Harry Frederick Harlow (October 31, 1905–December 6, 1981) was an American psychologist best known for his maternal-deprivation and social isolation experiments on rhesus monkeys. A graduate of Stanford University, Harlow conducted his research at the University of Wisconsin-Madison. His work demonstrated the importance of care-giving and companionship in the early stages of primate development, and by extension for human beings.
Controversial to the extent of being infamous, Harlow conducted numerous experiments to investigate the nature of love. Starting as a study of factors involved in mother-infant bonding, Harlow's research soon entered areas that were questionable at best, and often unethical. In his attempts to understand mothering, Harlow raised monkeys with artificial mothers that ranged from inadequate to abusive. The results, "motherless mothers," were as incompetent in mothering their own infants as were the wire and cloth surrogates Harlow had built.
Harlow never expressed any regret at the damage he inflicted on his monkeys, regarding his research as having the potential to save millions of children from abuse. Indeed, his efforts to understand the nature of love informed scientists that touch, comfort, and social interaction were essentials of healthy psychological development. While the brutality of his experiments is shocking, Harlow's motivation was deeper understanding of human nature. He sought to discover the secrets of love through his science, and in his darker years he sought to understand what caused depression and mental disorders, and when he succeeded in making his monkeys depressed, even psychotic, he sought to cure them, but to no avail.
Born Harry Israel on October 31, 1905 to Lon and Mabel Israel, he changed his name to Harry Harlow in 1930. Harry grew up in Iowa in a small farming community. The family was poor as his father was more interested in coming up with inventions than in succeeding in business. Harry grew up shy, awkward, and insecure, but always ready to laugh at himself: "I tended to apologize to doors before opening them." And he always dreamed big.
He earned his Ph.D. in psychology from Stanford University in 1930, where he worked with Lewis Terman, the IQ test researcher who was studying gifted children. It was Terman who suggested that, due to the extreme anti-Semitism of the time, Harry should change his Jewish sounding name. He took the advice and adopted his father's middle name, becoming Harry Harlow.
He married Clara Mears, one of Terman's gifted children, to Terman's delight, regarding her intelligence and Harlow's research abilities as an excellent match. They had two sons, but Clara soon left him taking the children with her, saying Harry had basically abandoned them for his work anyway. Harlow had taken a job at the University of Wisconsin in Madison, immediately upon graduating and established a primate laboratory where he spent his whole career. His second wife was a colleague in child psychology, Peggy Kuenne. They also had two children, but he spent little time at home, always immersed in his research. When she died of cancer in 1971, though, Harlow was devastated, retiring a year later to Arizona.
Harlow's motivation for his research was to understand love. Theories of love at that time focused on physical aspects of life, explaining love in terms of the satisfaction of needs and drives, such as hunger and thirst. The maternal bond between mother and child was thought to begin through feeding. Beginning in 1957, Harlow began to investigate the nature of this bond. While his experiments appear cruel, and even he admitted his monkeys suffered, the suffering was caused more by ignorance and Harlow's desire to learn about love than any unethical treatment, at least in the initial studies.
Essentially, Harlow took infant monkeys from their mothers at birth, substituting a variety of artificial "mothers" as surrogates. Harlow built several styles of "mother," some of wire, some of cloth, some with milk, some with faces, and so forth. Based on his experiments, he designed what he thought was the ideal mother, a soft mother covered in terry cloth that the infant monkeys could cling to: "a mother, soft, warm, and tender, a mother with infinite patience, a mother available 24 hours a day."
Harlow first reported the results of these experiments in "The nature of love," the title of his address to the sixty-sixth Annual Convention of the American Psychological Association, Washington, DC, August 31, 1958. He illustrated his speech with powerful film clips of the artificial surrogate mothers and the infant monkeys who depended on them, and spoke at the end of the "practical applications" of his research.
In the climate of the time, when researchers talked not about love but "proximity," and psychologists such as John Watson had warned that parents who cuddled and kissed their children were training them to be weak and clingy, Harlow's presentation was revolutionary. His work showed that the mother-child relationship was built on touch, not on feeding, and was a relationship of love not training. This revived John Bowlby's theory of attachment and was the foundation for the whole science of touch that has emerged. For this phase of his research, Harlow received the National Medal of Science in 1967.
