar propensity to discover facts that are not true, brushed this theory aside by demonstrating that the human neonate had no differentiable emotions, and they established a fundamental psychological law that prophets are without honor in their own profession.

The psychoanalysts have concerned themselves with the problem of the nature of the development of love in the neonate and infant, using ill and aging human beings as subjects. They have discovered the overwhelming importance of the breast and related this to the oral erotic tendencies developed at an age preceding their subjects' memories. Their theories range from a belief that the infant has an innate need to achieve and suckle at the breast to beliefs not unlike commonly accepted psychological theories. There are exceptions, as seen in the recent writings of John Bowlby, who attributes importance not only to food and thirst satisfaction, but also to "primary object-clinging," a need for intimate physical contact, which is initially associated with the mother.

As far as I know, there exists no direct experimental analysis of the relative importance of the stimulus variables determining the affectional or love responses in the neonatal and infant primate. Unfortunately, the human neonate is a limited experimental subject for such researches because of his inadequate motor capabilities. By the time the human infant's motor responses can be precisely measured, the antecedent determining conditions cannot be defined, having been lost in a jumble and jungle of confounded variables.

Many of these difficulties can be resolved by the use of the neonatal and infant macaque monkey as the subject for the analysis of basic affectional variables. It is possible to make precise measurements in this primate beginning at two to ten days of age, depending upon the maturational status of the individual animal at birth. The macaque infant differs from the human infant in that the monkey is more mature at birth and grows more rapidly; but the basic responses relating to affection, including nursing, contact, clinging, and even visual and auditory exploration, exhibit no fundamental differences in the two species. Even the development of perception, fear, frustration, and learning capability follows very similar sequences in rhesus monkeys and human children.

Three years' experimentation before we started our studies on affection gave us experience with the neonatal monkey. We had separated more than 60 of these animals from their mothers 6 to 12 hours after birth and suckled them on tiny bottles. The infant mortality was only a small fraction of what would have obtained had we let the monkey mothers raise their infants. Our bottle-fed babies were healthier and heavier than monkey-mother-reared infants. We know that we are better monkey mothers than are real monkey mothers thanks to synthetic diets, vitamins, iron extracts, penicillin, chloromycetin, 5% glucose, and constant, tender, loving care.

During the course of these studies we noticed that the laboratory raised babies showed strong attachment to the cloth pads (folded gauze diapers) which were used to cover the hardware-cloth floors of their cages. The infants clung to these pads and engaged in violet temper tantrums when the pads were removed and replaced for sanitary reasons. Such contact-need or responsiveness had been reported previously by Gertrude van Wagenen for the monkey and by Thomas McCulloch and George Haslerud for the chimpanzee and is reminiscent of the devotion often exhibited by human infants to their pillows, blankets, and soft, cuddly stuffed toys. Responsiveness by the one-day-old infant monkey to the cloth pad is shown in Figure 1, and an unusual and strong attachment of a six-month-old infant to the cloth pad is illustrated in Figure 2. The baby, human or monkey, if it is to survive, must clutch at more than a straw.

At this point we decided to study the development of affectional responses of neonatal and infant monkeys to an artificial, inanimate mother, and so we built a surrogate mother which we hoped and believed would be a good surrogate mother. In devising this surrogate mother we were dependent neither upon the capriciousness of evolutionary processes nor upon mutations produced by chance radioactive fallout. Instead, we designed the mother surrogate in terms of modem human engineering principles (Figure 3). We produced a perfectly proportioned, streamlined body stripped of unnecessary bulges and appendices. Redundancy in the surrogate mother's system was avoided by reducing the number of breasts from two to one and placing this unibreast in an upper-thoracic, sagittal position, thus maximizing the natural and known perceptual-motor capabilities of the infant operator. The surrogate was made from a block of wood, covered with sponge rubber, and sheathed in tan cotton terry cloth. A light bulb behind her radiated heat. The result was a mother, soft, warm, and tender, a mother with infinite patience, a mother available twenty-four hours a day, a mother that never scolded her infant and never struck or bit her baby in anger. Furthermore, we designed a mother-machine with maximal maintenance efficiency since failure of any system or function could be resolved by the simple substitution of black boxes and new component parts. It is our opinion that we engineered a very superior monkey mother, although this position is not held universally by the monkey fathers.

One control group of neonatal monkeys was raised on a single wire mother, and a second control group was raised on a single cloth mother. There were no differences between these two groups in amount of milk ingested or in weight gain. The only difference between the two groups lay in the composition of the feces, the softer stools of the wire-mother infants suggesting psychosomatic involvement. The wire mother is biologically adequate but psychologically inept.

We were not surprised to discover that contact comfort was an important basic affectional or love variable, but we did not expect it to overshadow so completely the variable of nursing; indeed; indeed, the disparity is so great as to suggest that the primary function of nursing as an affectional variable is that of insuring frequent and intimate body contact of the infant with the mother. Certainly, man cannot live by milk alone. Love is an emotion that does not need to be bottle- or spoon-fed, and we may be sure that there is nothing to be gained by giving lip service to love.

A charming lady once heard me describe these experiments and, when I subsequently talked to her, her face brightened with sudden insight: "Now I know what's wrong with me," she said, "I'm just a wire mother." Perhaps she was lucky. She might have been a wire wife.

We believe that contact comfort has long served the animal kingdom as a motivating agent for affectional responses. Since at the present time we have no experimental data to substantiate this position, we supply information which must be accepted, if at all, on the basis of face validity:

One function of the real mother, human or subhuman, and presumably of a mother surrogate, is to provide a haven of safety for the infant in times of fear and danger. The frightened or ailing child clings to its mother, not its father; and this selective responsiveness in times of distress, disturbance, or danger may be used as a measure of the strength of affectional bonds. We have tested this kind of differential responsiveness by presenting to the infants in their cages, in the presence of the two mothers, various fear-producing stimuli such as the moving toy bear illustrated in Figure 13. A typical response to a fear stimulus is shown in Figure 14, and the data on differential responsiveness are presented in Figure 15. It is apparent that the cloth mother is highly preferred over the wire one, and this differential selectivity is enhanced by age and experience. In this situation, the variable of nursing appears to be of absolutely no importance: the infant consistently seeks the soft mother surrogate regardless of nursing condition.

Similarly, the mother or mother surrogate provides its young with a source of security, and this role or function is seen with special clarity when mother and child are in a strange situation. At the present time we have completed tests for this relationship on four of our eight baby monkeys assigned to the dual mother-surrogate condition by introducing them for three minutes into the strange environment of a room measuring six feet by six feet by six feet (also called the "open-field test") and containing multiple stimuli known to elicit curiosity-manipulatory responses in baby monkeys. The subjects were placed in this situation twice a week for eight weeks with no mother surrogate present during alternate sessions and the cloth mother present during the others. A cloth diaper was always available as one of the stimuli throughout all sessions. After one or two adaptation sessions, the infants always rushed to the mother surrogate when she was present and clutched her, rubbed their bodies against her, and frequently manipulated her body and face. After a few additional sessions, the infants began to use the mother surrogate as a source of security, a base of operations. As is shown in Figures 16 and 17, they would explore and manipulate a stimulus and then return to the mother before adventuring again into the strange new world. The behavior of these infants was quite different when the mother was absent from the room. Frequently they would freeze in a crouched position, as is illustrated in Figures 18 and 19. Emotionality indices such as vocalization, crouching, rocking, and sucking increased sharply, as shown in Figure 20. Total emotionality score was cut in half when the mother was present. In the absence of the mother some of the experimental monkeys would rush to the center of the room where the mother was customarily placed and then run rapidly from object to object, screaming and crying all the while. Continuous, frantic clutching of their bodies was very common, even when not in the crouching position. These monkeys frequently contacted and clutched the cloth diaper, but this action never pacified them. The same behavior occurred in the presence of the wire mother. No difference between the cloth-mother-fed and wire-mother-fed infants was demonstrated under either condition. Four control infants never raised with a mother surrogate showed the same emotionality scores when the mother was absent as the experimental infants showed in the absence of the mother, but the controls' scores were slightly larger in the presence of the mother surrogate than in her absence.

The first four infant monkeys in the dual mother-surrogate group were separated from their mothers between 165 and 170 days of age and tested for retention during the following 9 days and then at 30-day intervals for six successive months. Affectional retention as measured by the modified Butler box is given in Figure 23. In keeping with the data obtained on adult monkeys by Butler, we find a high rate of responding to any stimulus, even the empty box. But throughout the entire 185-day retention period there is a consistent and significant difference in response frequency to the cloth mother contrasted with either the wire mother or the empty box, and no consistent difference between wire mother and empty box.

Affectional retention was also tested in the open field during the first 9 days after separation and then at 30-day intervals, and each test condition was run twice at each retention interval. The infant's behavior differed from that observed during the period preceding separation. When the cloth mother was present in the post-separation period, the babies rushed to her, climbed up, clung tightly to her, and rubbed their heads and faces against her body. After this initial embrace and reunion, they played on the mother, including biting and tearing at her cloth cover; but they rarely made any attempt to leave her during the test period, nor did they manipulate or play with the objects in the room, in contrast with their behavior before maternal separation. The only exception was the occasional monkey that left the mother surrogate momentarily, grasped the folded piece of paper (one of the standard stimuli in the field), and brought it quickly back to the mother. It appeared that deprivation had enhanced the tie to the mother and rendered the contact-comfort need so prepotent that need for the mother overwhelmed the exploratory motives during the brief, three-minute test sessions. No change in these behaviors was observed throughout the 185-day period. When the mother was absent from the open field, the behavior of the infants was similar in the initial retention test to that during the preseparation tests; but they tended to show gradual adaptation to the open-field situation with repeated testing and, consequently, a reduction in their emotionality scores.

In the last five retention test periods, an additional test was introduced in which the surrogate mother was placed in the center of the room and covered with a clear Plexiglas box. The monkeys were initially disturbed and frustrated when their explorations and manipulations of the box failed to provide contact with the mother. However, all animals adapted to the situation rather rapidly. Soon they used the box as a place of orientation for exploratory and play behavior, made frequent contacts with the objects in the field, and very often brought these objects to the Plexiglas box. The emotionality index was slightly higher than in the condition of the available cloth mothers, but it in no way approached the emotionality level displayed when the cloth mother was absent. Obviously, the infant monkeys gained emotional security by the presence of the mother even though contact was denied.

Affectional retention has also been measured by tests in which the monkey must unfasten a three-device mechanical puzzle to obtain entrance into a compartment containing the mother surrogate. All the trials are initiated by allowing the infant to go through an unlocked door, and in half the trials it finds the mother present and in half, an empty compartment. The door is then locked and a ten-minute test conducted. In tests given prior to separation from the surrogate mothers, some of the infants had solved this puzzle and others had failed. The data of Figure 24 show that on the last test before separation there were no differences in total manipulation under mother-present and mother-absent conditions, but striking differences exist between the two conditions throughout the post-separation test periods. Again, there is no interaction with conditions of feeding.

The over-all picture obtained from surveying the retention data is unequivocal. There is little, if any, waning of responsiveness to the mother throughout this five-month period as indicated by any measure. It becomes perfectly obvious that this affectional bond is highly resistant to forgetting and that it can be retained for very long periods of time by relatively infrequent contact reinforcement. During the next year, retention tests will be conducted at 90-day intervals, and further plans are dependent upon the results obtained. It would appear that affectional responses may show as much resistance to extinction as has been previously demonstrated for learned fears and learned pain, and such data would be in keeping with those of common human observation.

The infant's responses to the mother surrogate in the fear tests, the open-field situation, and the baby Butler box and the responses on the retention tests cannot be described adequately with words. For supplementary information we turn to the motion picture record. (At this point a 20-minute film was presented illustrating and supplementing the behaviors described thus far in the address.)

We have already described the group of four control infants that had never lived in the presence of any mother surrogate and had demonstrated no sign of affection or security in the presence of the cloth mothers introduced in test sessions. When these infants reached the age of 250 days, cubicles containing both a cloth mother and a wire mother were attached to their cages. There was no lactation in these mothers, for the monkeys were on a solid-food diet. The initial reaction of the monkeys to the alterations was one of extreme disturbance. All the infants screamed violently and made repeated attempts to escape the cage whenever the door was opened. They kept a maximum distance from the mother surrogates and exhibited a considerable amount of rocking and crouching behavior, indicative of emotionality. Our first thought was that the critical period for the development of maternally directed affection had passed and that these macaque children were doomed to live as affectional orphans. Fortunately, these behaviors continued for only 12 to 48 hours and then gradually ebbed, changing from indifference to active contact on, and exploration of, the surrogates. The home-cage behavior of these control monkeys slowly became similar to that of the animals raised with the mother surrogates from birth. Their manipulation and play on the cloth mother became progressively more vigorous to the point of actual mutilation, particularly during the morning after the cloth mother had been given her daily change of terry covering. The control subjects were now actively running to the cloth mother when frightened and had to be coaxed from her to be taken from the cage for formal testing.

Objective evidence of these changing behaviors is given in Figure 25, which plots the amount of time these infants spent on the mother surrogates. Within 10 days mean contact time is approximately nine hours, and this measure remains relatively constant throughout the next 30 days. Consistent with the results on the subjects reared from birth with dual mothers, these late-adopted infants spent less than one and one-half hours per day in contact with the wire mothers, and this activity level was relatively constant throughout the test sessions. Although the maximum time that the control monkeys spent on the cloth mother was only about half that Spent by the original dual mother-surrogate group, we cannot be sure that this discrepancy is a function of differential early experience. The control monkeys were about three months older when the mothers were attached to their cages than the experimental animals had been when their mothers were removed and the retention tests begun. Thus, we do not know what the amount of contact would be for a 250-day-old animal raised from birth with surrogate mothers. Nevertheless, the magnitude of the differences and the fact that the contact-time curves for the mothered-from-birth infants had remained constant for almost 150 days suggest that early experience with the mother is a variable of measurable importance.

The control group has also been tested for differential visual exploration after the introduction of the cloth and wire mothers; these behaviors are plotted in Figure 26. By the second test session a high level of exploratory behavior had developed, and the responsiveness to the wire mother and the empty box is significantly greater than that to the cloth mother. This is probably not an artifact since there is every reason to believe that the face of the cloth mother is a fear stimulus to most monkeys that have not had extensive experience with this object during the first 40 to 60 days of life. Within the third test session a sharp change in trend occurs, and the cloth mother is then more frequently viewed than the wire mother or the blank box; this trend continues during the fourth session, producing a significant preference for the cloth mother.

Before the introduction of the mother surrogate into the home-cage situation, only one of the four control monkeys had ever contacted the cloth mother in the open-field tests. In general, the surrogate mother not only gave the infants no security, but instead appeared to serve as a fear stimulus. The emotionality scores of these control subjects were slightly higher during the mother-present test sessions than during the mother-absent test sessions. These behaviors were changed radically by the fourth post-introduction test approximately 60 days later. In the absence of the cloth mothers the emotionality index in this fourth test remains near the earlier level, but the score is reduced by half when the mother is present, a result strikingly similar to that found for infants raised with the dual mother-surrogates from birth. The control infants now show increasing object exploration and play behavior, and they begin to use the mother as a base of operations, as did the infants raised from birth with the mother surrogates. However, there are still definite differences in the behavior of the two groups. The control infants do not rush directly to the mother and clutch her violently; but instead they go toward, and orient around, her, usually after an initial period during which they frequently show disturbed behavior, exploratory behavior, or both.

