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Harry Harlow
Born October 31, 1905(1905-10-31)
 Fairfield, Iowa, U.S.
Died December 6, 1981 (aged 76)
Nationality United States
Fields Psychology
Notable awards National Medal of Science (1967)
Gold Medal from American Psychological
Foundation (1973)
Howard Crosby Warren Medal (1956)

Harry Frederick Harlow (October 31, 1905 ‚Äď December 6, 1981) was an American psychologist best known for his maternal-separation and social isolation experiments on rhesus monkeys, which demonstrated the importance of care-giving and companionship in social and cognitive development. He conducted most of his research at the University of Wisconsin‚ÄďMadison, where humanistic psychologist Abraham Maslow worked for a time with him.

Harlow's experiments were controversial; they included rearing infant macaques in isolation chambers for up to 24 months, from which they emerged severely disturbed.[1] Some researchers cited the experiments as a factor in the rise of the animal liberation movement in the United States.



Born Harry Israel on October 31, 1905 to Mabel Rock and Alonzo Harlow Israel, Harlow grew up in Fairfield, Iowa, the second youngest of four brothers. After a year at Reed College in Portland, Oregon, Harlow obtained admission to Stanford University on a special aptitude test. After a semester as an English major with nearly disastrous grades, he declared himself as a psychology major.

Harlow studied largely under Lewis Terman, the developer of the Stanford-Binet IQ Test, who helped shaped Harlow's future. After receiving a Ph.D. in 1930, Harlow changed his name from Israel to Harlow.

Directly after completing his doctoral dissertation, Harlow accepted a professorship at the University of Wisconsin‚ÄďMadison. In terms of departmental development, his most significant achievement was his persuasion of the University to construct the Primate Laboratory, one of the first of its kind in the world. Under Harlow's direction, it became a place of cutting-edge research at which some 40 students earned their Ph.D.s.

Harlow received numerous awards and honors, including the Howard Crosby Warren Medal (1956), the National Medal of Science (1967), and the Gold Medal from the American Psychological Foundation (1973). He served as head of the Human Resources Research branch of the Department of the Army from 1950-1952, head of the Division of Anthropology and Psychology of the National Research Council from 1952-1955, consultant to the Army Scientific Advisory Panel, and president of the American Psychological Association from 1958-1959.

Harlow's personal life was complicated, and at times, alienated from his mother. He first married Clara Mears in 1932. One of the select children with an IQ above 150 whom Terman studied at Stanford, Clara was Harlow's student before becoming romantically involved with him. The couple had two children, Robert and Richard. Harlow and Mears divorced in 1946. That same year, Harlow married child psychologist Margaret Kuenne. The marriage produced another two children, Pamela and Jonathan. Margaret died in 1970 after a prolonged struggle with cancer. In 1971, Harlow remarried Clara Mears. The couple lived together in Tucson, Arizona until Harlow's death in 1981.

Surrogate mother experiment

In a well-known series of experiments conducted between 1957 and 1963, 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.

The studies were motivated by John Bowlby's World Health Organization-sponsored study and report, "Maternal Care and Mental Health" in 1950, in which Bowlby reviewed previous studies on the effects of institutionalization on child development such as René Spitz's[2] and his own surveys on children raised in a variety of settings. In 1953, his colleague, James Robertson, produced a short and controversial documentary film titled A Two-Year-Old Goes to Hospital demonstrating the almost immediate effects of maternal separation. Bowlby's report, coupled with Robertson's film, demonstrated the importance of the primary caregiver in human and non-human primate development. Bowlby de-emphasized the mother's role in feeding as a basis for the development of a strong mother-child relationship. However, his conclusions generated much debate. It was this debate about the reasons behind the demonstrated and acknowledged need for maternal care, that was addressed by Harlow in his studies with the cloth and wire surrogates.

In Harlow's classic experiment, two groups of baby rhesus monkeys were removed from their mothers. In the first group, a terrycloth mother provided no food, while a wire mother did, in the form of an attached baby bottle containing milk. In the second group, a terrycloth mother provided food; the wire mother did not. It was found that the young monkeys clung to the terrycloth mother whether or not it provided them with food, 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. This response decreased as the monkeys grew older.

When the monkeys were placed in an unfamiliar room with their cloth surrogate, they clung to it until they felt secure enough to explore. Once they began to explore, they occasionally returned to the cloth mother for comfort. Monkeys placed in an unfamiliar room without their cloth mothers acted very differently. They froze in fear and cried, crouched down, or sucked their thumbs. Some even ran 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 concluded 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's interpretation of this behavior, which is still widely accepted, was that lack of contact comfort was psychologically stressful to the monkeys.

The importance of these findings is that they contradicted both the then common pedagogic advice of limiting or avoiding bodily contact in an attempt to avoid spoiling children and the insistence of the then dominant behaviorist school of psychology that emotions were negligible. Feeding was thought to be the most important factor in the formation of a mother-child bond. Harlow concluded, however, that nursing strengthened the mother-child bond because of the intimate body contact that it provided. He described his experiments as a study of love. He also believed that contact comfort could be provided by either mother or father. Though widely accepted now, this idea was revolutionary at the time.[citation needed]

Critics of Harlow's research 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, overestimate the importance of contact comfort and underestimate the importance of nursing.[3]

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, D.C., August 31, 1958.