However, Harlow's monkeys did not thrive on cloth mothers alone. He soon found that his ideal mother was a social failure—her children were unable to relate to other monkeys. Pursuing this line of research, Harlow's experiments soon became darker, studying the effects of social isolation, and the final ones on the "pit of despair" haunted his research associates for years.
At this time Harlow's personal life had also become dark. In 1967, his wife, Peggy, was diagnosed with cancer, dying in 1971. During her illness Harlow became severely depressed, and after her death he submitted to Electroconvulsive therapy. Harlow was never the same. He continued his research briefly, but failed to find any cure for the psychosis he had caused in the monkeys who were isolated for long periods. They were too damaged to be reached; with no way to bring them back.
He retired in 1973, leaving Madison, and his former colleagues dismantled the isolation chambers immediately. Harlow died on December 6, 1981 of Parkinson's disease.
Harlow joined the faculty at the University of Wisconsin in Madison immediately after obtaining his Ph.D. from Stanford University. Within a year, he had established a primate laboratory, which expanded until it merged with the Wisconsin Regional Primate Lab in 1964, of which Harlow became the director. Abraham Maslow, who later established Humanistic psychology, was one of the many scientists to work there. His early studies focused on primate intelligence, studying learning and memory, and their ability to form "learning sets" or "learn to learn."
Harlow's lab produced ground-breaking research in the mid-twentieth century. His studies of maternal deprivation revealed information about the essence of motherhood, albeit in shocking ways. Some of Harlow's experiments involved rearing infant macaques in isolation chambers that prevented them from having any contact with other monkeys or human beings. The monkeys were left alone for up to 24 months, and emerged severely disturbed. As a result, Harlow's work is considered unethical today.
Surrogate mother experiment
In a well-known series of experiments conducted between 1963 and 1968, Harlow removed baby rhesus monkeys from their mothers, and offered them a choice between two surrogate "mothers," one made of terrycloth, the other of wire.
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. In the second group, the terrycloth mother provided food; the wire mother did not. It was found that the young monkeys clung to the terrycloth mother whether it provided them with food or not, and that the young monkeys chose the wire surrogate only when it provided food.
Whenever a frightening stimulus was brought into the cage, the monkeys ran to the cloth mother for protection and comfort, no matter which mother provided them with food. When the monkeys were placed in an unfamiliar room with their cloth surrogates, they clung to them until they felt secure enough to explore. Once they began to explore, they would occasionally return to the cloth mother for comfort. Monkeys placed in an unfamiliar room without their cloth mothers acted very differently. They would freeze in fear and cry, crouch down, or suck their thumbs. Some of the monkeys would even run from object to object, apparently searching for the cloth mother as they cried and screamed. Monkeys placed in this situation with their wire mothers exhibited the same behavior as the monkeys with no mother.
Once the monkeys reached an age where they could eat solid foods, they were separated from their cloth mothers for three days. When they were reunited with their mothers they clung to them and did not venture off to explore as they had in previous situations. Harlow claimed from this that the need for contact comfort was stronger than the need to explore.
The study found that monkeys who were raised with either a wire mother or a cloth mother gained weight at the same rate. However, the monkeys that had only a wire mother had trouble digesting the milk and suffered from diarrhea more frequently. Harlow interpreted this to mean that not having contact comfort was psychologically stressful to the monkeys.
Critics of Harlow's claims have observed that clinging is a matter of survival in young rhesus monkeys, but not in humans, and have suggested that his conclusions, when applied to humans, overestimated the importance of contact comfort and underestimated the importance of nursing. 
Harlow soon realized, though, that touch was not enough, and his "ideal mother" was inadequate. When the monkeys reared with cloth surrogates were finally introduced to other real monkeys, they were violently anti-social. They displayed autistic-like behavior, banging their heads and rocking. They were unable to mate normally, and when Harlow forced females into mating using restraints, which he called the "rape rack," they were negligent or abusive of their children. These "motherless mothers," deprived of emotional bonds from birth, were unable to form any attachment with their own offspring.