That the control monkeys develop affection or love for the cloth mother when she is introduced into the cage at 250 days of age cannot be questioned. There is every reason to believe, however, that this interval of delay depresses the intensity of the affectional response below that of the infant monkeys that were surrogate-mothered from birth onward. In interpreting these data it is well to remember that the control monkeys had had continuous opportunity to observe and hear other monkeys housed in adjacent cages and that they had had limited opportunity to view and contact surrogate mothers in the test situations, even though they did not exploit the opportunities.

During the last two years we have observed the behavior of two infants raised by their own mothers. Love for the real mother and love for the surrogate mother appear to be very similar. The baby macaque spends many hours a day clinging to its real mother. If away from the mother when frightened, it rushes to her and in her presence shows comfort and composure. As far as we can observe, the infant monkey's affection for the real mother is strong, but no stronger than that of the experimental monkey for the surrogate cloth mother, and the security that the infant gains from the presence of the real mother is no greater than the security it gains from a cloth surrogate. Next year we hope to put this problem to final, definitive, experimental test. But, whether the mother is real or a cloth surrogate, there does develop a deep and abiding bond between mother and child. In one case it may be the call of the wild and in the other the McCall of civilization, but in both cases there is "togetherness."

In spite of the importance of contact comfort, there is reason to believe that other variables of measurable importance will be discovered. Postural support may be such a variable, and it has been suggested that, when we build arms into the mother surrogate, 10 is the minimal number required to provide adequate child care. Rocking motion may be such a variable, and we are comparing rocking and stationary mother surrogates and inclined planes. The differential responsiveness to cloth mother and cloth-covered inclined plane suggests that clinging as well as contact is an affectional variable of importance. Sounds, particularly natural, maternal sounds, may operate as either unlearned or learned affectional variables. Visual responsiveness may be such a variable, and it is possible that some semblance of visual imprinting may develop in the neonatal monkey. There are indications that this becomes a variable of importance during the course of infancy through some maturational process.

John Bowlby has suggested that there is an affectional variable which he calls "primary object following," characterized by visual and oral search of the mother's face. Our surrogate-mother-raised baby monkeys are at first inattentive to her face, as are human neonates to human mother faces. But by 30 days of age ever-increasing responsiveness to the mother's face appears -- whether through learning, maturation, or both -- and we have reason to believe that the face becomes an object of special attention.

Our first surrogate-mother-raised baby had a mother whose head was just a ball of wood since the baby was a month early and we had not had time to design a more esthetic head and face. This baby had contact with the blank-faced mother for 180 days and was then placed with two cloth mothers, one motionless and one rocking, both being endowed with painted, ornamented faces. To our surprise the animal would compulsively rotate both faces 180 degrees so that it viewed only a round, smooth face and never the painted, ornamented face. Furthermore, it would do this as long as the patience of the experimenter in reorienting the faces persisted. The monkey showed no sign of fear or anxiety, but it showed unlimited persistence. Subsequently it improved its technique, compulsively removing the heads and rolling them into its cage as fast as they were returned. We are intrigued by this observation, and we plan to examine systematically the role of the mother face in the development of infant-monkey affections. Indeed, these observations suggest the need for a series of ethological-type researches on the two-faced female.

Although we have made no attempts thus far to study the generalization of infant-macaque affection or love, the techniques which we have developed offer promise in this uncharted field. Beyond this, there are few if any technical difficulties in studying the affection of the actual, living mother for the child, and the techniques developed can be utilized and expanded for the analysis and developmental study of father-infant and infant-infant affection.

Since we can measure neonatal and infant affectional responses to mother surrogates, and since we know they are strong and persisting, we are in a position to assess the effects of feeding and contactual schedules; consistency and inconsistency in the mother surrogates; and early, intermediate, and late maternal deprivation. Again, we have here a family of problems of fundamental interest and theoretical importance.

If the researches completed and proposed make a contribution, I shall be grateful; but I have also given full thought to possible practical applications. The socioeconomic demands of the present and the threatened socioeconomic demands of the future have led the American woman to displace, or threaten to displace, the American man in science and industry. If this process continues, the problem of proper child-rearing practices faces us with startling clarity. It is cheering in view of this trend to realize that the American male is physically endowed with all the really essential equipment to compete with the American female on equal terms in one essential activity: the rearing of infants. We now know that women in the working classes are not needed in the home because of their primary mammalian capabilities; and it is possible that in the foreseeable future neonatal nursing will not be regarded as a necessity, but as a luxury ---to use Veblen's term -- a form of conspicuous consumption limited perhaps to the upper classes. But whatever course history may take, it is comforting to know that we are now in contact with the nature of love.

[1] The researches reported in this paper were supported by funds supplied by Grant No. M-722, National Institutes of Health, by a grant from the Ford Foundation, and by funds received from the Graduate School of the University of Wisconsin.

Harlow’s Monkey Experiment (Definition + Contribution to Psychology)

Not all experiments in psychology involve humans; nevertheless, those utilizing animals often aim to shed light on human behavior. Harlow's Monkey experiments had a significant impact on psychology, and despite being considered controversial, they remain influential to this day.

What Are Harlow’s Monkey Experiments?

Harlow's Monkey experiments looked at the influence of parental guidance and interaction during early development. Infant monkeys were placed in isolation, away from their mothers. In other experiments, he took infant monkeys away from their mothers but placed them in a cage with “surrogate” mothers.

In both sets of experiments, he found that the monkeys displayed a specific set of behaviors as a response to their unusual upbringing.

Psychology Before Harlow's Monkey Experiments

Harry Harlow, the man behind the monkey experiments, was a psychologist in the first half of the 20th century. At the time, some conflicting ideas were going around about parenting styles.

Early behaviorists didn’t think parents should be so cuddly. Watson told parents that lots of physical affection would slow down their development.

For years, psychology students were taught that B.F. Skinner’s daughter was subject to the behaviorist’s experiments, and she went crazy after being isolated in a glass box for the first year of her life. Skinner said that she was raised just fine in isolation. (Skinner’s daughter refutes some rumors in a Guardian article .)

As time went on, psychoanalysts like Freud theorized that a child’s development was stunted if the mother didn’t provide love and attention in the first year of the child’s life. If a child experienced trauma during this year, they would develop an oral fixation. After all, getting fed was the most important experience in the first year of a child’s life.

There were a lot of different ideas on how to raise a child. And it makes sense that most parents wanted to do the “right” thing.

So psychologists started to build experiments to test some of these theories. Harry Harlow was one of them. But rather than studying children, he studied rhesus monkeys. His experiments were very different from a lot of psychologists at the time. He wanted to focus on the impact of love and basic physiological needs.

What Happened During Harlow's Monkey Experiments?

The monkeys in isolation were separated from other monkeys for 3-12 months. During that time, some would display behaviors to possibly “self-soothe.” Others would self-mutilate. They would circle anxiously and appear to be distressed.

Harlow also studied what happened when these monkeys were placed back in the company of other monkeys. The results were slightly disturbing. They continued to self-mutilate. They couldn’t integrate themselves into society. These isolated monkeys were scared, aggressive, or dumbfounded. Some of the monkeys died after they stopped eating.

Harlow noted that the longer the monkeys stayed in isolation, the harder it was for them to integrate into society.

Monkeys With Wire or Cloth Mothers

So the monkeys were negatively affected by isolation. But Harlow wanted to go further. Why were the monkeys impacted so significantly? Was it solely because of physiological factors, or did love and affection play a role?

To answer these questions, Harlow set up another experiment. He took the infant monkeys away from their mothers and placed them in a cage with two “surrogate” mothers. One of these surrogate mothers was made out of wire. The other was made out of cloth.

In some cages, the wire mother had food for the monkeys. The cloth mother did not. In other cases, the cloth mother had food for the monkeys. The wire mother did not.

Harlow observed that no matter which surrogate mother held the food, the infants would spend more time with the comforting cloth mother. If only the wire mother had food, the monkeys would only go to them when hungry. Otherwise, they would stay in the comfort of the cloth mother.

This doesn’t mean that the monkeys were fully developed socially. When these monkeys were placed back into cages with other monkeys, they didn’t integrate well. They were shy, didn’t stand up for themselves if bullied, and had trouble mating. The monkeys that did become mothers also had trouble raising their monkeys. Harlow believed these behaviors resulted from the events in their infancy.

Attachment Theory and Harlow's Monkey Experiments

Suppose you have ever read anything from relationship experts or counselors. In that case, you might hear this idea: our relationship with our parents influences the partners we pick and the way we go about relationships. Many psychologists have shared variations of this idea. Some of these variations are cringe-worthy, and some are quite helpful.

One variation of this idea is Attachment Theory . This theory describes four different types of attachments that we develop based on our relationship with our parents. We bring this attachment style (secure, anxious, etc.) into adult relationships.

Attachment Theory was the product of studies conducted by John Bowlby and Mary Ainsworth. However, their studies are not the only ones influencing how we view attachment formation. One set of experiments, Harlow’s Monkey experiments, played a role in influencing how we view attachment. Due to the unethical nature of this experiment, it’s not always discussed in a psychology class or discussions about relationships.

Controversy and Other Studies on Attachment

If you think, “Those poor monkeys!” you’re not alone. Many people believed that Harlow’s experiments were unethical. Why would you subject live animals to an experiment that would ultimately traumatize them? Remember, some of these monkeys died early due to starvation caused by anxious behaviors. Did those monkeys need to die for the good of science?

While some say yes, others say no. Not all studies on attachment took such harsh measures. For example, John Bowlby and Mary Ainsworth observed parents and children as parents left the room for a few minutes at a time. You can learn more about these studies, and the Attachment Styles developed as a result of these studies in another video.

Despite the controversy surrounding his experiments, Harlow did positively impact the world of psychology and parenting. The risks he took for studying love and care, when those topics weren’t discussed in psychology, paid off. His work showed the importance of love and affection. Caregivers, parents, and guardians took note. If your parents or grandparents showed you love and affection as a child, you can thank the research of Harry Harlow and other psychologists who studied Attachment and development.

Related posts:

• Dreams Of Monkeys Meaning (12 Reasons + Interpretation)
• Attachment Styles Theory (Free Test)
• John Bowlby Biography - Contributions To Psychology
• Mary Ainsworth (Biography)
• Golden Child Syndrome (Definition + Examples)

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Harry Harlow and the Nature of Affection

What Harlow's Infamous Monkey Mother Experiments Revealed

• Love and Affection
• Harry Harlow's Research on Love
• Wire Mother Experiment
• Fear and Security

Impact of Harry Harlow’s Research

Frequently asked questions.

Harry Harlow was one of the first psychologists to scientifically investigate the nature of human love and affection. Through a series of controversial monkey mother experiments, Harlow was able to demonstrate the importance of early attachments, affection, and emotional bonds in the course of healthy development.

This article discusses his famous monkey mother experiments and what the results revealed. It also explores why Harlow's monkey experiments are so unethical and controversial.

Early Research On Love

During the first half of the 20th century, many psychologists believed that showing affection towards children was merely a sentimental gesture that served no real purpose. According to many thinkers of the day, affection would only spread diseases and lead to adult psychological problems.

"When you are tempted to pet your child, remember that mother love is a dangerous instrument," the behaviorist John B. Watson once even went so far as to warn parents.

Psychologists were motivated to prove their field as a rigorous science. The behaviorist movement dominated the field of psychology during this time. This approach urged researchers to study only observable and measurable behaviors.

An American psychologist named Harry Harlow , however, became interested in studying a topic that was not so easy to quantify and measure—love. In a series of controversial experiments conducted during the 1960s, Harlow demonstrated the powerful effects of love and in particular, the absence of love.   

His work demonstrated the devastating effects of deprivation on young rhesus monkeys. Harlow's research revealed the importance of a caregiver's love for healthy childhood development.

Harlow's experiments were often unethical and shockingly cruel , yet they uncovered fundamental truths that have influenced our understanding of child development.

Harry Harlow's Research on Love

Harlow noted that very little attention had been devoted to the experimental research of love. At the time, most observations were largely philosophical and anecdotal.

"Because of the dearth of experimentation, theories about the fundamental nature of affection have evolved at the level of observation, intuition, and discerning guesswork, whether these have been proposed by psychologists, sociologists, anthropologists, physicians, or psychoanalysts ," he noted.

Many of the existing theories of love centered on the idea that the earliest attachment between a mother and child was merely a means for the child to obtain food, relieve thirst, and avoid pain. Harlow, however, believed that this behavioral view of mother-child attachments was an inadequate explanation.

The Monkey Mother Experiment

His most famous experiment involved giving young rhesus monkeys a choice between two different "mothers." One was made of soft terrycloth but provided no food. The other was made of wire but provided nourishment from an attached baby bottle.

Harlow removed young monkeys from their natural mothers a few hours after birth and left them to be "raised" by these mother surrogates. The experiment demonstrated that the baby monkeys spent significantly more time with their cloth mother than with their wire mother.

In other words, the infant monkeys went to the wire mother only for food but preferred to spend their time with the soft, comforting cloth mother when they were not eating.

Based on these findings, Harry Harlow concluded that affection was the primary force behind the need for closeness.

Harry Harlow's Further Research

Later research demonstrated that young monkeys would also turn to their cloth surrogate mother for comfort and security. Such work revealed that affectionate bonds were critical for development.

Harlow utilized a "strange situation" technique similar to the one created by attachment researcher Mary Ainsworth . Young monkeys were allowed to explore a room either in the presence of their surrogate mother or in her absence.

Monkeys who were with their cloth mother would use her as a secure base to explore the room. When the surrogate mothers were removed from the room, the effects were dramatic. The young monkeys no longer had their secure base for exploration and would often freeze up, crouch, rock, scream, and cry.

Harry Harlow’s experiments offered irrefutable proof that love is vital for normal childhood development . Additional experiments by Harlow revealed the long-term devastation caused by deprivation, leading to profound psychological and emotional distress and even death.

Harlow’s work, as well as important research by psychologists John Bowlby and Mary Ainsworth, helped influence key changes in how orphanages, adoption agencies, social services groups, and childcare providers approached the care of children.

Harlow's work led to acclaim and generated a wealth of research on love, affection, and interpersonal relationships. However, his own personal life was marked by conflict.

After the terminal illness of his wife, he became engulfed by alcohol misuse and depression, eventually becoming estranged from his own children. Colleagues frequently described him as sarcastic, mean-spirited, misanthropic, chauvinistic, and cruel.

While he was treated for depression and eventually returned to work, his interests shifted following the death of his wife. He no longer focused on maternal attachment and instead developed an interest in depression and isolation.

Despite the turmoil that marked his later personal life, Harlow's enduring legacy reinforced the importance of emotional support, affection, and love in the development of children.

A Word From Verywell

Harry Harlow's work was controversial in his own time and continues to draw criticism today. While such experiments present major ethical dilemmas, his work helped inspire a shift in the way that we think about children and development and helped researchers better understand both the nature and importance of love.

Harlow's research demonstrated the importance of love and affection, specifically contact comfort, for healthy childhood development. His research demonstrated that children become attached to caregivers that provide warmth and love, and that this love is not simply based on providing nourishment. 

Harlow's monkey mother experiment was unethical because of the treatment of the infant monkeys. The original monkey mother experiments were unnecessarily cruel. The infant monkeys were deprived of maternal care and social contact.

