monkey isolation experiment

Harry Harlow Theory & Rhesus Monkey Experiments in Psychology

Saul Mcleod, PhD

Editor-in-Chief for Simply Psychology

BSc (Hons) Psychology, MRes, PhD, University of Manchester

Saul Mcleod, PhD., is a qualified psychology teacher with over 18 years of experience in further and higher education. He has been published in peer-reviewed journals, including the Journal of Clinical Psychology.

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Olivia Guy-Evans, MSc

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Olivia Guy-Evans is a writer and associate editor for Simply Psychology. She has previously worked in healthcare and educational sectors.

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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.

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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.

Before you continue, we thought you might like to download our three Positive Relationships Exercises for free . These detailed, science-based exercises will help you or your clients build healthy, life-enriching relationships.

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).

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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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 (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'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

Associated data.

Data sharing is not applicable to this article as no new data were created or analyzed in this study.

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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Harry Harlow Biography

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

Emily is a board-certified science editor who has worked with top digital publishing brands like Voices for Biodiversity, Study.com, GoodTherapy, Vox, and Verywell.

Career and Research

Influence on psychology, selected publications, recommended reading.

Harry Harlow was an American psychologist who is best-remembered for his series of controversial and often cruel experiments with rhesus monkeys where he placed infant monkeys in isolated chambers. In one review of the most eminent psychologists of the 20th century, Harlow was ranked 26th out of 100. His work contributed to the understanding of the importance of caregiving, affection, and social relationships early in life.

Birth and Death

• Harry Harlow was born on October 31, 1905, in Fairfield, Iowa.
• He died on December 6, 1981, in Tucson, Arizona.

Harry Harlow (born Harry Israel) grew up in Iowa. He attended Reed College in Portland, Oregon, for one year but, after passing a special aptitude test, he enrolled at Stanford University where he started out as an English major. His grades were so bad that after one semester he switched to the study of psychology.

While at Stanford, Harlow studied with psychologist Lewis Terman, who helped develop the Stanford-Binet intelligence test . In 1930, Harlow earned his Ph.D. in psychology. He later changed his last name from Israel to Harlow.

After graduating from Stanford, Harlow was offered a position at the University of Wisconsin-Madison. While at the school, he established the pioneering Primate Laboratory where he would perform his controversial social isolation experiments. Harlow's classic series of experiments were conducted between 1957 and 1963 and involved separating young rhesus monkeys from their mothers shortly after birth. The infant monkeys were instead raised by surrogate wire monkey mothers.

In one version of the experiment, one of the "mothers" was made entirely from the wire while the other was covered with a soft cloth. Harlow found that regardless of whether or not the cloth-covered mother provided food, the infant monkeys would cling to her for comfort. On the other hand, the monkeys would only select the wire mother when she provided food.

Harlow presented his results at the annual convention of the American Psychological Association in 1958 and also reported his findings in his classic article entitled "The Nature of Love" in the journal American Psychologist .

Later experiments looked at social isolation by raising rhesus monkeys either in total or partial isolation. Harlow and his students found that such isolation led to a variety of negative outcomes including severe psychological disturbances and even death.

Harlow's experiments were shocking and controversial. Most would be considered unethical by today's standards. However, his research played an important role in shaping our understanding of child development. Prevailing thought during Harlow's time suggested that paying attention to young children would "spoil" them and that affection should be limited. Harlow's work instead demonstrated the absolute importance of developing safe, secure, and supportive emotional bonds with caregivers during early childhood.

Many experts at the time also believed that feeding was the primary force between the mother-and-child bonds. Harlow's work suggested that while feedings are important, it is the physical closeness and contact that provides the comfort and security that a child needs for normal development. Harlow's work along with that of other researchers, including psychologist John Bowlby and pediatrician Benjamin Spock, helped spark a revolution in our approach to childcare and child-rearing.

• Harlow HF. The effect of large cortical lesions on learned behavior in monkeys. Science . 1950;112(2911):428.
• Harlow HF, Woolsey CN. Biological and Biochemical Bases of Behavior. University of Wisconsin Press; 1958.
• Harlow HF, Baysinger CM, Plubell PE. A variable-temperature surrogate mother for studying attachment in infant monkeys. Behavior Research Methods. 1973;5(3):269-272.
• Harlow HF. Lust, latency, and love: Simian secrets of successful sex. Journal of Sex Research. 1975;11(2):79-90.
• Harlow HF. The nature of love. American Psychologist. 1958;13:673-685.

Blum D. Love at Goon Park . New York: Perseus Publishing; 2002.

Harlow HF. The nature of love . American Psychologist . 1958;13:673-685.

Association for Psychological Science. Harlow’s classic studies revealed the importance of maternal contact .

Van Rosmalen L, van der Veer R, van der Horst FCP. The nature of love: Harlow, Bowlby and Bettelheim on affectionless mothers. Hist Psychiatry. 2020. doi:10.1177/0957154X19898997

Vicedo M. The evolution of Harry Harlow: from the nature to the nurture of love . Hist Psychiatry. 2010;21(2):190-205. doi:10.1177/0957154x10370909

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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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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These 1950s experiments showed us the trauma of parent-child separation. Now experts say they’re too unethical to repeat—even on monkeys.