Partial and total isolation of infant monkeys
From around 1960 onwards, Harlow and his students began publishing their observations on the effects of partial and total social isolation. Partial isolation involved raising monkeys in bare wire cages that allowed them to see, smell, and hear other monkeys, but provided no opportunity for physical contact. Total social isolation involved rearing monkeys in isolation chambers that precluded any and all contact with other monkeys.
Harlow reported that partial isolation resulted in various abnormalities such as blank staring, stereotyped repetitive circling in their cages, and self-mutilation. In the total isolation experiments baby monkeys would be left alone for three, six, 12, or 24 months of "total social deprivation." The experiments produced monkeys that were severely psychologically disturbed:
No monkey has died during isolation. When initially removed from total social isolation, however, they usually go into a state of emotional shock, characterized by ... autistic self-clutching and rocking. One of six monkeys isolated for 3 months refused to eat after release and died 5 days later. The autopsy report attributed death to emotional anorexia. …. The effects of 6 months of total social isolation were so devastating and debilitating that we had assumed initially that 12 months of isolation would not produce any additional decrement. This assumption proved to be false; 12 months of isolation almost obliterated the animals socially.
Harlow tried to reintegrate the monkeys who had been isolated for six months by placing them with monkeys who had been reared normally. The rehabilitation attempts met with limited success. Harlow wrote that total social isolation for the first six months of life produced "severe deficits in virtually every aspect of social behavior." Isolates exposed to monkeys the same age who were reared normally "achieved only limited recovery of simple social responses." Some monkey mothers reared in isolation exhibited "acceptable maternal behavior when forced to accept infant contact over a period of months, but showed no further recovery." Isolates given to surrogate mothers developed "crude interactive patterns among themselves." Opposed to this, when six-month isolates were exposed to younger, three-month-old monkeys, they achieved "essentially complete social recovery for all situations tested." The findings were confirmed by other researchers, who found no difference between peer-therapy recipients and mother-reared infants, but found that artificial surrogates had very little effect.
Pit of despair
Harlow was well known for refusing to use euphemisms and instead chose deliberately outrageous terms for the experimental apparatus he devised. These included a forced mating device he called a "rape rack," tormenting surrogate mother devices he called "iron maidens," and an isolation chamber he called the "pit of despair" developed by Harlow and his student, Steven Suomi, who became director of the National Institute of Child Health and Human Development's Comparative Ethology Laboratory, at the National Institutes of Health.
In the latter of these devices, alternatively called the "well of despair," baby monkeys were left alone in darkness for up to one year from birth, or repetitively separated from their peers and isolated in the chamber. These procedures quickly produced monkeys that were severely psychologically disturbed and declared to be valuable models of human depression.
Harlow tried to rehabilitate monkeys that had been subjected to varying degrees of isolation using various forms of therapy. "In our study of psychopathology, we began as sadists trying to produce abnormality. Today we are psychiatrists trying to achieve normality and equanimity."
Harlow's experiments were controversial, with some researchers citing them as factors in the rise of the animal liberation movement. William Mason, who worked with Harlow, told writer Deborah Blum that Harlow
kept this going to the point where it was clear to many people that the work was really violating ordinary sensibilities, that anybody with respect for life or people would find this offensive. It's as if he sat down and said, 'I'm only going to be around another ten years. What I'd like to do, then, is leave a great big mess behind.' If that was his aim, he did a perfect job.
Harlow's experiments have been called cruel, even brutal, but the outcome of his work affirmed that human beings live in a world that is more complex than that of simple physical needs, like hunger. His work emphasized that we are essentially social beings, initially seeking the warmth and comfort of touch, that the first face we see is the one we find most beautiful, and that we need time to play and others of our species to play with in order develop psychologically as well as physically.
Harlow did not regret the experiments, even though he acknowledged his monkeys suffered. For Harlow, human beings were more important. He was willing to sacrifice ten monkeys to save a million children from mistreatment. While Harlow's experiments remain as horror stories, the outcome is that we have learned to be more human. Orphanages and caregivers now know that simply propping a bottle for an infant to drink from is not enough; they need to be held, cuddled, rocked, and see a human face smile at them.
It is hard to imagine that his research that showed the significance of touch was so revolutionary. But in his time, many psychologists rejected the word love, talking only of "proximity" between mother and child. Harlow, a man who by all accounts lived a rather isolated life himself, still retorted to such comments, "Perhaps all you've known is proximity. I thank God that I've known more."