In later experiments, Harlow kept monkeys in total isolation in what he himself dubbed a "pit of despair." While the experiments provided insight into the importance of comfort contact for early childhood development, the research was cruel and unethical.

Hu TY, Li J, Jia H, Xie X. Helping others, warming yourself: altruistic behaviors increase warmth feelings of the ambient environment . Front Psychol . 2016;7:1349. doi:10.3389/fpsyg.2016.01349

Suomi SJ. Risk, resilience, and gene-environment interplay in primates . J Can Acad Child Adolesc Psychiatry . 2011;20(4):289-297.

Zhang B. Consequences of early adverse rearing experience(EARE) on development: insights from non-human primate studies . Zool Res . 2017;38(1):7-35. doi:10.13918/j.issn.2095-8137.2017.002

Harlow HF. The nature of love .  American Psychologist. 1958;13(12):673-685. doi:10.1037/h0047884

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Ottaviani J, Meconis D. Wire Mothers: Harry Harlow and the Science of Love . Ann Arbor, MI: G.T. Labs; 2007.

By Kendra Cherry, MSEd Kendra Cherry, MS, is a psychosocial rehabilitation specialist, psychology educator, and author of the "Everything Psychology Book."

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Unveiling Human Attachment: Insights from Harlow’s Monkey Experiments

By declan fitzpatrick, this article is divided into the following sections:.

The Harlow Monkey Experiments, conducted in the 1950s and 1960s by psychologist Harry Harlow, revolutionized our understanding of attachment and developmental psychology. Through a series of groundbreaking studies involving rhesus monkeys, Harlow challenged prevailing notions about the nature of love and the importance of maternal bonding.

By examining the methodology, findings, and implications of the Harlow Monkey Experiments, we can gain profound insights into the essential role of emotional and social connections in early development.

Methodology and Design

Harry Harlow’s experiments aimed to investigate the significance of caregiving and companionship in the cognitive and social growth of primates. He constructed surrogate mothers using wire and cloth, allowing him to isolate and analyze the factors contributing to attachment. Infant rhesus monkeys were separated from their biological mothers shortly after birth and placed in cages with two surrogate mothers—one made of wire that provided food and one covered in soft cloth that offered no nourishment. This setup enabled Harlow to observe the monkeys’ preferences and behaviors in choosing between comfort and sustenance.

Through meticulously designed experiments, Harlow observed how the infant monkeys interacted with the surrogates. He introduced various stressors to assess the monkeys’ responses and their reliance on the surrogate mothers for comfort and security. These controlled conditions allowed for a detailed examination of the emotional bonds formed between the infants and their surrogate caregivers.

Key Findings

The findings of the Harlow Monkey Experiments were both surprising and enlightening. Contrary to the dominant belief that attachment was primarily driven by the provision of food, Harlow discovered that the infant monkeys overwhelmingly preferred the cloth surrogate over the wire one, even when the latter provided nourishment. This preference for tactile comfort highlighted the critical role of contact comfort in the formation of attachment bonds.

Harlow’s experiments demonstrated that the need for affection and emotional security outweighed the basic need for food. The monkeys turned to the cloth surrogate when frightened or stressed, seeking solace and reassurance. These behaviors underscored the importance of a nurturing and comforting presence in fostering healthy psychological development.

Emotional and Social Implications

The implications of the Harlow Monkey Experiments extended beyond the realm of animal behavior, offering profound insights into human development as well. Harlow’s research challenged the then-prevalent behaviorist view that attachment was solely based on conditioned responses related to feeding. Instead, his findings emphasized the intrinsic need for warmth, comfort, and emotional connection in the development of secure and healthy attachments.

The experiments revealed that deprivation of meaningful social and emotional interaction had detrimental effects on the monkeys’ overall well-being. Monkeys raised with only the wire surrogate exhibited signs of severe emotional distress, social withdrawal, and abnormal behaviors. These findings drew attention to the potential consequences of neglect and lack of emotional support in human children, emphasizing the necessity of nurturing environments for optimal development.

Ethical Considerations

Despite its groundbreaking contributions, the Harlow Monkey Experiments have been scrutinized for their ethical implications. The experiments involved significant psychological and emotional distress for the infant monkeys, raising concerns about the moral treatment of animals in research. The isolation and deprivation experienced by the monkeys led to long-term negative outcomes, prompting debates about the ethical boundaries of experimental psychology.

In response to these concerns, the field of psychology has since established stricter ethical guidelines to ensure the humane treatment of animals in research. These guidelines emphasize the importance of minimizing harm and distress, promoting welfare, and considering alternative methods whenever possible. Harlow’s work, while controversial, played a role in shaping the ethical standards that govern contemporary psychological research.

Broader Societal Impact

The Harlow Monkey Experiments had a significant impact on various fields, including psychology, pediatrics, and child development. The insights gained from these studies prompted a reevaluation of childcare practices, highlighting the vital importance of emotional bonding and physical affection in early childhood. Harlow’s research influenced policies and practices related to parenting, adoption, and early childhood education, emphasizing the need for responsive and nurturing caregiving.

The findings also resonated within the context of hospital care for infants and children. Prior to Harlow’s work, institutionalized children often received minimal physical affection, leading to adverse developmental outcomes. The Harlow Monkey Experiments underscored the necessity of providing emotional and social support, shaping guidelines for more humane and effective caregiving practices.

Theoretical Contributions

Harlow’s research contributed to the theoretical framework of attachment theory, which was further developed by psychologists such as John Bowlby and Mary Ainsworth . Attachment theory posits that early relationships with caregivers form the foundation for future social and emotional development. Harlow’s empirical evidence supported Bowlby’s concept of the “secure base,” where a nurturing caregiver provides a sense of safety and security, allowing the child to explore and engage with the world confidently.

The Harlow Monkey Experiments illustrated the profound impact of early attachment experiences on later behavior, validating the notion that secure attachments foster resilience and healthy psychological functioning. These findings continue to inform therapeutic approaches, particularly in addressing attachment disorders and trauma in children and adolescents.

The Harlow Monkey Experiments represent a landmark in the study of attachment and developmental psychology. Through his innovative and, at times, controversial research, Harry Harlow unveiled the fundamental importance of emotional and social bonds in early development. The experiments challenged conventional wisdom, demonstrating that the need for comfort and security profoundly shapes attachment behaviors.

While the ethical considerations surrounding the Harlow Monkey Experiments highlight the complex balance between scientific discovery and moral responsibility, the insights gained have had lasting implications. Harlow’s work has influenced childcare practices, theoretical frameworks, and therapeutic interventions, underscoring the critical role of nurturing and affectionate caregiving in fostering healthy development.

As we reflect on the legacy of the Harlow Monkey Experiments, it is clear our quest for understanding human attachment continues to evolve. By building on Harlow’s research and adhering to ethical standards, we can further our knowledge of the intricate interplay between emotional connections and psychological well-being, ultimately enhancing the lives of individuals and communities.

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“When Strangers Meet”: John Bowlby and Harry Harlow on Attachment Behavior

• Glimpse from the Past
• Open access
• Published: 03 September 2008
• Volume 42 , pages 370–388, ( 2008 )

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• Frank C. P. van der Horst 1 ,
• Helen A. LeRoy 2 &
• René van der Veer 1  

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From 1957 through the mid-1970s, John Bowlby, one of the founders of attachment theory, was in close personal and scientific contact with Harry Harlow. In constructing his new theory on the nature of the bond between children and their caregivers, Bowlby profited highly from Harlow’s experimental work with rhesus monkeys. Harlow in his turn was influenced and inspired by Bowlby’s new thinking. On the basis of the correspondence between Harlow and Bowlby, their mutual participation in scientific meetings, archival materials, and an analysis of their scholarly writings, both the personal relationship between John Bowlby and Harry Harlow and the cross-fertilization of their work are described.

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Introduction

Today, one can pick up almost any introductory, general, or developmental psychology textbook (e.g., DeHart et al. 2004 ; Cole and Cole 2005 ) and find references to British child psychiatrist John Bowlby (1907–1990) and American animal psychologist Harry Harlow (1905–1981). Quite often their work is discussed in tandem. Bowlby was a clinician by training and Harlow an experimentalist. Despite these rather different backgrounds, the two men had several things in common. One of them was that they showed no hesitation in expressing views that went against the prevailing Zeitgeist . In the 1950s and 1960s, both Bowlby and Harlow formulated new ideas on the nature of the bond between child and caregiver. They defied the prevailing psychoanalytic and learning theoretical views that dominated psychological thinking from the 1930s. Although it has been argued (Singer 1975 ) that Harlow’s experimenting had no influence on Bowlby’s theorizing, here it will become clear that Bowlby used Harlow’s surrogate work with rhesus monkeys as much needed empirical support for his emerging theory of attachment in which he explained the nature and function of the affectional bonds between children and their caregivers (Bowlby 1958 , 1969/ 1982 ). In his turn, Harlow was influenced by Bowlby’s thinking and tried to model his rhesus work to support Bowlby’s new theoretical framework (e.g., Seay et al. 1962 ; Seay and Harlow 1965 ).

The theories of Harlow and Bowlby are well-known but so far little was known about the personal and professional relationships between these two giants in the field. In this contribution, on the basis of the correspondence between Harlow and Bowlby Footnote 1 , their joint participation in scientific meetings, archival materials, and an analysis of their scholarly writings, an attempt is made to delineate the cross-fertilization of their work during the most active years of their acquaintance from 1957 through the mid-1970s. It will be demonstrated that Bowlby and Harlow’s interests converged as Harlow shifted his focus to a developmental approach shortly before the two met. Their introduction at a distance by British ethologist Robert Hinde was the beginning of an exchange of ideas that resulted in groundbreaking experimenting and theorizing that affects the field of developmental psychology to this day.

Bowlby’s Early Career (1938–1957): from Kleinian Psychoanalysis to Real Life

John Bowlby, who received a Master’s degree from Cambridge University and an M.D. from University College Hospital in London, was trained in psychoanalysis. He practiced as a clinician and joined the staff of the Tavistock Clinic in London in 1946, where he spent the remainder of his professional career (cf. Van Dijken 1998 ; Van Dijken et al. 1998 ). There is no doubt that he will be remembered in history as “the father of attachment theory”. Bowlby’s career evolved on the basis of a single theme, the relationship between mother and infant, and the effects of the pattern established early on upon the developmental outcome of the offspring. He mounted a scientific challenge to dominant psychoanalytical views in British psychiatry, such as those held by Anna Freud and Melanie Klein (Berrios and Freeman 1991 ).

In an interview with Robert Karen ( 1994 , pp. 45–46), Bowlby described an influential experience in 1938, while training under the supervision of psychoanalyst Melanie Klein. Contrary to Klein, who believed all behavior was motivated by inner feelings, Bowlby felt that external relationships, e.g., the way a parent treated a child, were important to consider in understanding the child’s behavior. At the time, he was seeing an anxious, hyperactive child as a patient five days a week. The boy’s mother would sit in the waiting room, and Bowlby noticed that she too seemed quite anxious and unhappy. When he told Klein he wanted to talk to the mother as well, Klein refused adamantly, dismissing the mother as a possible causal or related factor in the child’s behavior. Bowlby was thoroughly annoyed and gradually distanced himself from the Melanie Klein school of thought. Later, in 1948, through the work of Tavistock social worker James Robertson, with whom he would work closely over the years, Bowlby became interested in recording the responses shown by children between the ages of 12 months and 4 years upon separation from their mothers or attachment figures (Bowlby 1960a ).

In 1950, as part of a World Health Organization (WHO) project, Bowlby ( 1951 ) undertook a literature survey in order to test the hypothesis that “separation experiences are pathogenic” (Bowlby 1958 ). Homeless children had become a major problem after World War II, and in his WHO report, Bowlby warned that children deprived of their mothers were at risk for physical and mental illness. After surveying the literature, Bowlby et al. ( 1952 , p. 82) concluded:

It became clear that this hypothesis is well supported by evidence and the team is now planning to concentrate on understanding the psychological processes which lead to the grave personality disturbances—severe anxiety conditions and psychopathic personality—which we now know sometimes follow experiences of separation.

We may conclude, then, that Bowlby was convinced at the time that (repeated) separation experiences may seriously harm the mental health of children and that the existing literature (e.g. on hospitalization) proved his point of view. He valued empirical studies and emphasized the importance of objective observation of real-life experiences. However, he still lacked the theoretical apparatus to understand the causal mechanisms behind the phenomena he observed. Also, he knew of no experiments that manipulated the potentially relevant variables in the domain of attachment formation. It was in this situation that he chanced upon the emerging science of ethology and the experimental work of Harlow.

In the subsequent years Bowlby made increasing use of ethological findings and theorizing guided by British ethologist, colleague and life-long friend Robert Hinde (Van der Horst et al. 2007 ). Bowlby ( 1957 , 1960c ) acknowledged a deep and pervasive interest in ethology beginning about 1951, which was sparked by Konrad Lorenz’s ( 1935 , 1937 ) gosling work. His talk to the members of the British Psycho-Analytical Society on June 19, 1957 (published as Bowlby 1958 ) testifies of his growing confidence in the relevance of ethology.

Harlow’s Early Career (1930–1957): from Conditioning Rats to Studying Monkey Love

Harry Harlow received a Ph.D. in psychology from Stanford University in 1930 and spent the remainder of his academic career as a professor at the University of Wisconsin—Madison. Harlow was educated in the psychological tradition of the 1920s and 1930s, a time when psychology was making an effort to become a ‘real’ science. Studying behavior was a case of controlling the environment and varying one particular condition. It was a time when behaviorist views carried the day and the conditioned responses of Norwegian rats were the key to understanding mental life. So, when Harlow was appointed at Wisconsin in 1930 and found that the psychology department’s chairman had the rat laboratory dismantled and it was not about to be replaced, he was greatly inconvenienced (Harlow 1977 , p. 138–139; Suomi and LeRoy 1982 ).

It was only at the suggestion of the chairman’s wife that Harlow decided to study primates at the local zoo and he soon found out that the intellectual capabilities of the monkeys were far greater than those of rats (Suomi and LeRoy 1982 ). To study these capabilities more rigorously and effectively Harlow developed the Wisconsin General Test Apparatus (WGTA; Harlow and Bromer 1938 ) by which it was possible to present the monkeys with a large number of learning tests in a highly standardized way. With it he tested the monkeys with discrimination learning and memory tasks (e.g., Harlow 1943 , 1944 ). Harlow’s next step was to study cortical localization of learning capabilities by doing lesion studies with monkeys (e.g., Harlow and Dagnon 1943 ; Harlow and Settlage 1947 ; Moss and Harlow 1948 ). By lesioning different areas of the brain, Harlow noted that each of the operated monkeys performed differently on the WGTA tests. This work was basically similar to the work done by Lashley (e.g., Lashley 1950 ).

In the late 1940s, Harlow achieved “a major conceptual and methodological breakthrough” (Suomi and LeRoy 1982 , p. 321) by identifying the formation of learning sets in monkeys (Harlow 1949 ). Harlow demonstrated that his monkeys “learned to learn” and that they acquired a strategy for problem-solving. As methods of studying processes underlying monkey learning were exhausted, Harlow in the early 1950s turned to studying motivation and the ontogeny of learning. This type of developmental research required the establishment of a breeding colony of rhesus monkeys. It was at this point that Harlow’s attention was drawn to the phenomenon of affection.