By Eleanor Cummins

Posted on Jun 22, 2018 7:00 PM EDT

8 minute read

John Gluck’s excitement about studying parent-child separation quickly soured. He’d been thrilled to arrive at the University of Wisconsin at Madison in the late 1960s, his spot in the lab of renowned behavioral psychologist Harry Harlow secure. Harlow had cemented his legacy more than a decade earlier when his experiments showed the devastating effects of broken parent-child bonds in rhesus monkeys. As a graduate student researcher, Gluck would use Harlow’s monkey colony to study the impact of such disruption on intellectual ability.

Gluck found academic success, and stayed in touch with Harlow long after graduation. His mentor even sent Gluck monkeys to use in his own laboratory. But in the three years Gluck spent with Harlow—and the subsequent three decades he spent as a leading animal researcher in his own right—his concern for the well-being of his former test subjects overshadowed his enthusiasm for animal research.

Separating parent and child, he’d decided, produced effects too cruel to inflict on monkeys.

Since the 1990s, Gluck’s focus has been on bioethics; he’s written research papers and even a book about the ramifications of conducting research on primates. Along the way, he has argued that continued lab experiments testing the effects of separation on monkeys are unethical. Many of his peers, from biology to psychology, agree. And while the rationale for discontinuing such testing has many factors, one reason stands out. The fundamental questions we had about parent-child separation, Gluck says, were answered long ago.

The first insights into attachment theory began with studious observations on the part of clinicians.

Starting in the 1910s and peaking in the 1930s, doctors and psychologists actively advised parents against hugging , kissing, or cuddling children on the assumption such fawning attention would condition children to behave in a manner that was weak, codependent, and unbecoming. This theory of “behaviorism” was derived from research like Ivan Pavlov’s classical conditioning research on dogs and the work of Harvard psychologist B.F. Skinner , who believed free will to be an illusion. Applied in the context of the family unit, this research seemed to suggest that forceful detachment on the part of ma and pa were essential ingredients in creating a strong, independent future adult. Parents were simply there to provide structure and essentials like food.

But after the end of World War II, doctors began to push back. In 1946, Dr. Benjamin Spock (no relation to Dr. Spock of Star Trek ) authored Baby and Child Care, the international bestseller, which sold 50 million copies in Spock’s lifetime. The book, which was based on his professional observation of parent-child relationships, advised against the behaviorist theories of the day. Instead, Spock implored parents to see their children as individuals in need of customized care—and plenty of physical affection.

At the same time, the British psychiatrist John Bowlby was commissioned to write the World Health Organization’s Maternal Care and Mental Health report. Bowlby had gained renowned before the war for his systematic study of the effects of institutionalization on children, from long-term hospital stays to childhoods confined to orphanages.

Published in 1951, Bowlby’s lengthy two-part document focused on the mental health of homeless children. In it, he brought together anecdotal reports and descriptive statistics to paint a portrait of the disastrous effects of the separation of children from their caretakers and the consequences of “deprivation” on both the body and mind. “Partial deprivation brings in its train acute anxiety, excessive need for love, powerful feelings of revenge, and, arising from these last, guilt and depression,” Bowlby wrote. Like Spock, this research countered behaviorist theories that structure and sustenance were all a child needed. Orphans were certainly fed, but in most cases they lacked love. The consequences, Bowlby argued, were dire—and long-lasting.

The evidence of the near-sanctity of parent-child attachment was growing thanks to the careful observation of experts like Spock and Bowlby. Still, many experts felt one crucial piece of evidence was missing: experimental data. Since the Enlightenment, scientists have worked to refine their methodology in the hopes of producing the most robust observations about the natural world. In the late 1800s, randomized, controlled trials were developed and in the 20th century came to be seen as the “gold standard” for research —a conviction that more or less continues to this day.

While Bowlby had clinically-derived data, he knew to advance his ideas in the wider world he would need data from a lab . But by 1947, the scientific establishment required informed consent for research participants (though notable cases like the Tuskegee syphilis study violated such rules into at least the 1970s). As a result, no one would condone forcibly separating parents and children for research purposes. Fortunately, Bowlby’s transatlantic correspondent, Harry Harlow, had another idea.

Over the course of his career, Harlow conducted countless studies of primate behavior and published more than 300 research papers and books. Unsurprisingly, in a 2002 ranking the impact of 20th century psychologists , the American Psychological Association named him the 26th most cited researcher of the era, below B.F. Skinner (1), but above Noam Chomsky (38). But the (ethically-fraught) experiments that cemented his status in Psychology 101 textbooks for good began in earnest only in the 1950s.