- Harlow, Harry F. "The effect of large cortical lesions on learned behavior in monkeys." Science (1950).
- Harlow, Harry F. "Retention of delayed responses and proficiency in oddity problems by monkeys with preoccipital ablations." Am J Psychol (1951).
- Harlow, Harry F. "Discrimination learning by normal and brain operated monkeys." J Genet Psychol (1952).
- Harlow, Harry F. "Incentive size, food deprivation, and food preference." J Comp Physiol Psychol (1953).
- Harlow, Harry F. "Effect of cortical implantation of radioactive cobalt on learned behavior of rhesus monkeys." J Comp Physiol Psychol (1955).
- Harlow, Harry F. "The effects of repeated doses of total-body x radiation on motivation and learning in rhesus monkeys." J Comp Physiol Psychol (1956).
- Harlow, Harry F. The Nature of Love, American Psychologist 13 (1958): 573-685. Retrieved June 8, 2008.
- Harlow, Harry F. Biological and Biochemical Bases of Behavior. University of Wisconsin Press, 1958.
- Harlow, Harry F., et al. "Nature of love: Simplified." American Psychologist 25(2) (1970): 161-168.
- Harlow, Harry F. and Suomi, Stephen J. "Social Recovery by Isolation-Reared Monkeys." Proceedings of the National Academy of Science of the United States of America 68(7) (1971):1534-1538.
- Harlow, H., et al. "The sad ones: Studies in depression." Psychology Today 4(12) (1971): 61-63.
- Harlow, Harry F. "A variable-temperature surrogate mother for studying attachment in infant monkeys." Behavior Research Methods 5(3) (1973): 269-272.
- Harlow, Harry F. "Lust, latency and love: Simian secrets of successful sex." Journal of Sex Research 11(2) (1975): 79-90.
- Harlow, Harry F. Learning to Love. Jason Aronson, 1978. ISBN 978-0876681596
- Harlow, Harry F. Human Model: Primate Perspective. Vh Winston, 1979. ISBN 978-0470266427
- Harlow, Harry F. and Clara Mears Harlow (ed.). From Learning to Love: The Selected Papers of H.F. Harlow. Praeger Publishers, 1986. ISBN 978-0275922245
- Harlow, Harry F. et al. "Effects of maternal and peer separations on young monkeys." Journal of Child Psychology & Psychiatry & Allied Disciplines 17(2) (1976): 101-112.
- Harlow, Harry F. et al. "Social rehabilitation of separation-induced depressive disorders in monkeys." American Journal of Psychiatry. 133(11), (1976): 1279-1285.
- Harlow, Harry F, and Robert Zimmermann. "Affectional responses in the infant monkey." In Lynne D. Houck and Lee C. Drickamer (eds) Foundations of Animal Behavior published in Association with the Animal Behavior Society, 1996, 376-387. ISBN 978-0226354576
- Schrier, Allan Martin, Harry F. Harlow, and Fred Stollnitz. Behavior of Nonhuman Primates: Modern Research Trends. New York, NY: Academic Press, 1965.
- Deborah Blum, The Inventor of the Cloth Mother NZZ Folio (2003). Retrieved June 24, 2008.
- Lauren Slater, Monkey Love, The Boston Globe, March 21, 2004. Retrieved June 8, 2008.
- Harry F. Harlow, "The formation of learning sets," Psychological Review 56 (1949): 51–65
- Harry F. Harlow, R. O. Dodsworth, and M. K. Harlow, "Total social isolation in monkeys," Proc Natl Acad Sci U S A (1965).
- W. A. Mason, "Early social deprivation in the nonhuman primates: Implications for human behavior," D. C. Glass, (ed.) Environmental Influences (New York, NY: Rockefeller University and Russell Sage Foundation, 1968) 70-101.
- Harry F. Harlow, et al., "Effects of maternal and peer separations on young monkeys," Journal of Child Psychology & Psychiatry & Allied Disciplines 17(2) (1976): 101-112.
- Harry F. Harlow, "Development of affection in primates," in Roots of Behavior, E. L. Bliss, (ed.) (New York, NY: Harper, 1962), 157-166.