Harlow had always had problems importing monkeys: apart from being very expensive, they were often ill upon arrival and infected the other monkeys in the laboratory. In 1956, following procedures of Van Wagenen ( 1950 ), he decided to raise his own rhesus monkeys, and thus the Wisconsin lab became the first self-sustaining colony of monkeys in the US. The monkeys were kept separated at all times to avoid any spread of disease. The results of this procedure were remarkable for those who could see it: the monkeys Harlow raised were physically perfectly healthy, but their social behavior was very awkward. They were simply unable to socially interact with each other. Another striking observation Harlow made was that the infant monkeys “clung to [the diapers on the floor of their cage] and engaged in violent temper tantrums when the pads were removed and replaced for sanitary reasons” (Harlow 1958 , p. 675). Harlow wondered whether these observations could mean anything for the needs of human children.

Just two months prior to Bowlby’s British Psycho-Analytical Society address which discussed in great depth the child’s tie to the mother, Harlow spoke on April 20, 1957 at a conference in Washington, D.C. The title of his address was the “Experimental Analysis of Behavior” and it included a discussion of trends in this area. Harlow began his address by stating that “no behavior is too complicated to analyze experimentally, if only the proper techniques can be discovered and developed” (Harlow 1957 , p. 485). He went on to emphasize the importance of a developing trend toward longitudinal studies (psychology had traditionally been concerned with a cross-sectional approach), and he told how:

I have followed with interest the changes in my own research programs and the development of these programs. The experimental S that has consumed almost all my research time has been the rhesus monkey. When I initially approached the experimental analysis of this animal’s behavior, I approached it in the classical, cross-sectional manner (...). If it had not been for the fact that my monkey S s continued to live after they had solved a problem and that they were not expendable in view of the available financial support, I might still be engaged in cross-sectional studies of the monkey’s behavior. (Harlow 1957 , p. 487)

These comments clearly indicate that Harlow was moving towards experimental developmental research, the type of research that Bowlby so badly needed at the time. Harlow was now on the threshold of the affectional studies, for which he would become famous. He explained that:

More recently we have planned and initiated much more extensive longitudinal studies in which we have separated infant rhesus monkeys from their mothers at birth and raised them under the controlled conditions of the laboratory. We have been successful in raising over fifty of these young animals, and we have obtained data on their learning development from birth through three years of age. (...) We have found the longitudinal approach to the experimental analysis of behavior interesting and even exciting, and we are now extending this type of analysis to other areas than learning, perception, and motivation. (...) [W]e are planning and conducting systematic longitudinal studies on the development of emotional responses. (Harlow 1957 , p. 488)

Just like Bowlby before his fellow psychiatrists of the British Psycho-Analytical society , Harlow ( 1957 , p. 490), before an audience of clinical psychologists, stressed the importance of observational methods in this process, something that was of course very obvious to him.

At the present time (...) we are interested in tracing the development of various patterns of emotional behavior. (...) We began by looking for response patterns which might fit. (...) But this observational study (...) is gradually taking on the characteristics of an experiment. As we gain sophistication about the monkey’s emotional responses, we become more selective in the patterns which we observe.

It was because of their mutual interest in this area of emotional behavior and responses that Harlow and Bowlby became acquainted. In Harlow’s words: “It is an understatement to add that we have research interests in common” (Harlow in a letter to Bowlby, January 27, 1958).

Ethology and Animal Psychology: Contrasting Approaches to Animal Behavior

It was not self-evident for a British ethologically oriented psychiatrist and an American animal behaviorist to meet in those days. In the 1950s, there was a great barrier between ethologists (who were mostly biologists by training) and students of animal behavior (mostly psychologists). Ethologists emphasized observation of animals in their natural habitat, whereas comparative psychologists relied on rigorous experimentation in the laboratory. The culmination of this debate was a 1953 critique by Theodore Schneirla’s student Daniel Lehrman of Lorenz’s concept of instinct, at that time the central theoretical construct of ethology (Lehrman 1953 ). But in contrast to what might be expected, when Lehrman visited Europe in 1954 and met with leading ethologists, he was very well received. Just like many of the ethologists, Lehrman had a background in evolutionary biology and ornithology and this may have been essential in bridging their differences. Although Lorenz never acknowledged Lehrman’s ideas, they later became mainstream ethology (Griffiths 2004 ). Eventually Hinde ( 1966 ) wrote his authoritative book Animal behaviour which was essentially “a synthesis of ethology and comparative psychology” (cf. Van der Horst et al. 2007 , p. 9–10).

In this climate of contrasting views, Hinde and Harlow met for the first time in Palo Alto in early 1957 at a conference organized by Frank Beach that was intended to bring together a group of European ethologists (Niko Tinbergen, Gerard Baerends, Jan van Iersel, David Vowles, Eckhardt Hess and Robert Hinde) with a group of mainly North-American comparative and experimental psychologists (Frank Beach, Donald Hebb, Daniel Lehrman, Jay Rosenblatt, Karl Lashley and Harry Harlow). Hinde has good memories of the event: “It was a wonderful conference, about three weeks, [where you had] nothing to publish, and if you did not finish what you had to say today there was always tomorrow” (Robert Hinde, personal communication, March 14, 2007). After their first encounter, Hinde and Harlow met several times in the late fifties and sixties. Although they influenced each other and their relationship was very cordial in the days they interacted, Hinde in retrospect remembers that at that time their approaches were still rather far apart:

I must have next met Harry when I visited Madison and was appalled by this room full of cages with babies going “whoowhoowhoo” and Harlow had no sensitivity at that point that he was damaging these infants. At that time I was beginning to work on mother–infant relations in monkeys myself, but I already knew enough about monkeys to know that that “whoo”-call was a distress call. These experiments had their restrictions, but they did show certain important things. After that I saw him at least once a year for a while as he asked me to join his scientific committee. Of course his results influenced my way of thinking, but I was then an ethologist and not keen on his laboratory orientation. And I could never have attempted to do the sort of research that he did because our colony only had six adult males and two or three females in each group. We attempted to create an approximation to a normal social situation: it was a long way off, of course, but at least it was social. (Robert Hinde, personal communication, August 22 and 26, 2005; March 14, 2007)

Despite these differences in theoretical orientation, it was Robert Hinde who would eventually establish contact between Bowlby and Harlow. At the Palo Alto conference, Hinde and Harlow had a discussion on motherhood and after returning home Hinde informed Bowlby that Harlow was interested in Bowlby’s recent work on this subject (Stephen Suomi, personal communication, September 27, 2006; Karen 1994 ; Hrdy 1999 ; Blum 2002 ; Van der Horst et al. 2007 ).

Harlow and Bowlby Become Acquainted in 1957

It was just several months later that Bowlby and Harlow introduced themselves by letter. The written record of their relationship commenced with a letter dated August 8, 1957 in which Bowlby expressed his interest:

Robert Hinde tells me that you were interested in my recent paper when he showed it to you at Palo Alto and at his suggestion I am now sending you a copy. I need hardly say I would be most grateful for any comments and criticisms you cared to make. I shall be at the Center at Palo Alto from mid-September and will be preparing it for publication then. Robert Hinde told me of your experimental work on maternal responses in monkeys. If you have any papers or typescripts I would be very grateful for them. If there were a chance, I would try to visit you next Spring when I hope to be moving around U.S.A. (Bowlby in a letter to Harlow, August 8, 1957)

The paper which Bowlby sent to Harlow at the time was a draft of “The nature of the child’s tie to his mother” (Bowlby 1958 ). Harlow replied by return of post, thanking Bowlby for the paper, which he several years later (in a letter to Bowlby, March 25, 1959) would refer to as a “reference bible”:

[Y]our interests are (...) closely akin to a research program I am developing on maternal responses in monkeys. I certainly hope that you can pay a visit to my laboratory sometime during this forthcoming year. At the moment our researches are just getting underway, and I hope to use these materials for my American Psychological Association Presidential Address in September, 1958. This address will be the first formal presentation of these researches. (Harlow in a letter to Bowlby, August 16, 1957)

Mutual Referencing After 1957

It was only after the two men began corresponding in August, 1957, that they began referring to each other’s writings. A review of Bowlby’s publications from 1951–1957 (Bowlby 1951 , 1953 , 1957 ; Bowlby et al. 1952 , 1956 ; Robertson and Bowlby 1953 ) yields no mention of Harlow’s work. Likewise, we find no reference to Bowlby’s work in Harlow’s first developmental writings (Harlow 1957 ).

The early correspondence resulted in the planning of mutual visits and in the exchange of reprints. Footnote 2 Seven of Bowlby’s publications (Bowlby et al. 1952 , 1956 ; Bowlby 1958 , 1960a , b , c , 1961c ) have been found in Harlow’s reprint collection, in addition to two volumes on Attachment and Loss (Bowlby 1969/ 1982 , 1973 ). It is especially interesting to see Harlow’s notes jotted in the margins of Bowlby’s papers.

As a result of the interchange, the first reference to Harlow’s work appears in Bowlby’s work (Bowlby 1958 ). This paper was an expanded version of an address Bowlby gave before the British Psycho-Analytical Society on June 19, 1957. The paper is concerned with conceptualizing the nature of the young child’s tie to his mother, the dynamics which promote and underlie this tie. Bowlby described four alternative views found in the psychoanalytic or psychological literature at the time. He then went on to present his own theoretical perspective. He emphasized that his view was based on direct observation of infants and young children, rather than on retrospective analysis of older subjects as was the typical base for psychoanalytic theorizing at the time. Bowlby ( 1958 , p. 351) went on to state:

The longer I contemplated the diverse clinical evidence the more dissatisfied I became with the views current in psychoanalytical and psychological literature and the more I found myself turning to the ethologists for help. The extent to which I have drawn on concepts of ethology will be apparent.

The four then contemporary views he described were first of all the cupboard-love theory of object relations, according to which the physiological needs for food and warmth are met by the mother, through which the baby gradually learns to regard the mother as the source of all gratification and love. Secondly, primary object sucking, which states that the infant has a built-in need to orally attach to a breast and subsequently learns the breast is attached to the mother and then relates to her also. Thirdly, primary object clinging, according to which the infant has a built-in need to touch and cling to a human being, independent of food, but just as important. And finally, primary return-to-womb craving, which holds that the infant resents its removal from the womb at birth and wants to return there.

Bowlby then described his own hypothesis, one of much greater complexity and quite controversial at the time (Karen 1994 ; Hrdy 1999 ), as “Component Instinctual Responses”. He believed that five responses comprise attachment behavior—sucking, clinging, following, crying, and smiling—also acknowledging that many more may exist. He explained that his theory was “rooted firmly in biological theory and requires no dynamic which is not plainly explicable in terms of the survival of the species” (Bowlby 1958 , p. 369).

A main point of Bowlby’s argument was that no one response was more primary than another. He believed it was a mistake to emphasize sucking and feeding as the most important. Pointing out the inadequacy of human infant studies to date in terms of illustrating his hypothesis, Bowlby turned to observation of animals. It was in this context that Bowlby first cited Harlow’s research. He clearly used Harlow’s findings to undermine the psychoanalytic idea that all attachment develops through oral gratification. Harlow had specifically investigated the importance of clinging. Bowlby cited Harlow’s yet unpublished nonhuman primate data “on the attachment behaviour of young rhesus monkeys” (later published as Harlow 1958 ):

Clinging appears to be a universal characteristic of primate infants and is found from the lemurs up to anthropoid apes and human babies... Though in the higher species mothers play a role in holding their infants, those of lower species do little for them; in all it is plain that in the wild the infant’s life depends, indeed literally hangs, on the efficiency of his clinging response... In at least two different species (...) there is first-hand evidence that clinging occurs before sucking... We may conclude, therefore, that in sub-human primates clinging is a primary response, first exhibited independently of food. Harlow (...) removed [young rhesus monkeys] from their mothers at birth, they are provided with the choice of two varieties of model to which to cling and from which to take food... Preliminary results strongly suggest that the preferred model is the one which is more ‘comf[ortable]’ to cling to rather than the one which provides food. (Bowlby 1958 , p. 366)

Harlow and Bowlby Finally Meet in 1958

After the first two letters in August, 1957, eight additional letters were exchanged during the period Bowlby spent at the Palo Alto Center from mid-September, 1957 through mid-June, 1958. In these letters, the two men discussed their mutual interests and made arrangements for Bowlby to visit Harlow’s lab in Madison as Bowlby was finally able to carry out the plans of a visit he had mentioned in his first letter. Bowlby attended one of Harlow’s lectures on April 26, 1958 and visited his laboratory for two days in June of that same year (Zazzo 1979 ). In a letter to his wife Bowlby shows his enthusiasm after their first encounter:

You may remember I went to hear the final paper of the [Monterey] conference—an address by Harry Harlow of Wisconsin on mother infant interaction in monkeys. His stuff is a tremendous confirmation of the Child’s Tie paper, which he quoted. Afterwards Chris[toph Heinicke] heard him remark, in very good humour, to a friend: “You know, I thought I had got hold of a really original idea [and] then to find that bastard Bowlby had beaten me to it!” This is not really true [and] I think we can say it’s a dead heat—[and] the work of each supports the other. We had a very aimable chat [and] arranged to meet in June. (Bowlby in a letter to Ursula, April 28, 1958; AMWL: PP/BOW/B.1/20) Footnote 3

The lecture Bowlby attended was a presentation Harlow gave at the meetings of the American Philosophical Society (published as Harlow and Zimmermann 1958 ) on the development of affectional responses in infant monkeys. There Harlow touched upon, in contrast with Bowlby’s earlier in-depth analysis of the same matter, the various psychoanalytic theoretical positions concerning the bond of the infant to the mother. Referring to their personal contacts, Harlow (Harlow and Zimmermann 1958 , p. 501) mentioned that “Bowlby has given approximately equal emphasis to primary clinging (contact) and sucking as innate affectional components, and at a later maturational level, visual and auditory following”. This was Bowlby’s first appearance in a Harlow publication.

Bowlby visited Madison in June, 1958 and wrote to Harlow on the 26th, thanking him for his hospitality, and adding: “I shall look forward to keeping in touch (...). I hope too you will put me on your list to send mimeograph versions as and when your stuff goes further forward. We will reciprocate.” By June of 1958, the earlier formal salutations and closings “Dear Professor Harlow” and “Yours sincerely” or “Dear Dr. Bowlby” and “Cordially” had changed to a much more informal tone, becoming “Dear Harry” and “Yours ever, John”, or “Dear John” and “Best personal wishes, Harry”.

Two months later, on August 31, 1958, Harlow delivered his famous presidential address on “The nature of love” to the American Psychological Association . “The recent writings of John Bowlby” are mentioned in the published paper (Harlow 1958 , p. 673), to the effect that he recognized the mother’s importance in providing the infant with intimate physical contact, as well as serving as a source of nutrition. Harlow also positively mentioned Bowlby’s notion of ‘primary object following’, i.e. the tendency to visually and orally search the mother. The fact that Bowlby is mentioned twice in the presidential address is of some significance given that Harlow mentions but six names of researchers and hardly discusses their ideas.

Ethology Further Emphasized in Bowlby’s Work

It was in July, 1959, that Bowlby ( 1960c ) read a paper on ethology before the Congress of the International Psycho-Analytical Association in Copenhagen. Bowlby began his paper by remarking that eight years had now passed since his interest in ethology had been aroused, initially by Lorenz’s gosling work.