Around the time Bowlby published WHO report, Harlow began to push the psychological limits of monkeys in myriad ways—all in the name of science. He surgically altered their brains or beamed radiation through their skulls to cause lesions, and then watched the neurological effect, according to a 1997 paper by Gluck that spans history, biography, and ethics. He forced some animals to live in a “deep, wedge-shaped, stainless steel chambers… graphically called the ‘pit of despair'” in order to study the effect of such solitary confinement on the mind, Gluck wrote. But Harlow’s most well-known study, begun in the 1950s and carefully documented in pictures and videos made available to the public, centered around milk.

To test the truth of the behaviorist’s claims that things like food mattered more than affection, Harlow set up an experiment that allowed baby monkeys, forcibly separated from their mothers at birth, to choose between two fake surrogates. One known as the “iron maiden” was made only of wire, but had bottles full of milk protruding from its metal chest. The other was covered in a soft cloth, but entirely devoid of food. If behaviorists were right, babies should choose the surrogate who offered them food over the surrogate who offered them nothing but comfort.

As Spock or Bowlby may have predicted, this was far from the case.

“Results demonstrated that the monkeys overwhelmingly preferred to maintain physical contact with the soft mothers,” Gluck wrote. “It also was shown that the monkeys seemed to derive a form of emotional security by the very presence of the soft surrogate that lasted for years, and they ‘screamed their distress’ in ‘abject terror’ when the surrogate mothers were removed from them.” They visited the iron maiden when they were too hungry to avoid her metallic frame any longer.

As anyone in behavioral psychology will tell you, Harlow’s monkey studies are still considered foundational for the field of parent-child research to this day. But his work is not without controversy. In fact, it never has been. Even when Harlow was conducting his research, some of his peers criticized the experiments , which they considered to be cruel to the animal and degrading to the scientists who executed them. The chorus of dissenting voices is not new; it’s merely grown.

Animal research today is more carefully regulated by individual institutions, professional organizations like the American Psychological Association and legislation like the Federal Animal Welfare Act. Many activists and scholars argue research on primates should end entirely and that experiments like Harlow’s should never be repeated. “Academics should be on the front lines of condemning such work as well, for they represent a betrayal of the basic notions of dignity and decency we should all be upholding in our research, especially in the case of vulnerable populations in our samples—such as helpless animals or young children,” psychologist Azadeh Aalai wrote in Psychology Today .

Animal studies have not disappeared. Research on attachment in monkeys continues at the University of Wisconsin at Madison . But animal studies have declined. New methods—or, depending on how you look at it, old methods—have filled the void. Natural experiments and epidemiological studies, similar to the kind Bowlby employed, have added new insight into the importance of “tender age” attachment .

Romanian orphanages established after the fall of the Soviet Union have served as such a study site. The facilities, which have been described as “slaughterhouses of the soul” , have historically had great disparities between the number of children and the number of caregivers (25 or more kids to one adult), meaning few if any children received the physical or emotional care they needed. Many of the children who were raised in these environments have exhibited mental health and behavioral disorders as a result. It’s even had a physical effect, with neurological research showing a dramatic reduction in the literal size of their brains and low levels of brain activity as measured by electroencephalography, or EEG, machines.

Similarly, epidemiological research has tracked the trajectories of children in the foster care system in the United States and parts of Europe to see how they differ, on average, from youths in a more traditional home environment. They’ve shown that the risk of mental disorders , suicidal ideation and attempts , and obesity are elevated among these children. Many of these health outcomes appear to be even worse among children in an institutional setting , like a Romanian orphanage, than children placed in foster care, which typically offers kids more individualized attention.

Scientists rarely say no to more data. After all, the more observations and perspectives we have, the better we understand a given topic. But alternatives to animal models are under development and epidemiological methodologies are only growing stronger. As a result, we may be able to set some kinds of data—that data collected at the expense of humans or animal —aside.

When it comes to lab experiments on parent-child attachment, we may know everything we need to know—and have for more than 60 years. Gluck believes that testing attachment theory at the expense of primates should have ended with Harry Harlow. And he continues to hope people will come to see the irony inherent in harming animals to prove, scientifically, that human children deserve compassion.

“Whether it is called mother-infant separation, social deprivation, or the more pleasant sounding ‘nursery rearing,'” Gluck wrote in a New York Times op-ed in 2016, “these manipulations cause such drastic damage across many behavioral and physiological systems that the work should not be repeated.”

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Harlow’s Rhesus Monkey Experiments

Harry Harlow, a prominent American psychologist, conducted a series of controversial experiments on Rhesus monkeys, beginning in the late 1950’s. Harlow’s research is a staple topic in introductory psychology texts. His findings corresponded with many of John Bowlby’s theories of attachment emerging during the same time. Harlow’s rhesus monkey experiments continue to have a profound impact on our understanding of social development, need for affection, and the importance of maternal care.

Key Definition:

Harry Harlow’s rhesus monkey experiments were a series of controversial studies on maternal separation and social isolation conducted in the 1950s and 1960s. Using rhesus monkeys, Harlow investigated the effects of maternal deprivation by separating infant monkeys from their mothers and subjecting them to varying degrees of social isolation.