- Harry F. Harlow, "Early social deprivation and later behavior in the monkey," in Unfinished Tasks in the Behavioral Sciences, A. Abrams, H.H. Gurner & J.E.P. Tomal, (eds.) (Baltimore, MD: Williams & Wilkins, 1964)
- S. J. Suomi and H. A. Leroy, "In memoriam: Harry F. Harlow (1902-1981). Amer. J. Prim 2(1981): 319-342.
- S. J. Suomi, R. Delizio, and Harry F. Harlow, "Social rehabilitation of separation-induced depressive disorders in monkeys," American Journal of Psychiatry 133(11) (1976): 1279-1285
- Harry F. Harlow and Stephen J. Suomi, "Social Recovery by Isolation-Reared Monkeys", Proceedings of the National Academy of Science of the United States of America 68(7) (1971):1534-1538.
- Harry F. Harlow and Stephen J. Suomi, "Social Recovery by Isolation-Reared Monkeys", Proceedings of the National Academy of Science of the United States of America 68(7) (1971):1534-1538; Stephen J. Suomi, Harry F. Harlow, and William T. McKinney, "Monkey Psychiatrists", American Journal of Psychiatry 128 (1972): 927-932.
- Mark S. Cummins and Stephen J. Suomi, "Long-term effects of social rehabilitation in rhesus monkeys", Primates 17(1) (1976):43-51.
- S. J. Suomi, "Experimental production of depressive behavior in young monkeys," Doctoral thesis. University of Wisconsin-Madison, 1971.
- Harry F. Harlow, M.K. Harlow, and S.J. Suomi, "From thought to therapy: lessons from a primate laboratory," American Scientist 59 (5) (September-October 1971): 538-549
- Deborah Blum. The Monkey Wars. (Oxford University Press, 1994), 96.
- Bliss, Eugene L. ed. Roots of Behavior: Genetics, Instinct, and Socialization in Animal Behavior. New York: Macmillan Pub Co, 1969. ISBN 978-0028415406
- Blum, Deborah. The Monkey Wars. Oxford University Press, 1994. ISBN 019510109X
- Blum, Deborah. Love at Goon Park: Harry Harlow and the Science of Affection. Perseus Publishing, 2002. ISBN 0738202789
- Blum, Deborah. The Inventor of the Cloth Mother NZZ Folio (2003) Retrieved June 24, 2008.
- Cummins, Mark S. and Stephen J. Suomi, "Long-term effects of social rehabilitation in rhesus monkeys," Primates 17(1) (1976):43-51.
- Harlow, Harry F., R. O. Dodsworth, and M. K. Harlow, "Total social isolation in monkeys," Proc Natl Acad Sci U S A 1965.
- Harlow, Harry F., M.K. Harlow, and S.J. Suomi, "From thought to therapy: lessons from a primate laboratory," American Scientist 59 (5) (September-October 1971): 538-549.
- Harlow, Harry F. and Stephen J. Suomi, "Social Recovery by Isolation-Reared Monkeys," Proceedings of the National Academy of Science of the United States of America 68(7) (1971): 1534-1538.
- Mason, W. A. "Early social deprivation in the nonhuman primates: Implications for human behavior," in D. C. Glass, (ed.) Environmental Influences. New York, NY: Rockefeller University and Russell Sage Foundation, 1968, 70-101.
- Reinhardt, V., C. Liss, and C. Stevens, Social Housing of Previously Single-caged Macaques: What are the Options and the Risks?, Animal Welfare 4(4) (1995): 307-328. Retrieved June 25, 2008.
- Slater, Lauren. Monkey Love, The Boston Globe, March 21, 2004. Retrieved June 8, 2008.
- Slater, Lauren. Opening Skinner's Box: Great Psychological Experiments of the Twentieth Century. New York: W.W. Norton & Company, 2004. ISBN 0393050955
- Suomi, Stephen J. "Experimental production of depressive behavior in young monkeys." Doctoral thesis. University of Wisconsin-Madison, 1971.
All links retrieved August 3, 2017.
- Harry Harlow: Monkey Love Experiments - Adoption History
- Harry Harlow - A Science Odyssey: People and Experiments
- Harlow et al. "Total social isolation in monkeys." Proc Natl Acad Sci U S A. 1965 July; 54(1): 90–97.
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