From this time forward the further I read and the more ethologists I met the more I felt a kinship with them. Here were first-rate scientists studying the family life of lower species who were not only making observations that were at least analogous to those made of human family life but whose interests, like those of analysts, lay in the field of instinctive behaviour, conflict, and the many surprising and sometimes pathological outcomes of conflict... A main reason I value ethology is that it gives us a wide range of new concepts to try out in our theorizing. (Bowlby 1960c , p. 313)

At the same time, Bowlby was cautious about extrapolating or generalizing from one species to another. He shared this restraint with Harlow who often reiterated that “monkeys are not furry little men with tails.” Both, however, were convinced of the importance of animal research in providing a better understanding of human social behavior. Bowlby ( 1960c , p. 314) expressed his view thus:

Man is a species in his own right with certain unusual characteristics. It may be therefore that none of the ideas stemming from studies of lower species is relevant. Yet this seems improbable. (...) [W]e share anatomical and physiological features with lower species, and it would be odd were we to share none of the behavioural features which go with them.

Carrying the notion further, Bowlby explained his efforts to use ideas gleaned from ethology in order to understand the ontogeny of what psychoanalysts called ‘object relations’. For a specific example of instinctual response systems present in the young, which facilitate the attachment of the infant to a mother figure without the mother’s active participation, Bowlby ( 1960c , p. 314) referred to and cited Harlow’s surrogate mother research: “a newborn monkey will cling to a dummy provided it is soft and comfortable. The provision of food and warmth are quite unnecessary. These young creatures follow for the sake of following and cling for the sake of clinging.”

Several pages later, in discussing the consequences of disrupting the mother–infant bond, Bowlby mentioned the substitution of one behavior for another due to frustration when the normal event was blocked, e.g., thumb sucking or overeating when denied maternal access. He drew a parallel with nonnutritive sucking in chimpanzees and rhesus monkeys:

In Harlow’s laboratory I have seen a full-grown rhesus female who habitually sucked her own breast and a male who sucked his penis. Both had been reared in isolation. In these cases what we should all describe as oral symptoms had developed as a result of depriving the infant of a relationship with a mother-figure... May it not be the same for oral symptoms in human infants? (Bowlby 1960c , p. 316)

In his conclusions, Bowlby once again stated that an understanding of biological processes is required in order to understand the psychological concomitants of biological processes. Two months later, in September, 1959, the first symposium organized by Bowlby was held at the Tavistock Clinic and Harlow was an invited participant.

Mutual Contacts: the Ciba-symposia from 1959 to 1965

The initial introduction by Hinde and Bowlby’s visit to Harlow’s laboratory led to a fruitful cooperation during the following years. Just prior to a Chicago meeting, Harlow invited Bowlby to visit the University of Wisconsin again, but Bowlby replied with regrets on March 30, 1961, stating that he was already booked up with engagements relative to a forthcoming Chicago trip and would hope to visit Harlow’s lab in 1962 or 1963 during a “more leisurely trip in the States. Looking forward to seeing you in the Autumn” (Bowlby in a letter to Harlow, March 30, 1961). Bowlby was undoubtedly referring to the second of four so-called Ciba-symposia Footnote 4 to be held in London in the fall of 1961.

The Ciba-symposia followed the design for interdisciplinary discussion Bowlby had first experienced during the meetings of the WHO on the psychobiological development of the child, which he attended in the early 1950s (Tanner and Inhelder 1971; cf. Foss 1969 ). Bowlby was impressed by the series’ innovative format: the meetings brought together a small group of researchers from different countries and disciplines for the purpose of promoting the knowledge of the subject matter and enhancing a mutual understanding of each other’s work and views.

Thus, following this model, Bowlby convened and chaired the Tavistock study group on mother–infant interaction, a series of four meetings at two-year intervals, held in the house of the Ciba foundation in London between 1959 and 1965. Harlow was a major participant of and contributor to the Ciba-symposia in 1959 (Harlow 1961 ), 1961 (Harlow 1963 ), and 1965 (Harlow and Harlow 1969 ), but was unable to attend the third session in 1963. In his introduction to the proceedings of the last meeting, Bowlby contended that his early hopes had come true:

As the series of meetings proceeds, reserves and misconceptions, inevitable when strangers from strange disciplines first meet, will recede and give place to an increasing grasp of what the other is attempting and why; to cross-fertilization of related fields; to mutual understanding and personal friendship. (Bowlby in Foss 1969 , p. xiii)

It is clear that both Harlow and Bowlby shared these positive feelings about the effectiveness of the symposia and that Bowlby was very pleased with the way things worked out. During the second study group, on September 7 and 9, 1961, Bowlby wrote to his wife Ursula:

There is widespread enthusiasm at the way the study group is going, regrets we have so little time, [and] shows demand we meet again in [two] years time—(after our holiday next time). The atmosphere is much less tense this time—Jack Gewirtz no longer a problem child—[and] communication is quick, spontaneous [and] effective. The two year gap, I’m sure, is better than one year. It has given plenty of time for everyone to digest the lessons of the first meeting, [and] there has been much private visiting [and] private communication between the members since. The result is that this time it is the atmosphere of a house-party. Harry H[arlow] has got to London last night so missed the first two days but is now with us. (...) Tomorrow he is on the platform [and] we should probably have some firework. I confess I feel rather proud of this party, both as a convener [and] chairman, I can take much credit for the party atmosphere, [and] also because so much of the work reported owes its origin to my stimulation. We have had [three] excellent presentations (Mary Ainsworth, Peter Wolff [and] Heinz Prechtl) [and] two that were too long (Jack Gewirtz [and] Tony Ambrose). In addition, Robert [Hinde] has shone [and] Rudolf Schaffer did very well in a brief contribution. They say Thelma [Rowell] is on the best of things [and] presents her Cambridge monkeys tomorrow. (Bowlby in a letter to Ursula, September 7, 1961; AMWL: PP/BOW/B.1/24)

The study group is over [and] has been a tremendous success. Everyone has enjoyed it [and] feel they have profited from it. It has been extremely friendly [and] intense, together with cautious and effective discussion. We managed to cover a lot of ground without hurry. It is striking how far [and] fast people have developed in the two years since we last met. In a sense it has become a kind of club [and] seems likely to have far reaching effects. (Bowlby in a letter to Ursula, September 9, 1961; AMWL: PP/BOW/B.1/24)

After the last of the Ciba-symposia, Bowlby wrote to Harlow that he was “very glad indeed that you were able to be with us last week and to give us such a stimulating account of your work” (Bowlby in a letter to Harlow September 21, 1965). Bowlby’s sentiments concerning the ultimate success of the four-part series are echoed in a letter Harlow wrote to Bowlby:

It was my personal opinion that the last [Ciba-symposium] was more informative than the first two. (...) I was impressed by the fact that the people who reported both in formal papers and in discussion were far more sophisticated about the problems (...) and I think I can include myself within this generalization. Furthermore, I thought that members of the conference communicated with each other far more effectively than they had (...) and I believe that this was a result of increasing sophistication in the nature of the problems attacked and in the development of adequate measurement and techniques. I personally believe that the Tavistock series (...) achieved a great deal. (Harlow in a letter to Bowlby, October 18, 1965)

There is no doubt, then, that the Ciba-symposia achieved their goal. By bringing together major figures in the field, such as Mary Ainsworth, John Bowlby, Jack Gewirtz, Harry Harlow, Robert Hinde, Harriet Rheingold, and Theodore Schneirla, they were able to further the mutual understanding of animal psychologists, ethologist, and learning theorists, and to advance the understanding of infant behavior (Foss 1961 , 1963 , 1965 , 1969 ). In particular, they allowed Bowlby and Harlow to meet on a regular basis and to discuss each other’s ideas thoroughly.

Bowlby’s Writings in the Early 1960s: Using Harlow’s Empirical Findings as a Secure Base

In the early 1960s, in several papers, Bowlby ( 1960a , b , 1961a , b , c ) expanded upon the theme of separation anxiety. He intended it as a corollary to his earlier treatise on the child’s tie to the mother (Bowlby 1958 ). In a review of the literature (Bowlby 1961a ; cf. Bowlby 1960a ), he presented his new conceptualization of separation anxiety in the same detailed manner as he elaborated on the nature of the child’s tie to the mother in that previous paper. Before presenting his own theory, Bowlby delineated five different theories of anxiety related to the child’s attachment to the mother. First, he described ‘transformed libido’ theory, a view held by Freud until 1926, where he attributed anxiety to a child’s unsatisfied libido upon separation from an attachment figure. Second, he mentioned the view that separation anxiety may mirror birth trauma and is the counterpart to the craving of the infant in the ‘return-to-the-womb theory’ met before. The third view Bowlby discussed was that of ‘signal theory’, which held that anxiety behavior has a function and results from a safety device to ensure that the separation will not be long and implied that the child’s tie to the mother derives from a secondary drive. The fourth view presented was that of ‘depressive anxiety’, after Melanie Klein, who suggested the infant felt responsible for destroying his mother and believed he had lost her forever. Finally, Bowlby discussed ‘persecutory anxiety’, also after Melanie Klein, where the young child feels the mother has left him, because she is angry with him.

Bowlby then described his own theory as ’Primary anxiety’ theory, defining anxiety as:

a primary response not reducible to other terms and due simply to the rupture of the attachment to his mother. / The child is bound to his mother by a number of instinctual response systems, each of which is primary and which together have high survival value (...) I wish to distinguish it sharply from states of anxiety dependent on foresight. (Bowlby 1961a , pp. 253 and 267)

Bowlby ( 1960a ) emphasized that his theory involved a new and ethologically inspired approach:

The heart of this theory is that the organism is provided with a repertoire of behaviour patterns, which are bred into it like the features of its anatomy and physiology, and which have become characteristic of its species because of their survival value to the species [original italics]. (Bowlby 1960a , p. 95)

But Bowlby now also clearly relied on the careful experiments by comparative psychologists such as Harry Harlow. In discussing fright and an animal’s escape from a fearful situation to a secure situation, he referred to the latter as a “haven of safety”, a term which he took from Harlow and Zimmermann ( 1958 ). Bowlby quoted Harlow and Zimmermann as follows:

In describing their very interesting experiments with rhesus monkeys they write: ‘One function of the real mother, human or sub-human, and presumably of a mother surrogate, is to provide a haven of safety for the infant in times of fear or danger.’ (Bowlby 1960a , p. 97)

Later in the same paper, Bowlby compared the behavior of the young child, Laura (filmed by Robertson 1952 ), who pretended to be asleep when a strange man entered her room, to the behavior of the rhesus infants, who froze in a crouched posture when introduced to a strange situation in the absence of the surrogate mother. That remarkable comparison too was a reference to Harlow and Zimmermann’s paper. Bowlby also discussed the infants’ rushing to the mother (if she was present) as a source of security, describing the response as so strong “it can be adequately depicted only by motion pictures” (Bowlby 1960a , p. 101). He was no doubt referring to Harlow’s film, The nature and development of affection (Harlow and Zimmermann 1959a ), a film that has been shown to thousands of introductory psychology classes over the years and received an award for excellence at a European film festival in 1960.

In three other papers Bowlby ( 1960b , 1961b , c ) of that period discussed maternal separation and the processes of grief and mourning: according to his views separation from the mother-figure would lead to separation anxiety and grief and would set in train processes of mourning. Bowlby described the three stages of protest, despair and detachment. One of the papers was based on a lecture Bowlby ( 1961c ) read at a meeting of the American Psychiatric Association in Chicago in May, 1961. There Bowlby once again presented his new ideas to an audience of psychiatrists. He stressed the importance of observation instead of using retrospective evidence, described the analogous course of grief and mourning in children and adults as well as in animals, and finally pointed to the evolutionary basis of the process of mourning. To buttress his claim that “In the light of phylogeny it is likely that the instinctual bonds that tie human young to a mother figure are built on the same general pattern as in other mammalian species” (Bowlby 1961c , p. 482), Bowlby referred once again to the work of Harlow (Harlow and Zimmermann 1959b ). There was no discussion of Harlow’s work beyond that, but Bowlby’s own description of the stages of protest, despair and detachment was to greatly influence Harlow’s experimenting.

Harlow’s Research in the 1960s: Seeking Empirical Evidence for Bowlby’s Theoretical Claims

Bowlby’s influence on Harlow’s work becomes evident after the first two Ciba-conferences. In two studies on mother–infant separation Harlow modeled his experiments with rhesus monkeys on the human separation syndrome described by Bowlby (Stephen Suomi, personal communication, August 27, 2006). In his experiments Harlow either physically (Seay et al. 1962 ) or totally (not just physically but also visually and audibly) separated (Seay and Harlow 1965 ) the infant rhesus monkeys from their mothers for three and two weeks respectively. In both studies, the rhesus infants initially responded with “violent and prolonged protest” and then passed into a stage of “low activity, little or no play and occasional crying”. These stages were similar to the phases of protest and despair described by Bowlby. The third phase of detachment was not found in either study, presumably because of the relatively short period of separation. Overall, Harlow reported considerable similarity in the responses to mother–infant separation in human children and infant monkeys, explicitly referring to Bowlby’s ( 1960b , 1961a ) studies on the subject.

Bowlby’s Continuing Interest in Harlow’s Work

Ten years after their first publications on the mother–child bond (Bowlby 1958 ; Harlow 1958 ), Bowlby ( 1968 ) published a paper on the effects on behavior of the disruption of an affectional bond. In this paper he stated that “[t]here is now abundant evidence that, not only in birds but in mammals also, young become attached to mother-objects despite not being fed from that source...”, and referred to Harlow’s work with rhesus monkeys (Harlow and Harlow 1965 ). This statement made clear that there no longer was any empirical support for psychoanalytic and learning theorist explanations for attachment behavior.

In 1969, four years after the fourth and last Ciba-symposium, the first volume of Bowlby’s trilogy on Attachment and Loss was published. In that volume, Bowlby draws heavily on the results of Harlow’s experiments as an empirical confirmation of his ideas. Throughout this book, Bowlby makes ample use of animal evidence and biological theorizing (e.g., Lorenz, Tinbergen). Among the students of animal behavior Bowlby referred to, Harlow figured prominently. We shall mention but a few examples.

In discussing motor patterns of primate sexual behavior, Bowlby (1969/ 1982 , p. 165) claimed there is clear evidence that they are subject to a sensitive developmental phase and pointed out Harlow’s extensive series of experiments in which rhesus infants were raised in differing social environments, “all differing greatly from the environment of evolutionary adaptedness”. Pointing out the deficits in adult heterosexual behavior displayed by the Wisconsin isolate-reared monkeys, Bowlby cited a personal communication in which Harlow wrote he was “now quite convinced that there is no adequate substitute for monkey mothers early in the socialization process” (Harlow in a letter to Bowlby dated October 18, 1965).

A chapter on the nature of attachment behavior contained a reiteration by Bowlby (1969/ 1982 , p. 178) of the four principal theories of the child’s tie to the mother that he had disputed in his earlier paper (Bowlby 1958 ). This time he prefaced his own view with the interesting phrase: “Until 1958, which saw the publication of Harlow’s first papers and of an early version of the view expressed here, four principal theories regarding the nature and origin of the child’s tie were (...) found.” With that phrase, Bowlby seemed to at least implicitly make two points: first, that he and Harlow simultaneously and independently arrived at similar views, and, second, that Harlow’s findings were of fundamental importance for attachment theory and hence for his own thinking.