In 1930, Harlow received his Ph.D. in psychology from Stanford University. He spent the remainder of his academic career as a professor at the University of Wisconsin—Madison ( Horst, et al., 2008 ). Harlow’s education was during a time that behaviorism dominated the college classrooms.

Harlow’s research aimed to investigate the nature of love, attachment, and social development in primates. Harlow saw love and affection as a neglected facet of human behavior. Harlow theorized that “the initial love responses of the human being are those made by the infant to the mother or some mother surrogate.” He further theorized that “from this intimate attachment of the child to mother, multiple learned and generalized affectional responses are formed” ( Harlow, 1958 ).

Harlow’s view of learned affectional responses coincides with John Bowlby’s theory of internal working models of relationship attachment. Robin Karr-Morse and Meredith Wiley explains this concept clearly in their writing, stating that “the child’s first relationship, typically with the mother, acts as a template for the imprinting of circuits in the child’s developing, emotion-processing right brain” ( Karr-Morse & Wiley, 2014. Kindle location: 911 ).

The basic underlying question these studies aimed to answer was “do infants have an innate need for mother love, or did they learn to love their mothers because mothers provided them with food?” ( Vicedo, 2010 ).

See Internal Working Models for more on this topic

The Rhesus Monkey

Harlow sought to understand the significance of early maternal separation and the effects of social isolation through experiments with infant rhesus monkeys. He explained that the macaque (rhuses) 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” ( Harlow, 1958 ).

Harlow chose to raise the monkeys from birth, he proclaimed that his bottle raised monkeys were physically healthier and heavier than the monkeys raised by their mothers. However, the experiments of varying social isolation had severe impacts on the behaviors of the rhesus monkeys. His findings on attachment, affection, and socialization are staples of early psychology. Modern ethics and moral standards disallow current studies to subject animals to these extremes.

Experiment Details

Harlow separated sixty infant rhesus monkeys from their mothers six to twelve hours after birth. They suckled the infant monkey’s on tiny bottles. harlow and his colleagues noticed that the infant monkeys showed strong attachment to the soft pads on the bottom of the cage. If experimenters pulled the young monkeys from the pads, the monkey would engage in a violent temper tantrum. Harlow therosed that the soft pads provided a sense of security. Perhaps, similar to a young child holding a security blanket or a stuffed animal to regulate stress.

Harlow designed experiments around offering the infant monkeys two surrogate “mothers.” They made one of wire and equipped it with a feeding bottle, and the other surrogate mother they covered in soft tan terry cloth. Harlow tried a variety of different variations of these two surrogate mothers. He tried the soft warm surrogate mother with and without a feeding apparatus. He observed the monkeys’ reactions and behaviors towards these surrogate mothers, aiming to discern the influence of comfort and food on the attachment behavior of the infants.

Surrogate Mother Preferences

A surprising and interesting early finding was that the young monkeys preferred the non-feeding, soft terry cloth surrogate mother over the wire feeding surrogate mother. “The monkeys spent most of their time with soft mother, regardless of which mother provided milk”( Vicedo, 2010 ). This opposed some early theories that suggested that infants bond to their mothers because the mother satisfies the basic needs of hunger and thirst. Basically, these theories posit that mom’s presence was associated with sustenance. The child bonded with mother through classical conditioning.

However, the infant monkey’s preference suggested that the soft surrogate mother provided an affectional need, independent of the milk. His studies provided support for the attachment need, underlying the need for both nursing and contact comfort.

Surrogate Mother and Security

To further the experiment, Harlow introduced the infant rhesus monkeys to a similar experiment as Mary Ainsworth’s strange situation . The infant monkeys responded in a similar fashion to the toddlers in the strange situation studies, utilizing their surrogate mothers as a secure base. “The baby monkeys reared with cloth mothers used the surrogate mother as ‘a source of security, a base of operations'” ( Vicedo, 2010 ). The monkeys with only a wire surrogate mother would also use the mother as a secure base. However, they never would leave her to explore objects.

To conduct this experiment Harlow placed several novel objects (a small artificial tree, a crumpled piece of paper, a folded gauze diaper, a wooden block and a doorknob) in a six feet by six feet room. Harlow reports that when the cloth mother was later placed in the room the baby monkeys would seek comfort from it. He wrote that “the infant would rush wildly to her, climb upon her, rub against her, and cling to her tightly.” However, if the mother was not placed back into the room the overwhelmed infants “would rush across the test room and throw themselves face downward, clutching their heads and bodies and screaming their distress” (Harlow, 1959, p. 78).

Harlow commented their conduct resembled “the autistic behavior seen frequently among neglected children in and out of institutions” ( Vicedo, 2010 ).

Early in Harlow’s studies he surmised that a real mother was unnecessary for emotional development. He saw the soft surrogate mother as an “eminently satisfactory mother.”

Adolescent Monkeys

While some of the early findings suggested that a surrogate mother could adequately replace a real mother, the adolescent and adult monkeys reared in isolation from other monkeys told a different story. Harlow wrote about the adult monkeys raised by surrogate mothers, “they are without question socially and sexually aberrant.” He continues, “the nourishment and contact comfort provided by the nursing cloth covered mother in infancy does not produce a normal adolescent or adult” (Harlow, 1966, p. 231).

The female monkeys that were artificially impregnated did not know how to mother their own babies. These monkeys were punitive mothers. “they rejected, abused and killed their infants. Harlow recanted his early suggestions that a real mother was dispensable. He wrote, “Apparently their early social deprivation permanently impairs their ability to form effective relations with other monkeys” (Harlow, 1966, p. 231).

Two Stages of Development

Harlow concluded that real mothers guided their children through two stages of development. During the first stage of development, the feral rhesus provided their offspring with sustenance and security (comfort contact). During the second phase, the mother literally pushes the child away so they can interact with other monkeys.

The surrogate mother adequately provided the infant with the developmental needs in stage one. However, these monkeys were deprived of the necessary developmental tasks encountered during phase two. The cage raised monkeys were “deprived of fathers, siblings, friends and all other family members of a social group” ( Vicedo, 2010 ).

Key Findings

The experiments yielded compelling results, demonstrating that the infant monkeys primarily sought comfort and security from the soft, cloth-covered surrogate mother, even when the wire mother provided nourishment. This emphasized the significance of emotional reassurance and physical contact in the formation of social attachments, challenging prevailing beliefs about the importance of nourishment in mother-infant relationships.

Contact Comfort

The need for human touch and physical contact is an essential aspect of our well-being. From the moment we are born, the comforting sensation of being held and touched plays a crucial role in our development. Research has shown that without adequate physical contact, especially during infancy and early childhood, individuals may experience impairments in their emotional, social, and cognitive development.

The act of being held and receiving physical affection from caregivers and loved ones creates a sense of security and attachment, allowing individuals to develop healthy relationships and emotional resilience. Through touch, our nervous system is activated, promoting the release of oxytocin, often referred to as the “love hormone,” which can reduce stress and anxiety while fostering a sense of trust and connection.

Furthermore, studies have indicated that the absence of physical touch can lead to adverse effects on both mental and physical health. Individuals who experience chronic deprivation of touch may be more susceptible to feelings of loneliness, depression, and anxiety. Additionally, the absence of touch has been linked to weakened immune function and heightened stress responses.

Ultimately, acknowledging and addressing the significance of physical touch in human development and well-being is critical. Creating environments and relationships that afford opportunities for meaningful touch and embraces can contribute to overall health and vitality, supporting individuals in leading fulfilling and balanced lives.

Affectional Systems

Harlow extrapolated from his research that primates have innate affectional systems. He posits that an individual’s different relationships do not simply arise from an extension of an infant’s love for its mother, but from developmental appropriate social exposures. These different systems translate into different forms of relationships. Such as mother-child, child-peer, infant-mother, and father-infant.

Affectional systems refer to the complex networks of relationships, emotions, and interactions that individuals have with others in their lives. These systems can include family members, friends, romantic partners, and even pets, and they play a crucial role in shaping an individual’s emotional well-being and social development. Affectional systems are essential for providing support, love, and a sense of belonging, and they contribute significantly to an individual’s overall happiness and resilience. Understanding and nurturing these different systems is important for maintaining healthy and fulfilling relationships.

Socialization

Harlow emphasized that proper emotional development requires more than a mother. Deborah Blum wrote “there’s a simple name for the next phase in building relationships. It’s called play and it’s one reason why it is so important that parents encourage their children to form friendships with peers.”

Children need play with peers for healthy development is a fundamental principle that underscores the importance of social interaction in the formative years of a child’s life. Engaging in play with peers not only fosters the development of crucial social skills such as communication, cooperation, and conflict resolution, but it also contributes to the overall well-being and emotional intelligence of a child.

Through play, children learn to navigate various social dynamics, understand boundaries , and cultivate empathy and understanding towards others. Furthermore, play with peers provides an avenue for children to express themselves, develop their creativity, and enhance their cognitive abilities through imaginative and collaborative activities. As such, creating opportunities for children to engage in play with their peers is essential in laying the foundation for healthy social, emotional, and cognitive development.

In reference to the monkeys in Harlow’s lab, Blum wrote, “as the monkeys grow older and play harder, they get better at sending and at reading the kind of messages that we call nonverbal communication. Peers tend to reinforce behaviors—reciprocating when they like an activity, ignoring or turning away when they don’t. So during play, you can also learn what makes your friends leave and how to coax them back” ( Blum, 2002 ).

Child Neglect

The Harlow’s monkey experiments are a haunting reminder of the profound effects of neglect on child development. These experiments, conducted by psychologist Harry Harlow, involved separating infant monkeys from their mothers and exposing them to two artificial surrogate “mothers” – one made of wire and the other covered with soft cloth. The monkeys consistently preferred the comforting cloth mother, even when the wire mother provided sustenance. This suggests that emotional comfort and attachment are essential for healthy development, and not just basic physical needs . The implications of these experiments are indeed deep and unsettling, shedding light on the crucial nature of emotional nourishment and care in early childhood. It serves as a stark reminder that children require not only physical sustenance, but also emotional support and nurturing to thrive and develop into healthy individuals.