In a discussion of primate infant and mother roles in their joint relationship, Bowlby (1969/ 1982 , p. 194) referred to the tenacity of primate infants brought up in human homes to cling to their foster parents and added: “Of the cases in which an infant has been brought up on an experimental dummy the best-known reports are those of Harlow and his colleagues (Harlow 1961 ; Harlow and Harlow 1965 ).” The next sub-topic (Bowlby 1969/ 1982 , p. 195) was the infant’s ability to discriminate the mother, and Bowlby again cited Harlow and Harlow ( 1965 ) pointing out that Harlow believed a rhesus infant learned attachment to a specific mother during the first week or two of life.

In his chapter on the nature and function of attachment behavior, Bowlby connected Lorenz’s work on imprinting to Harlow’s rhesus monkey work. To support his views on the nature and function of attachment behavior, Bowlby (1969/ 1982 , pp. 213–216) used Harlow’s experiments to undermine “the secondary drive type of theory”. He meticulously described Harlow’s (Harlow and Zimmermann 1959b ; Harlow 1961 ) experiments with the cloth and wire mother illustrating “that ’contact comfort’ led to attachment behaviour whereas food did not” and that “typical attachment behaviour is directed to the non-feeding cloth model whereas no such behaviour is directed towards the feeding wire one”.

In developing a control systems approach to attachment behavior, Bowlby (1969/ 1982 , p. 239) applied Harlow’s (Harlow and Harlow 1965 ) views on the object and social exploratory behavior of young monkeys to that of human children: just as infant monkeys, human children have an exploratory system that is “antithetic to [their] attachment behaviour”, because it takes them away from their mother.

From these few examples, it becomes clear that in the first volume of his magnum opus Attachment and Loss , Bowlby used Harlow’s empirical data on rhesus monkeys as uncontested evidence for his own views on the nature and development of the attachment relation which is formed between children and their caregivers in the first year of life. Harlow’s findings provided Bowlby with independent empirical evidence, which he could use to argue the superiority of his ideas over and above those of psychoanalysts and learning theorists.

In this contribution, we have taken a closer look at the cross-fertilization of the work of John Bowlby and Harry Harlow. We have demonstrated Harlow–Bowlby ties through correspondence and mutual presence at professional meetings. They wrote dozens of letters and met at least five times between 1958 and 1965. Instances in which Bowlby cited Harlow’s work in order to make a point, or as illustrative documentation of a behavior or phenomenon, have been noted. We may conclude that Harlow’s scientific influence on Bowlby has been demonstrated beyond reasonable doubt: Harlow’s experiments showed in a remarkable way what Bowlby had been theorizing about since his introduction to ethology in the early 1950s. Our findings make abundantly clear that Singer ( 1975 ) was completely wrong in asserting that Harlow’s findings had no impact on Bowlby’s theory whatsoever. A careful analysis shows that Harlow provided an important part of the solid empirical foundation for Bowlby’s theoretical construction.

In his turn, Harlow was influenced by Bowlby’s new theorizing. We have described how in two studies on separation (Seay et al. 1962 ; Seay and Harlow 1965 ) Harlow modeled his experiments on Bowlby’s ideas. Harlow’s own assertion that he and his colleagues used one of Bowlby’s paper as something of a “reference bible” (see above), his frequent requests in their correspondence for offprints of Bowlby’s papers, and his references to Bowlby’s ideas make it clear that he regarded Bowlby as one of the major theoreticians. It was Harlow’s student Suomi ( 1995 ) who acknowledged Bowlby’s major influence in three areas of animal research: (1) descriptive studies of the development of attachment and other social relationships in monkeys and apes, (2) experimental and naturalistic studies of social separation in nonhuman primates, and (3) investigations of the long-term consequences of differential early attachments in rhesus monkeys.

The scientific and personal contact between Bowlby and Harlow that started in 1957 lasted through the 1960s and early 1970s until Harlow’s retirement in 1974. They kept each other informed about their work and cited each other’s work extensively. Although they came from widely diverging backgrounds and differed in many respects they found a common denominator in their interest in the origin of affectional bonds. Together they reached the introductory psychology textbooks and influenced the lives of many children around the world.

The correspondence between Harry Harlow and John Bowlby (thus far twenty letters were recovered) resides with Helen A. LeRoy.

Note that reprints at the time had to be typed anew, because the Xeroxing machine was still a luxury of the future. In order to make multiple copies to exchange their writings, researchers had to resort to having papers typed several times or to reproducing them by mimeograph. On the mailing list for Harlow’s papers we find among others the names of Mary Ainsworth, Gerard Baerends, John Bowlby, Julian Huxley and René Spitz.

AMWL stands for Archives and Manuscripts, Wellcome Library for the History and Understanding of Medicine, 183 Euston Road, London NW1 2BE. The letters PP/BOW stand for Personal Papers Bowlby.

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van der Horst, F.C.P., LeRoy, H.A. & van der Veer, R. “When Strangers Meet”: John Bowlby and Harry Harlow on Attachment Behavior. Integr. psych. behav. 42 , 370–388 (2008). https://doi.org/10.1007/s12124-008-9079-2

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DOI : https://doi.org/10.1007/s12124-008-9079-2

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Rigorous Experiments on Monkey Love: An Account of Harry F. Harlow’s Role in the History of Attachment Theory

2008, Integrative Psychological and Behavioral Science

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Harry Harlow's pit of despair: Depression in monkeys and men

Lenny van rosmalen.

1 Centre for Child and Family Studies, Leiden University, Leiden The Netherlands

Maartje P. C. M. Luijk

2 Department of Psychology, Education & Child Studies, Erasmus University Rotterdam, Rotterdam The Netherlands

Frank C. P. van der Horst

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Major depressive disorder is the most common mood disorder in the United States today and the need for adequate treatment has been universally desired for over a century. Harry Harlow, famous for his research with rhesus monkeys, was heavily criticized when he undertook his controversial experiments trying to find a solution for depression in the 1960s–1970s. His research, however, did not just evolve gradually from his earlier research into learning and into love. Recently disclosed hand‐written notes show, for the first time, the severity of Harlow's depressions as he wrote in detail about his feelings and thoughts during his stay in a mental hospital in 1968. In these notes, Harlow repeatedly vowed to put every effort into finding a cure for depression. This may, for a large part, explain why he did not stop his rigorous animal experiments where critics argue he should have, and he eventually managed to book positive results.

Depression or complete despair Is life devoid of cause or care Denying wish, or hope or feel , A life within a wall of steel Harry F. Harlow 1

2. INTRODUCTION

The American psychologist Harry Frederick Harlow (1905–1981) belongs to the most well‐known psychologists of the 20th century (Haggbloom et al.,  2002 ). Working with baby rhesus monkeys and artificial mothers created from different materials, he found that baby monkeys prefer a nonfeeding soft cloth mother providing physical comfort and warmth over a wire mother providing only milk. This appeared to prove that babies have a need for love which is unconnected to their need for food, as attachment theorists were already claiming. Harlow's account of this study in an article called “The nature of love” (1958) has been cited more than 4200 times in the scientific press, has become a standard item of psychology textbooks, captured the attention of experts of wide‐ranging disciplines such as the history of science (Haraway,  1989 , 2005 ; Vicedo,  2009 , 2010 , 2013 ), psychotherapy (Slater,  2004 ), primatology (Arcus,  2016 ), and scientific journalism (Blum,  2002 ,  2011 ; Tavris,  2014 ). It was even told in the form of a cartoon (Ottaviani,  2007 ) and overall stirred the imagination of the general public. He had firmly placed himself on the map as the scientist who had discovered “The nature of love”. However, Harlow's previous work on learning and later work on depression, although (briefly) discussed by some of the aforementioned experts, is generally much less well‐known. The existing discussions on Harlow's depression research generally regard his experiments as controversial or unnecessarily cruel but fail to provide the backdrop against which Harlow operated: the state of depression research at the time and the urgency he felt to find a solution after experiencing severe depression himself. In this article, we will fill this gap.

Even though knowledge about depression has increased over the past century, according to the World Health Organization in 2021, 5% of adults suffer from depression, which means 280 million people are affected (WHO,  2021 ). The progress of treatment possibilities has been slow, regularly distracted by hiccups and controversial experiments. When Harlow suffered his major depression in 1968, there were no clear‐cut solutions to this affliction. He had already done some research into depression, but after his stay in a mental hospital, the Mayo Clinic in Rochester, Minnesota, in 1968 he shifted his focus completely to studying depression. As he did so, however, Harlow's research methods became increasingly questionable (Gluck,  1997 ). He considered experiments with monkeys (“nonhuman animals”) justified as he believed that the findings could be generalized to humans (“human animals”) (Harlow et al.,  1972 ; Harlow & McKinney,  1971 ), and so Harlow had no qualms about trying to create depression in rhesus monkeys, in order to then try to cure them. Animal rights activists, their voices being heard properly for the first time, justly protested against his methods. We argue that one of the main reasons for Harlow's perseverance was his own experience with depression at a time when no satisfying treatment was available. Different from his research into learning—which he chose to do out of interest—and his research into love—which more or less accidentally followed as part of his ongoing research—Harlow's research into depression was strongly driven by his personal experiences.

Giving an overview of Harlow's career from the beginning, we create the necessary background against which to view his research choices, in particular the choices he made regarding his depression research. Even though Harlow had suffered from bouts of depression throughout his adult life, his major depression in 1968 appears to be a turning point. Recently disclosed handwritten notes 2 from Harlow's personal archives, presented for the first time in this article, provide a unique insight into his feelings and thoughts before, during, and after his stay at the Mayo Clinic. The notes sketch a particularly bleak period in Harlow's life and add strong personal motives for trying the utmost to find a solution for depression. His research during this last part of his career contained rigorous methods that many considered unethical. Harlow, we will show, was nevertheless convinced of its necessity, and managed to book positive results in the end.

3. RESEARCH INTO LEARNING

Harry Harlow, born Harry Frederik Israel in 1905, received his PhD from Stanford University in 1930 and joined the University of Wisconsin that same year as an assistant professor of psychology. His intention was to study psychological behavior in rats but the lack of a decent laboratory forced him to move his observations to the local Vilas Park Zoo in Madison, where he studied the behavior of primates (lemurs, monkeys, and apes). Harlow was surprised at their intelligence, which led to a program of primate learning research (see, e.g., Harlow,  1932 ; Harlow & Settlage,  1934 ; Harlow et al.,  1932 ; Harlow & Yudin,  1933 ; Maslow & Harlow,  1932 ; Yudin & Harlow,  1933 ). When testing the primates on learning and memory, existing tests that were normally used with other animals like pigeons, rats, or dogs turned out to be far too simple and Harlow developed the Wisconsin General Test Apparatus (WGTA), which contained an array of learning and memory tasks (Harlow & Bromer,  1938 ). The WGTA soon became the standardized intelligence test for primates (Sidowski & Lindsley,  1989 ). Together with his brother Robert Israel, a psychiatrist and head of the Warren State Hospital, Pennsylvania, he compared the test results of monkeys and apes to those of human subjects (Harlow & Israel,  1932 ).

When a suitable building became available on the Wisconsin campus in 1932, Harlow moved his research from the local zoo to his own primate laboratory (of which he remained director until his retirement in 1974) and his subjects changed from larger primates to mainly rhesus monkeys. Advancing their research into learning, in the late 1930s Harlow and his students began to try and locate areas in the brain responsible for specific intellectual processes in monkeys. Much like Karl Lashley ( 1950 ), they would alter the brain surgically and then observe the difference in behavior to understand where “learning” was situated (Harlow,  1939 ; Harlow & Dagnon,  1943 ; Spaet & Harlow,  1943a , 1943b ). Altering the brain surgically was experimented with in different fields at this time. Treatment for depression, for instance, was attempted through frontal lobotomy or leucotomy (Kucharski,  1984 ). These procedures, which involved severing connections in the prefrontal cortex, were regularly executed in the USA between 1935 and 1955. However, Harlow was not yet involved in this—he would not start his research into depression until the second half of the 1960s.

Harlow and his students continued to study problem solving in monkeys through various methods (see, e.g., Harlow,  1943 , 1944a , 1944b ; Harlow & Poch,  1945 ; Simpson & Harlow,  1944 ; Spaet & Harlow,  1943a , 1943b ; Young & Harlow,  1943a , 1943b ; Zable & Harlow,  1946 ). When researching intelligence in primates, Harlow moved away from Clarke Hull's ( 1943 ) ideas on drive reduction. According to drive reduction theory, primates are motivated by drifts and will perform a task if the reward is food to satisfy their hunger. On closer scrutiny, however, the primates appeared not to be primarily motivated by hunger, but instead by curiosity. Even without food as a reward, they would try to solve the puzzles put in front of them (see Figure  1 ). Feeding before the testing actually improved performance in many cases (Davis et al.,  1950 ; Harlow et al.,  1950 ; Moss & Harlow,  1947 ). In addition, Harlow discovered how primates learned to learn, which he called “learning sets” (Harlow,  1949 ). He was the first to demonstrate that animals (monkeys) are capable of abstract thinking, research important enough to lead to Harlow becoming the first psychologist to be elected member of the National Academy of Sciences in 1951 (Gluck,  1997 ; “Lab Notes,” Harlow's personal papers). His 1949 study on learning sets has been cited more than 2800 times, making it his second most cited article (after The nature of love, 1958).

Young rhesus monkeys in a test situation

4. RESEARCH INTO LOVE

During the 1950s Harlow's Primate Lab was expanded a few times to house the growing colony necessary for studying the development of learning in monkeys from birth onwards. Harlow's shift from studying learning to studying love—or, to be more precise, social relationships in primates—was more or less serendipitous (cf. Callahan & Berrios,  2005 ). An outbreak of tuberculosis in Harlow's laboratory in 1955 caused him to lose almost his entire colony of rhesus monkeys. To prevent this from happening again, Harlow started to separate baby monkeys from their mothers 12 h after birth and placed them in separate cages to prevent contamination of disease. This did indeed prevent diseases from spreading, but as a result, the baby monkeys started to exhibit strange and pathological behavior (Sidowski & Lindsley,  1989 ). Presumably looking for a substitute for the motherly warmth they were lacking, the baby monkeys clung to the towel cloth that was covering the bottom of their cages. Harlow's friend and colleague from the United Kingdom, John Bowlby, pointed out during a visit to the Primate Lab in 1958 that this behavior was probably the result of the lack of mother‐love (Suomi et al.,  2008 ; Van der Horst et al.,  2008 ; Van Rosmalen et al.,  2020 ). Bowlby, who would become famous for developing attachment theory together with Mary Ainsworth (Van Rosmalen et al.,  2016 ), was trained in psychoanalysis. He would, however, challenge psychoanalytical ideas after studying the relationship between (human) mothers and their children for decades. He had specifically been studying the effect of separation experiences, where children were separated from their mother for a longer period through hospitalization, war evacuation, and so forth (cf. Bowlby,  1952 , 1958 , 1959 , 1961 ). Bowlby's meeting with Harlow would strengthen their understanding of the effects of separation and they would refer to each other's work (Van der Horst et al.,  2008 ), even though Harlow would move away from some of Bowlby's ideas later on in his career (Vicedo,  2009 , 2010 ).