Neuroscientists at Harvard University studied the cortisol levels of orphans who were raised in the dreadfully neglected child Romanian orphanages established during the Ceausescu regime. These institutions had a caregiver/child ratio of one caregiver for every twenty children. The children only received the basic the rudiments of care, seldom physically picked up or touched (comfort contact). Gabor Maté reports that “they displayed the self-hugging motions and depressed demeanour typical of abandoned young, human or primate.” Further research tested these orphaned children’s saliva discovering that “their cortisol levels were abnormal, indicating that their hypothalamic-pituitary-adrenal axes were already impaired” ( Maté, 2008, Kindle location: 3,609 ).

Basically, emotional neglect impacts the development of the brain.

Ethical Controversy

The experiments conducted by Harlow undeniably ignited intense ethical debates due to the evident psychological distress inflicted on the monkeys, sparking deep concerns and raising serious questions about the treatment of animals in research settings. The profound impact of these studies on the moral and ethical considerations of animal research cannot be overlooked. However, amidst these ethical controversies, it is crucial to recognize that Harlow’s research significantly contributed to our understanding of the critical role of early maternal care and social interactions in primate development. These insights have had a lasting influence on the field of psychology and continue to shape our understanding of human and animal behavior.

Legacy of Harlow’s Rhesus Monkey Experiments

Despite the ethical concerns surrounding his work, Harlow’s experiments revolutionized the field of psychology, highlighting the profound impact of social and emotional support on primate development. However, his findings have left an enduring legacy, shaping modern theories of attachment and influencing child-rearing practices.

Harlow’s Rhesus Monkey Experiments remain a contentious yet impactful chapter in the history of psychological research, underscoring the complex interplay of emotional, social, and physical needs in the formation of social bonds and relationships.

Last Update: February 20, 2024

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References:

Blum, Deborah ( 2002 ). Love at Goon Park : Harry Harlow and the Science of Affection. ‎Basic Books; 2nd edition.

Harlow, Harry ( 1958 ). The Nature of Love. American Psychologist, 13(12), 673-685. DOI: 10.1037/h0047884

Harlow, Harry ( 1959 ). The Development of Affectional Patterns in Infant Monkeys. Edited by D.M. Foss in Determinants of Infant Behavior: Proceedings of a Tavistock Study Group on Mother-Infant Interaction Held in the House of the CIBA Foundation. London: Methuen.

Harlow, Harry ( 1966 ). Social Deprivation in Monkeys. Haimowitz, Morris L., editor. In Human Development Selected Readings . New York, Crowell.

Horst, Frank; Veer, René ( 2008 ). Loneliness in Infancy: Harry Harlow, John Bowlby and Issues of Separation. Integrative Psychological and Behavioral Science, 42(4), 325-335. DOI: 10.1007/s12124-008-9071-x

Horst, Frank; LeRoy, Helen; Veer, René ( 2008 ). “When Strangers Meet”: John Bowlby and Harry Harlow on Attachment Behavior. Integrative Psychological and Behavioral Science, 42(4), 370-388. DOI: 10.1007/s12124-008-9079-2

Karr-Morse, Robin; Wiley, Meredith S. ( 2014 ). Ghosts from the Nursery: Tracing the Roots of Violence. Atlantic Monthly Press; 1st edition.

Maté, Gabor ( 2008 ). When the Body Says No. ‎Trade Paper Press; 1st edition.

van Rosmalen, Lenny; van der Veer, René; van der Horst, Frank ( 2020 ). The nature of love: Harlow, Bowlby and Bettelheim on affectionless mothers: . History of Psychiatry, 31(2), 227-231. DOI: 10.1177/0957154×19898997

Vicedo, Marga ( 2010 ). The evolution of Harry Harlow: from the nature to the nurture of love. History of Psychiatry, 21(2), 190-205. DOI: 10.1177/0957154X10370909

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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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Close social bonds are integral for good health and longevity in humans and non-human primates (NHPs), yet we have very little understanding of the neurobiological differences between healthy and unhealthy relationships. Our current understanding of social bonding is grounded in Bowlby’s theory of attachment. Work done with human infants and adult couples has suggested that attachment behavior developed in infancy remains stable through development into adulthood. Unfortunately, knowledge of the neurobiological correlates of attachment behavior has been limited due to a lack of animal models with both infant and adult attachments similar to humans. To address this, we measured behavioral responses to separation from their primary attachment figure in infant and adult titi monkeys (Plecturocebus cupreus). In Experiment 1, we tested for a linear relationship between the subject’s response to separation as an infant and their response to separation as an adult. We found greater decreases in infant locomotor behavior in the presence, as opposed to absence, of their primary attachment figure to be indicative of decreased anxiety-like behavior in the presence, as opposed to absence, of their adult pair mates during a novelty response task. In Experiment 2, we increased our sample size, accounted for adverse early experience, and tested a different outcome measure, adult affiliative behavior. We hypothesized that the level of intensity of an infant’s response to separation would explain affiliative behavior with their mate as an adult, but adverse early experience could change this relationship. When we compared infant response to separation to adult affiliative behavior during the first 6 months of their first adult pair bond, we observed a linear relationship for infants with typical early experience, but not for infants with adverse early experience. Infants with a greater change in locomotive behavior between the father and alone conditions were more affiliative with their first adult pair mate. These data support the use of titi monkeys as an appropriate animal model for further investigation of the neurobiology underlying attachment behavior.

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The Attachment Theory is an approach that argues that the confidence inspired by the mother or by a mother substitute in an individual while still a baby leaves an emotional impact on the development of her offspring. The attachment theory, supported by studies on humans and animals, investigates the feelings of closeness and trust one living thing has for another. Many experiments made in this respect show that some feelings of humans and animals and their offspring are similar in terms of motivations and incentives. The most important of these are concepts such as childcare, abandonment anxiety and bonds of trust and security. In this study, several different scientific studies conducted on animals in terms of the Attachment Theory have been critically reviewed. Moreover, also included in this study is research on the mother-child relationship as compared with studies conducted on animals and their offspring. In the comparisons and evaluations carried out, the psychological effects of bonding, like those in humans, were also observed in animals.

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The clearest way to demonstrate the importance of certain sensory or social stimuli for the normal development of children would be to deprive them of such stimuli and observe the resulting deficits. Obviously, such experiments would be ethically unthinkable. But cases of such deprivation do occasionally arise accidentally, when children are abandoned and grow up alone in nature. Some of these cases have become famous, such as that of the boy Victor, who was discovered in a forest in France in the year 1800 and whose story was the basis of the film by François Truffaut. Despite all the efforts of the people who take them in, such children often remain mute; they cannot learn how to speak or how to behave in a socially acceptable way. The studies that René Spitz conducted in the 1940s were the first to show more systematically that social interactions with other humans are essential for children’s development. Spitz followed two groups of children from the time they were born until they were several years old. The first group were raised in an orphanage, where the babies were more or less cut off from human contact in their cribs, or where a single nurse had to care for seven children. The second group of babies were raised in a nursery in a prison where their mothers were incarcerated. The mothers were allowed to give their babies care and affection every day, and the babies were able to see one another and the prison staff throughout the day. At age 4 months, the state of development of the two groups of babies was similar; the babies in the orphanage even scored a higher average on certain tests. But by the time the babies were 1 year old, the motor and intellectual performance of those reared in the orphanage lagged badly behind those reared in the prison nursery. The orphanage babies were also less curious, less playful, and more subject to infections. During their second and third years of life, the children being raised by their mothers in prison walked and talked confidently and showed development comparable to that of children raised in normal family settings. But of the 26 children reared in the orphanage, only 2 could walk and manage a few words. Since the time of Spitz’s pioneering study, many other experiments have shown what catastrophic effects sensory and social deprivation at certain critical periods in early childhood can have on children’s subsequent development. In the 1960s, Harry Harlow developed an experimental model that took Spitz’s studies even further. In a series of experiments that might be considered cruel today, Harlow took monkeys just a few hours after birth and raised them for 3, 6, or even 12 months in complete isolation from any other monkeys, including their mothers. At the end of the isolation period, when put back with other monkeys, the monkeys who had been isolated remained physically healthy, but their social behaviour was completely disturbed. They would huddle in the corners of their cages and rock back and forth the way some autistic children do; they did not interact with other monkeys, or play, or show any sex drive. But when other monkeys were isolated for periods of comparable length later in life, it had practically no effect on their behaviour. Harlow thus showed beyond any doubt that in monkeys as in humans, there is a critical period for social development. Harlow subsequently conducted other experiments which showed that the social behavioural disorders induced by the period of isolation could be partially reversed if the baby monkeys were given artificial mothers made of wood covered with cloth. The babies would cling to their fake mothers as if they were real, but did not develop any other social skills. But they did develop such skills if, in addition to being given an artificial mother, they were placed in contact for a few hours each day with another young monkey that was growing up normally in a monkey colony.

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Harlow’s Experiment on Rhesus Monkeys

Harry Frederick Harlow is known as one of the best psychoanalysts and behavioral scientists in America. His reputation peaked between the 1950s and the 1960s. As controversial as his experiments were, psychologists and behavioral scientists still consider Harlow’s work revolutionary.

Harlow’s Controversial Experiments

Harlow’s original experiments revolved around his interest in early infancy development, specifically dependence, maternal separation, and social isolation. According to him, the early development of an individual shapes most of their social behaviors. He was determined to turn his theories into facts.

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Superstitions That Have Persisted Throughout the Centuries

The similarity between humans and primates inspired him to use rhesus monkeys to conduct his experiments. With the help of rhesus monkeys, he would prove that babies have often attached to the caregivers that gave them food for more than just food. Harlow and other social and psychotherapists insisted that feeding’s contact comfort played a more significant role in a child’s healthy development.