Intrigued by the monkeys' behavior Harlow created his now world‐famous surrogate monkey mothers made of cloth and put them next to surrogate mothers made of metal wire, the latter ones providing milk through a feeding bottle. Contrary to popular belief and going against the so‐called cupboard‐love theory (stating that an infant loves his mother primarily as the result of her supplying food), the monkeys preferred the contact comfort of the soft cloth nonfeeding mother over the cold, metal, feeding one (Harlow,  1958 ; Harlow & Zimmermann,  1959 ). The need for warmth and bodily contact appeared to be innate. Again, Harlow's findings contradicted conventional ideas in psychoanalysis and drive reduction theory (Suomi et al.,  2008 ). When he was elected President of the American Psychological Association for 1958, Harlow's presidential address, “The nature of love,” consisted of the findings of this study and caused widespread publicity.

By this time, Harlow had become one of the most popular professors at the University of Wisconsin. Helen LeRoy, Harlow's assistant from 1958 onwards, describes him as down to earth, unassuming, and with a great sense of humor (LeRoy,  2008 ; personal communication, May 5, 2018; Suomi & Leroy,  1982 ). Following the enormous interest in artificial mother studies, Harlow's research changed focus and turned from learning to social development in monkeys. Initially, Harlow was enthusiastic about his artificial mother findings and even suggested that real mothers could possibly be replaced by surrogate mothers (Vicedo,  2009 ). However, once the monkeys that had been raised by artificial mothers became adults, they turned out to be mentally disturbed. They did not interact sexually with other monkeys, and females that became mothers after being impregnated were abusive to their young (Harlow,  1961 ; Seay et al.,  1964 ). Somehow, the monkeys reared by surrogate mothers lacked elementary social skills.

When continuing his experiments, Harlow started to suspect that it was not the surrogate mothers who were to blame, but the fact that the monkeys had had no contact with other monkeys whatsoever. This led to an increased interest in the effects of different social environments—from smaller to larger social groups consisting of adults, adolescents, and infants (Harlow & Harlow,  1965 ). These studies led Harlow to posit what he called affectional systems: “the idea that each monkey develops specific social relationships with its mother, its peers, its sexual partners, and eventually, with its own offspring” (“Lab Notes,” Harlow's personal papers). The effects of the different affectional systems were compared with the effects of growing up socially isolated. The consequences of the monkeys being deprived of social contact were all too obvious and seemed similar to what Bowlby ( 1952 ) and Spitz ( 1945 , 1946 ) had found in deprived children in hospitals and orphanages: physical care alone was not enough to grow up psychologically healthy (Figure  2 ).

Mother raised by surrogate with a young infant monkey

As Harlow continued to study the social causes of psychopathology, he simultaneously became increasingly interested in finding solutions. To enable him to experiment with different cures, however, he first had to find ways to systematically induce psychopathology or depression in his monkeys. Investigating the subject of depression may seem far removed from investigating the subject of love, but for Harlow, these were two sides of the same coin. He noted that “depression rarely leads to love, but love frequently leads to depression as we all know” (“The autobiography of a laboratory,” undated manuscript, Harlow's personal papers). Convinced of the importance of mother love, to induce depression he experimented with “evil” artificial mothers (see Figure  3 ): one that would shake to try and get the baby off, one which comprised a hidden catapult that would throw off the infant unexpectedly, one that blasted the baby monkey away with compressed air, and one which had hidden spikes that would appear suddenly.

“Evil” artificial mothers

Even though these evil surrogate mothers temporarily disturbed the infants, the disturbance did not last (Harlow et al.,  1971 ). Familiar with the research on the effects of mother–child separation, Harlow tried to induce depression through social isolation (Harlow et al.,  1966 ; Harlow & McKinney,  1971 ; Seay et al.,  1962 ; Seay & Harlow,  1965 ). This turned out to have stronger effects, especially when age‐mate or peer separation was used—Harlow had found that the peer affectional system was of great importance for healthy development, maybe even more so than the mother–child bond (Harlow & Harlow,  1965 ; cf. Vicedo,  2010 ). By the late 1960s, Harlow finally managed to induce depression by totally isolating monkeys from their mothers and peers (Harlow et al.,  1965 , 1964 ; Suomi et al.,  1970 ). The monkeys were now ready to help Harlow try to find ways to resolve the induced psychopathology. This cycle, which Harlow referred to as “Love created, love destroyed, and love regained” (“Lab history,” Harlow's personal papers), emphasizes his view of a close connection between love and depression.

But while Harlow's career was booming, his private life was at an all‐time low. In 1967 his (second) wife Margaret was diagnosed with breast cancer, and in 1968 Harlow suffered from a major depression which caused him to be committed to the Mayo Clinic for psychiatric treatment. During his stay on the ward he corresponded with his wife and with his brother Robert, and after being discharged he wrote down his experiences. The hand‐written notes start with a prelude to the depression, continue to describe in detail how he felt during his stay at the clinic, and give a thorough insight into Harlow's thoughts and feelings during his depression and treatment. Harlow, a scientist in heart and soul, apparently considered these experiences important enough to describe them extensively and intimately, and they clearly spurred him on to continue his research into adepression on his return, determined to find a solution.

5. “MAN IN A MADHOUSE” 3

Harlow had suffered from minor short‐term depressions throughout his life, but usually, they would last for no more than a few days. “When my moods swing toward gaiety I feel ‘wealthy' and secure, and when they swing toward depression I become convinced that I will die after long lingering poverty” (Harlow in a letter to his brother Delmer Israel, January 6, 1970). Strangely enough, even though Harlow was enormously successful in the academic world, one of the triggers for these short‐term depressions would be the winning of awards—the recurring thought that this would be the last ever scientific honor he might be awarded caused Harlow to be depressed:

I was obsessed by the idea that I would lose the “creative touch” that had enabled me to achieve the last one and that this was the end of my scientific career… When I was elected president of my scientific society 4 I was depressed for some days…

However, Harlow never thought of himself as being “mentally disturbed” and could not see himself being hospitalized for anything related to his depressions. He often used to whisper “I wish I were dead” although he quickly added that in reality, he suspected that he had no real wish to die. Even though Harlow claimed that “I did not believe I would ever really shoot myself unless I became depressed when intoxicated,” he described at length the ways he would commit suicide if he decided to do so:

The way I would achieve it was by shooting a .35 caliber revolver bullet, hopefully through my midbrain… An overdose of sleeping pills has always seemed to me as a socially accepted way to achieve euthanasia… A combination of C 2 H 5 OH and sodium amytal 5 or any other relatively long‐active barbiturate is an effective way of looking into the future—particularly when you don't believe you have one anymore.

Probably linked to these bouts of depression, as a coping strategy, Harlow had developed a drinking problem that had progressively become more serious over the years. He describes this extensively in his notes and tells of two occasions in which he drank too much, took sleeping pills, and collapsed unconscious on the floor. Both times, his children found him and called for help, and he was taken to hospital by ambulance.

At the age of 62, Harlow's worst depression set in after winning “the most significant national award that can be given in America” (i.e., National Medal of Science in 1967, presented at the White House by President Lyndon B. Johnson). In that same period, Harlow was trying to prepare a presentation on “Depression in subhuman animals” he had agreed to give at the National Institutes of Health. For a year he had put off its preparation, but he was not concerned, because he felt he was, “like many others, a confirmed procrastinator.” However, some weeks before the actual presentation Harlow found himself increasingly incapable of outlining the speech, reading the necessary literature, and assembling the slides. He started to show the external physical symptoms of depression, like walking slowly and talking to fewer people. His anxiety about the speech was growing. Harlow's wife Margaret tried to urge him to pick himself up but to no avail. He became more and more depressed, and in the end, he had what he called “a little nervous breakdown” but what turned out to be a depression serious enough for Harlow to be committed to hospital.

In March and April 1968, Harlow was treated for depression at the Mayo Clinic. Some of his notes describe his stay, the staff, and the way he spent his days. Harlow mentions “… the adverse effects of social isolation, but this has been a historical blind spot for physicians…” He was decidedly unhappy with the activities organized by the clinic: “Since I disliked all or almost all of the events which the hospital arranged to fill up time, the minutes, hours and days dragged on infinitely monotonously.” He did not think group therapy was beneficial at all and stated that “one of the few advantages of being on the closed ward lay in the fact that all of the patients in the open ward were being subjected [five] days a week to group therapy sessions,” which seemed to Harlow to cause them to “become more deeply depressed.” Of the group therapy he had to take part in every other day he said he

thoroughly believed, and [sic] did most of the patients, that it was a mistake… I never saw group therapy conducted by an expert but it seemed to me that it was a combination of nondirected therapy and an attempt to get the patients to reply to two standardized questions: “How do you feel?” and “How do you relate to other people?” If Mayo had created a third question I never heard it in 2 months.

More important to Harlow was the frequent correspondence with his wife, who wrote to him almost daily. Harlow himself would write when he was able—sometimes one or more long letters in 1 day, at other times he did not manage to write for days.

After 2 weeks Harlow was told that he would have to undergo a treatment of electroconvulsive shock therapy (ECT). This worried Harlow, because he was “an anti‐[ECT] 6 advocate and believe[d] that there [wa]s not enough scientific knowledge about [ECT] to justify using it except as a condition of desperation.” In the late 1930s and early 1940s, the first reports on the effects of electroshock were published (e.g., Cerletti,  1938 ; Kalinowsky & Barrera,  1940 ; cf. Rzesnitzek,  2015 ) and showed that inducing seizures (as had been done before with insulin shock to treat schizophrenia) could relieve symptoms of affective disorders such as depression. ECT became one of the prominent treatment methods in the 1950s and 1960s. However, Harlow had been an editor for the Journal of Comparative and Physiological Psychology for 12 years and been on the editorial board of Science . During that time, of the more than 50 papers on the subject of ECT, only 2 that dealt with human subjects were accepted for publication, both of which were subsequently retracted by the authors. Nevertheless, since his personal physician, the Mayo staff, his wife, and his brother Robert, who himself was a psychiatrist by training, all thought ECT would be best for him, he “submitted as best [he] could.” Being a scientist, he naturally considered the available research:

Also, in deference to the intellectual demands of my profession, they gave me unilateral [ECT] treatments instead of bilateral treatments… Before entering the hospital I had read the two best and most recent psychiatric reports of the effects of unilateral versus bilateral [ECT] treatments. One of the papers was so badly planned and presented that I was surprised to see it published in a journal of clinical medicine. The other paper was much better but the measures used to determine cortical hemispheral dominance were naïve and the statistical treatment of the data left much to be desired, even though my knowledge of statistics leaves much to be desired. I doubt if either of the papers would have been accepted by a really scientific journal.

After receiving the ECT treatments Harlow nevertheless admitted that recovery was generally good and looking back on it he stated: “I am convinced that my own treatment gave me transient help. It made the early days of hospitalism more endurable.”

After 59 days at the Mayo Clinic Harlow returned home (Figure  4 )

Harry and Margaret in the Primate Lab

6. RESEARCH INTO DEPRESSION

Even though it is often suggested that Harlow's 2 months at the Mayo Clinic instigated his depression research (Blum,  2002 ), it was actually set in motion well before then. His social deprivation studies (e.g., Harlow,  1964 ) had led to experimenting with inducing depression in monkeys through social isolation, and the presentation he was trying to prepare leading up to his own depression was titled “Depression in subhuman animals.”

From Harlow's personal notes, we now know that he had suffered from bouts of depression for as long as he could remember, but it was specifically his major depression in 1968 which strongly increased his efforts to find a solution. In his notes he stated:

There may be some forms of mental illness in which the staff or family suffer more than the patient but I doubt that this can be true when the patient is in deep depression and one assumes that the staff and family are not themselves critically ill at the same time. One of my few motivations to recover during the darkest hours was to have a chance to tell the world how deeply the patient had suffered… I hoped to partially recover so that I would tell the world about the agonies that a depressed person undergoes. I can say that the mental torment of depression is extreme…

Remembering a textbook description of depression, Harlow said: “The man who wrote these charmingly objective words never underwent a true depression himself. These are just words put on paper and do not convey the hours of endured torment.” That Harlow felt a deep need to find a solution also becomes clear from an undated manuscript from Harlow's personal papers, titled “Depressions: Facts or Fantasies” in which he stated:

The outlook of most people who have a psychotic depression is grim but for about 5% (?) the outlook is not grim but grave because they will find surcease and sorrow in suicide, and the percentage of recovery from a well‐planned suicide is negligible… Depression has been recognized as a clinical syndrome for over 2,000 years which is a long time to find out nothing about a disease entity… essentially nothing so far has been achieved and everything remains to be done. In part, this will be obtained by the use of human subjects and in part by subhuman subjects as stable, psychotic positions may be instituted into them.

As Harlow correctly pointed out, the treatment possibilities were only developing very slowly. Until the 1940s medical doctors viewed mental illness as irreversible. As a result, most doctors chose to use sedative‐hypnotics such as barbiturates or bromides to treat depression (Callahan & Berrios,  2005 ). An alternative for the use of sedative‐hypnotics was frontal lobotomy or leucotomy (Kucharski,  1984 ), used between 1935 and 1955, followed by ECT in the 1950s and 1960s (which would fall into disrepute by the mid‐1970s).

Another problem, apart from the slow speed at which treatment possibilities were being explored, was the confusion about the diagnostic criteria for depression, with as many as 12 different classification systems in place (Kendell,  1976 ). Only from the 1980s, and the publication of DSM‐III were experts beginning to make sense of what we now conceptualize as “depression,” which caused the current, more scientific, and medical treatment paradigm to be installed. This paradigm involves the four pillars of criteria‐based diagnosis, measures of severity of illness, articulation of a biomedical framework, and a better understanding of the epidemiology of affective and emotional disorders (Callahan & Berrios,  2005 ).

According to Harlow, in the late 1960s, only time (“if the hospital staff can keep the patient from suicide for a reasonable period of time there is a good chance that the patient will recover”), ECT, and the recently discovered antidepressant drugs were available to possibly (partly) alleviate depression. Even though he felt ECT had helped him along the road to recovery, he considered the scientific evidence to be meager, and the antidepressant drugs still had too many side effects. He felt there was a lot of work to be done, especially in the area of therapeutic techniques, which he knew worked in some cases of other human psychotics (Harlow et al.,  1972 ).

As Harlow intensified his research into depression, he looked for valid and rigorous study designs. To him, it was clear that humans and monkeys showed enough parallels in their normal social development to be able to draw important conclusions from monkey research (Harlow et al.,  1965 ; Harlow & McKinney,  1971 ; Seay et al.,  1964 ). When designing his research, Harlow did not first create an experiment in monkeys to then determine if the results could be generalized to humans but worked the other way around: he would start with data obtained from humans and see if they could be replicated in monkeys. As his first and third wife, Clara Mears Harlow ( 1986 ) stated:

The monkey, and especially the rhesus monkey, gave clear evidence of being able to replicate many human behaviors. This fact was of the utmost importance since it solidified and established the formula used by Harlow in his experiments: if human behavior could be replicated in the monkey, the results of the study would generalize to human behavior (p. xxii).

According to Harlow, animal studies into depression would be of enormous interest to clinicians, especially:

1) the nature of the bonds that, when broken, lead to depression; 2) the kinds of separation experiences that in themselves are most likely to lead to depression; 3) the effect of age on the response to separation; and 4) the effects of reunion at varying stages of separation (McKinney et al.,  1971 , p. 1319).