As popularly reported, Harlow’s experiments took place in an enclosed laboratory at the University of Wisconsin-Madison. The lab afforded the scientist access to plenty of resources, and his controversial work took flight.

Isolation and Deprivation

Harlow’s first experiment involved isolating and depriving infant monkeys of their mothers and raising them in a lab. The infant rhesus monkeys who were completely isolated from other monkeys showed disturbing behavior. When scientists brought them back to a group of monkeys, they were anti-social and self-sabotaging.

The monkeys continued to isolate themselves to the point of starvation and death. Such results came as a surprise because the monkeys were not entirely isolated at this point. Though in different cages, Harlow kept and fed the rhesus monkeys in the same room.

Compared to the control group, all the infant monkeys denied maternal care presented social awkwardness. They were aloof, and they would cling to their soft cloth diapers. Harlow concluded that their need for comfort and maternal care was the cause of this behavior.

The Surrogate Mother

To further his agendas, Harlow introduced the surrogate mother experiment. The two surrogates used in the experiment were objects. One object was wooden with additional strings of wire, while the other one was soft and made out of cloth and rubber.

In one instance, the mother made out of wire and wood would provide the food. Alternatively, the one made out of soft cloth would also take a turn giving the monkeys food. Harlow observed that the surrogate made out of soft material enticed the infant monkeys. With or without the food, the comfy-clothed surrogate provided comfort.

Harlow’s phenomenal and groundbreaking study proved that maternal care, touch, and comfort are essential tools in infant development. Moreover, the study conducted demonstrated that the infant monkeys were more confident in the presence of a caring maternal figure.

Harlow’s theory demonstrates how a maternal figure influences a child’s self-esteem and responsiveness. Seventy years later, Harlow’s experiment still holds precedent in many psychological studies.

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Pit of Despair Isolation Experiment: Why Is It Considered One of the Most Unethical Studies of Modern Science?

In the late-1960s, a scientist designed a scientific apparatus to understand the nature of depression and loneliness.

Pit of Despair Explained

The isolation experiment   was conducted by American psychologists Harry F. Harlow and Stephen J. Suomi to produce an animal model of depression. They wanted to better understand the condition with the hope of finding possible treatments.

In this study, rhesus macaque monkeys were placed into a huge vertical cone-shaped, hard, cold stainless steel structure. The floor was made from wire mesh, allowing poop to drop from the bottom. Inside this pit, the monkeys were fed and given drinking water but left alone for weeks.

The device was named " pit of despair "  by Harlow. The idea behind this setup was to reflect the emotional feelings experienced by humans with severe depression. According to Harlow, depressed humans feel like being sunk into a well of loneliness and hopelessness. From this description, they built an instrument that met the criteria of the pit.

While inside the vertical chamber, most monkeys fell into a still and crowded state within days. These monkeys could not return to normal social behavior when removed from the device. Harlow further described that the animals subjected to the pit of despair for 30 days would not play, avoided social interaction, and showed no sign of curiosity. The majority of the monkeys under study remained still in a huddle position while clasping their bodies with their hands. The profound anomalies in the monkeys' behaviors remained months after being fed from the device.

Although Harlow argued that the device held potential in studying the nature of depression, it is still unclear whether this area of research provided any real insights into clinical depression or any possible approaches to overcome it.

READ ALSO: Animal Testing No Longer an FDA Requirement For New Drugs; Will This Threaten Medical Safety?

Ethics of Animal Testing

Throughout biomedical research, animals have been repeatedly and extensively used. Even during the times of early Greek physicians such as Aristotle and Galen, experiments were performed on living animals.

Over recent years, animal protection and animal rights groups have criticized using animals for research . Since the 17 th  century, there have been debates on the ethical issues of animal testing. As a result, legislation has been passed in various countries to make the practice more humane.

Those who are against animal testing argue that the benefit to humans of such studies does not justify the harm imposed on animals. They believe that animals are inferior to humans and are very different from us, so the results from animal testing cannot be applied to us. On the other hand, those who favor animal testing contend that experiments on animals are essential for advancing medical and biological knowledge.

Since the issues of animal cruelty and humane treatments are valid concerns, the use of animals in research studies has been greatly regulated. Advocates of animal rights promote the 3Rs campaign, which includes the search for replacement of animals with non-living models, reduction in the use of animal samples, and the refinement of animal testing practices.

In 2018, the National Committee for Research Ethics in Science and Technology (NENT) released the Ethical Guidelines for the Use of Animals in Research. It aims to provide ethical guidelines for researchers and other individuals who want to perform animal experiments.

RELATED ARTICLE: Questionable Monkey Research Reignites Animal Testing Arguments

Check out more news and information on Animal Testing  in Science Times.

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NASA’s Juno Probe Captures Lava Lakes Covering Whole Surface of Jupiter’s Moon Io

Graphene Found in China’s Chang’e-5 Lunar Rock Samples; What Does It Say About Early Geological Evolution of the Moon?