Even though Harlow was convinced that many biologically trained scientists would agree with him that generalization from nonhuman behavioral data to man was justifiable (Harlow et al.,  1972 ), he felt the addition of clinical psychiatrist William McKinney to the Primate Center in 1969 to be of enormous value. According to Harlow, he brought “clinical insight and psychiatric respectability” (Harlow et al.,  1971 ). The combination of scientists studying animals in a laboratory and clinicians observing human patients causes reinforcement and greater understanding on both sides (Löwy,  2003 ). McKinney had previously published on depression research in animals (McKinney & Bunney,  1969 ) and would become one of the driving forces behind the depression research at the Primate Center in the early 1970s (Helen LeRoy, personal communication, October 18, 2007).

Harlow, together with Stephen Suomi, who at the time was working as a research assistant to Harlow, had been experimenting with different apparatuses designed to produce depression in monkeys. The Quad Cage (see Figure  5 ) was a combined experimental living cage where the animals could be repetitively isolated by sliding in various types of screens, but it took at least 6 months to induce depression this way. To speed up the process, they designed the much‐criticized pit of despair and the tunnel of terror. When the monkeys were subjected to total isolation for about 30 days in a vertical chamber (called the pit of despair; see Figure  6 )—a stainless steel trough, the sides of which sloped down inwards to prevent the monkeys from climbing up to the open‐top—it was enough to induce depression (Harlow & Suomi,  1971b ,  1974 ; Harlow et al.,  1970 ; Suomi & Harlow,  1969 , 1972a ). About the pit, Harlow and Suomi wrote:

Depressed human beings report that they are in the depths of despair or sunk in a well of loneliness and hopelessness. Therefore, we built an instrument that would meet these criteria and euphemistically called it the pit, or the vertical chamber for those who find the term “pit” psychologically unacceptable (Suomi & Harlow,  1969 , p. 247).

It is clear that the vertical chamber has enormous potential for rapid production of psychopathological behavior in monkeys… While we did not ask our subjects if they felt helpless and/or hopeless, their posture and lack of activity seemed to indicate an attitude of “giving up” (Harlow & Suomi,  1971a , p. 253).

Quad Cage: A living cage designed to induce depression

Vertical chamber or pit of despair

Harlow confirmed that “all three human developmental stages described by Spitz and Bowlby unfolded in infant monkeys” (Harlow et al.,  1972 ; McKinney et al.,  1973 ). The tunnel of terror, which could be used in combination with the pit of despair, consisted of a tunnel in which something scary like a battery‐powered toy robot would be moving towards the monkey to intensify depression.

Animal protection activists justly protested against the use of these apparatuses, but the animal rights movement had not quite come into its own as yet—the Laboratory Animal Welfare Act had only recently passed in 1966, and the movement would not be clearly heard until the late 1970s, after publications like Richard Ryder's Victims of science (Ryder,  1975 ) and Peter Singer's ( 1975 ) Animal Liberation , placing speciesism next to racism and sexism (Franco,  2013 ). Nevertheless, even though animal research for medical purposes was still considered morally acceptable by the majority of the public, criticism grew as Harlow continued his experiments. At the same time, the overall treatment of the monkeys in Harlow's Primate Lab was considered to be above contemporary standards for laboratory animals (Blum,  2002 ; Helen LeRoy, personal communication, May 5, 2018), which may have made it easier for those involved to justify the rigorous experiments. When Harlow received letters from the public, criticizing his research, he would always write back communicating his reasons:

[M]y brilliant and beloved wife, Dr. Margaret Harlow, lost a long hard battle with cancer. Cancer probably causes almost as much human suffering as depression, and I would certainly be opposed—adamantly opposed—to blocking medical research in either of these areas. I believe the long‐term goal to alleviate human suffering justifies the utilization of subhuman animals in trying to find cures. I would like to emphasize the fact that we employ the most humane measures possible in caring for our animals… I believe we are sincerely interested in working toward the resolution of human problems (Harlow in a letter to A. C. Whitaker, November 11, 1971).

The experiments using the vertical chamber were also criticized from within the scientific community (as a result of which Suomi and Gluck later distanced themselves from this type of research). However, in his articles Harlow also explained how he felt justified using these controversial methods: “The theoretical linkages between monkey and human psychopathology, including psychoses in childhood, merit exploration” (Harlow & Suomi,  1971a , p. 254); and “Depression destroys more people than any other disease entity. With subhuman help depression may be eradicated” (Harlow & Suomi,  1971c , “Generalization of behavior from men to monkeys,” Harlow's personal papers, p. 3). Mary Ainsworth, in a discussion of papers by Suomi and Bowlby, stated that

it is evident that, with a few minor exceptions, there is such a striking congruity between the findings for human and nonhuman primates in regard to responses to separation and to the subsequent reunion that it can only be gratifying to all who have devoted time and energy to the explorations relevant to this problem (Ainsworth,  1976 , p. 40).

The real objective, of course, was to find successful treatments for induced depression. Different treatments were considered, including ECT and antidepressant drugs (Harlow et al.,  1971 ). However, apart from Harlows' personal reservations, by this time ECT was falling into disrepute. Antidepressants were becoming the standard treatment method in combination with psychotherapy, but the success of the use of antidepressants such as iproniazid and imipramine (from the 1950s), lithium, monoamine oxidase inhibitors, and chlorpromazine (from the 1970s) was helped much by pharmaceutical companies that successfully used marketing strategies to make their products the predominant psychotropic medication in a “therapeutic vacuum” (Callahan & Berrios,  2005 ). Chlorpromazine was tried in some monkeys but as soon as the medication was stopped, abnormal behaviors came back. Some other antidepressants available at the time also did not have lasting effects (McKinney in an interview with T. A. Ban, 2001).

Harlow, having focused on relationships for decades, felt that too much attention was paid to antidepressant drugs, and research into therapeutic techniques to alleviate symptoms of depression was sorely lacking (Harlow et al.,  1972 ). He had not been enthusiastic about the type of group therapy he himself had received at the Mayo Clinic but was nevertheless drawn to the idea that social relationships could alleviate depression. Harlow, therefore, started focusing on social manipulation—initially reversing the isolation process which had induced the depression. In the beginning, Harlow was pessimistic (Harlow & Novak,  1973 ). In a letter, he wrote:

We have studied the effects of extremely deprived environments on the social, sexual, and maternal behavior of monkeys, and we have found that such deprivation maintained for the first six months of life or longer completely destroys the monkey as a social animal—and destroys it forever. We doubt very much if any remedial process would be of avail, although we intend to make some small effort to find out within the next year (Harlow in a letter to Jessie Crane, Educational Coordinator of Head Start, June 9, 1969).

Not long after, however, he was relieved to be able to admit that he had been wrong: “[We have] successfully rehabilitated a group of 6‐month total social isolates and… 12‐month total isolate monkeys. Since I had stated for a long time that rehabilitation of these monkeys was impossible, I was both chastened and educated” (in a letter to Betty Flint, University of Toronto, May 16, 1974). Harlow and Suomi (later joined by Novak) found that monkeys could be (partly) cured of depression by joining them with so‐called therapist monkeys—socially and mentally healthy monkeys that were younger than the depressed monkeys (Harlow,  2019 ; Harlow & McKinney,  1971 ; Harlow & Suomi,  1971a ; Suomi & Harlow,  1972b ). The age difference was considered important because same‐age peers had been seen to exhibit aggressive behavior towards monkeys raised in isolation (Harlow et al.,  1965 ). Harlow had previously seen infants of motherless mothers endlessly struggle to try and contact their dysfunctional mothers—maybe young monkeys would show the same behavior towards older depressed peers. It worked: the young therapist monkeys were joined with the depressed monkeys most days a week for a few hours and would approach the depressed monkey and cling to it, from time to time attempting to play at an elementary level (Figure  7 ). The depressed monkeys initially just huddled in a corner but after a while reciprocated the clinging. In due course, the depressed monkeys joined in playing, and later still, initiated play. Eventually, the (formerly) depressed monkeys appeared to behave relatively normally (Novak,  1979 ; Novak & Harlow,  1975 ; Suomi et al.,  1976 ; Suomi & Harlow,  1972b ; Suomi et al.,  1972 , 1974 ). According to Harlow, “this rehabilitation method was successful and may provide experimental support for the group treatment of some childhood psychotic states” (Harlow & McKinney,  1971 ). Harlow felt that, because depression was induced as an early experience in the monkey, this meant that reversal of psychopathological behavior might generalize to humans whose depression had been caused by inadequate early experience like trauma after separation (Suomi & Harlow,  1972b ; Young et al.,  1973 ). He was excited about

the implications for the process of therapy that these data raise… that social recovery can be achieved in subjects whose social deficits were once considered irreversible… and by the nature of the therapeutic procedure itself (Suomi et al.,  1972 , p. 931).

Patient and therapist in clinging position

Harlow was now becoming increasingly optimistic about the development of therapeutic techniques for treating depression in people by the generalization of the research findings to human therapists: “The psychotherapeutic principles of avoidance of social fears and the inculcation of gradual stepwise social interaction will doubtless eventually be discovered by the psychiatrists” (“The autobiography of a laboratory,” undated manuscript, Harlow's personal papers). In his experiments, Harlow clearly showed the importance and therapeutic effect of social relations (Vicedo,  2010 ). Harlow considered both social relations and the understanding, accepting attitude of the monkey therapists important aspects of the successful treatment of depression, which he hypothesized to be helpful in the treatment of deprived or depressed infants and children (Blum,  2002 ; Harlow in Analysis Analyzed, undated manuscript, Harlow's personal papers). Responding to the controversy around his research, he would later state that:

If you're going to work with love you're going to have to work with all of its aspects. Some of the work is in a sense cruel, but remember for every mistreated monkey there exist a million mistreated children. If my work will point this out and save only one million human children, I can't get overly concerned about 10 monkeys. Besides, we successfully rehabilitated our depressed monkeys anyway. The techniques are probably applicable to human beings (August 3, 1978, The Capital Times P.M ., Madison, WI).

Today, general guidelines for the treatment of depression in adolescents and adults 7 suggest a combination of pharmacotherapy and psychotherapy (American Psychological Association,  2019 ). According to these APA guidelines, the first choice for psychotherapeutic treatment is either cognitive behavioral therapy (CBT) or interpersonal psychotherapy (IPT). CBT is a psychosocial intervention that includes the behavioral activation of a patient into his social environment, much like Harlow's monkeys were thrust back into the social environment. IPT is attachment‐focused psychotherapy that concentrates on resolving interpersonal problems and is based on the idea that healthy relationships affect mood. Just as Harlow's experiments had shown, therapists can teach victims of depression to have better social relations.

With the encouraging results of the therapist monkeys, Harlow felt he was finally getting some answers:

In our study of psychopathology, we began as sadists trying to produce abnormality. Today we are psychiatrists trying to achieve normality and equanimity. …Three years ago the idea of using monkeys to unravel the behavioral and biochemical intricacies of an affliction suffered in some form, and at some time, by virtually every human being and fully understood by no human mind, seemed to be little more than a desperate dream or humble hope. Today we are finally and firmly on the road to success (Harlow et al.,  1971 , p. 548).

Margaret Harlow died of cancer in 1971, and in 1972 Harlow remarried his first wife, Clara Mears. Harlow formally retired from the University of Wisconsin in 1974 but continued to coauthor publications on the subject of depression for some years. His research was continued by Suomi and colleagues.

7. CONCLUSION

In this paper, we focused on a lesser‐known but nevertheless heavily criticized period in Harry Harlow's research career: his study of depression and its possible cure. Depression has affected many for centuries, and the need for adequate treatment is universally desired. However, the progress of treatment possibilities has been slow over the past century, moving through trial and error, from sedation to lobotomy or leucotomy, followed by ECT and later still, medication combined with psychotherapy. While Harlow's interest in studying depression had started well before his hospitalization, his search intensified after his own experience of severe depression. The severity of his feelings and his proposed determination to find a cure for depression become clear from recently disclosed hand‐written notes. Harlow is famous for his research into “love,” but the last part of his career included cruel experiments that appeared to be far removed from love. For Harlow, however, love and depression were merely two sides of the same coin—take love away and one finds depression. Having felt the gravity of a major depression himself caused him to disregard any criticism against his rigorous experiments which he felt were needed to find a solution at a time when science had not managed to come up with an effective treatment for depression, and eventually Harlow managed to book some positive results. Considering Harlow's own experience of depression combined with the lack of a proper solution at the time adds a different angle from which to view the cruel experiments Harlow undertook to find a cure for what he called “a life within a wall of steel.”

ACKNOWLEDGMENT

This study was made possible by grants awarded to the first and third author by the Köhler‐Stiftung (no. S112/10210/16) and the Dr. J. L. Dobberke Stichting voor Vergelijkende Psychologie (no. 3819).

Rosmalen, L. , Luijk, M. P. C. M. , & Horst, F. C. P. (2022). Harry Harlow's pit of despair: Depression in monkeys and men . Journal of the History of the Behavioral Sciences , 58 , 204–222. 10.1002/jhbs.22180 [ PMC free article ] [ PubMed ] [ CrossRef ] [ Google Scholar ]

1 Undated manuscript from Harlow's personal archives; Harry Harlow Papers, Harlow Primate Laboratory, University of Wisconsin‐Madison, Madison, WI.

2 These notes were recovered from the Harry Harlow Papers, Primate Laboratory, University of Wisconsin‐Madison, Madison, WI, and were made available to us by Harlow's former assistant Mrs. Helen LeRoy. We are grateful to Mrs. LeRoy for her assistance and hospitality.

3 This is the title of one of Harlow's writings about his time at the Mayo Clinic; Harlow's personal archives, Madison, Wisconsin, USA.

4 Harlow was president of the APA, 1958–1959.

5 A combination of alcohol and barbiturates has led to many cases of suicide, including those of celebrities, especially before the introduction of benzodiazepines as an alternative (López‐Muñoz et al.,  2005 ).

6 Harlow used the then‐prevailing acronym “ECS” for electroconvulsive shock therapy. For reasons of clarity, we changed this to the currently used acronym “ECT.”

7 For treatment of child patients with depressive disorders there was insufficient evidence to make a recommendation (American Psychological Association,  2019 ).

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• Experiments

Harlow's Experiments on Attachment Theory

More painful experiments on attachment

Harlow wasn’t satisfied with what he had confirmed. He decided to go even further, without regard for the well-being of the rhesus monkeys. He isolated them in even smaller spaces where there was nothing but food and drink. That way, he could observe how they behaved in total isolation .

Many of the monkeys were trapped inside these chambers for months, and some even years. Deprived of all social and sensory stimulation, the monkeys started to show changes in their behavior as a result of their confinement. The monkeys that were confined for a year entered a catatonic state. They became passive and indifferent towards everyone and everything.

When the monkeys reached an adult age, they couldn’t properly relate to the other monkeys. They couldn’t find partners, felt no need to reproduce, and some even stopped eating and drinking. Many died.

To read the full-text of this research, you can request a copy directly from the author.

• CESK PSYCHOL
• Veronika Koutná
• Dalibor Vobořil

• Daniel Marston
• Terry Maple
• Sara Wadhwa

• Susan Mineka
• Stephen J. Suomi

• J CONSUM PSYCHOL

• SOC COGN AFFECT NEUR
• Sara B. Algoe

• Harry F. Harlow
• Howard S. Hoffman
• Alan M. Ratner
• J HIST BEHAV SCI

• Raymond J. McCall
• William Kessen

• Ashley Montagu
• Seymour L. Halleck

• Cillian Twomey
• Ruth Feldman
• EXP DERMATOL
• Donna M Lloyd

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• V Sterlemann

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