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 et al. reported that partial isolation resulted in various abnormalities such as blank staring, stereotyped repetitive circling in their cages, and self-mutilation. These monkeys were then observed in various settings. Some of the monkeys remained in solitary confinement for 15 years.[4]

In the total isolation experiments baby monkeys would be left alone for three, six, 12, or 24[5][6] months of "total social deprivation." The experiments produced monkeys that were severely psychologically disturbed. Harlow wrote:

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 ...[1]

Harlow tried to reintegrate the monkeys who had been isolated for six months by placing them with monkeys who had been reared normally.[7][8] 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."[9] Isolates exposed to monkeys the same age who were reared normally "achieved only limited recovery of simple social responses."[9] 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."[9] Isolates given to surrogate mothers developed "crude interactive patterns among themselves."[9] 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."[10] 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.[11]

Since Harlow's pioneering work in touch research in development, recent work in rats have found evidence that touch during infancy have resulted in a decrease in corticosteroid, a steroid hormone involved in stress, and an increase in glucocorticoid receptors in many regions of the brain [12]. Schanberg and Field found that even short-term interruption of mother-pup interaction in rats markedly affected several biochemical processes in the developing pup: a reduction in ornithine decarboxylase (ODC) activity, a sensitive index of cell growth and differentiation; a reduction in growth hormone release (in all body organs, including the heart and liver and throughout the brain, including the cerebrum, cerebellum and brain stem); an increase in corticosterone secretion; and suppressed tissue ODC responsivity to administered growth hormone [13]. Additionally, it has been found that these animals who were touch deprived had weakened immune systems. Investigators have measured a direct, positive relationship between the amount of contact and grooming an infant monkey receives during its first six months of life and its ability to produce antibody titer (IgG and 1gM) in response to an antibody challenge (tetanus) at a little over one year of age [14]. Trying to identify a mechanism for the "immunology of touch," some investigators point to modulations of arousal and associated CNS-hormonal activity. Touch deprivation may cause stress-induced activation of the pituitary-adrenal system, which, in turn, leads to increased plasma cortisol and adrenocorticotropic hormone. Likewise, researchers suggest, regular and "natural" stimulation of the skin may moderate these pituitary-adrenal responses in a positive and healthful way [15].


Pit of despair

Harlow was well known for refusing to use conventional terminology, and instead chose deliberately outrageous terms for the experimental apparatus he devised. The tendency arose from an early conflict with the conventional psychological establishment in which Harlow used the term "love" in place of the popular and archaically correct term, "attachment." Such terms and respective devices included a forced-mating device he called the "rape rack," tormenting surrogate mother devices he called "Iron maidens," and an isolation chamber he called the "pit of despair" developed by him and a graduate student, Stephen Suomi, now 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.[16]

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." (p. 458)[17]


Harlow's research, though controversial, has provided insight into the behaviors of abused children and has improved methods of providing care to institutionalized children. While many of his experiments would be considered unethical today, their nature and Harlow's descriptions of them heightened awareness of the treatment of laboratory animals and thus paradoxically contributed somewhat to today's ethics regulations.[citation needed]

Critics, such as Deborah Blum, have called the results of his research "common sense results": that monkeys, very social animals in nature, when placed in isolation emerge badly damaged, and that some recover and some do not.[18]

Gene Sackett of the University of Washington in Seattle, who was one of Harlow's doctoral students, has stated that he believes the animal liberation movement in the U.S. was born as a result of Harlow's experiments.[18]

Willam Mason, another of Harlow's students who continued deprivation experiments after leaving Wisconsin,[19] has said 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."[20]


Year Event
1905 Born October 31 in Fairfield, Iowa Son of Alonzo and Mabel (Rock) Israel
1930-44 Staff, University of Wisconsin‚ÄďMadison
Married Clara Mears
1939-40 Carnegie Fellow of Anthropology at Columbia University
1944-74 George Cary Comstock Research Professor of Psychology
1946 Divorced Clara Mears
Married Margaret Kuenne
1947-48 President, Midwestern Psychological Association
1950-51 President of Division of Experimental Psychology, American Psychological Association
1950-52 Head of Human Resources Research Branch, Department of the Army
1953-55 Head of Division of Anthropology and Psychology, National Research Council
1956 Howard Crosby Warren Medal for outstanding contributions to the field of experimental psychology
1956-74 Director of Primate Lab, University of Wisconsin
1958-59 President, American Psychological Association
1959,65 Sigma Xi National Lecturer
1960 Distinguished Psychologist Award, American Psychological Association
Messenger Lecturer at Cornell University
1961-71 Director of Regional Primate Research Center
1964-65 President of Division of Comparative & Physiological Psychology, American Psychological Association
1967 National Medal of Science
1970 Death of his spouse, Margaret
1971 Harris Lecturer at Northwestern University
Remarried Clara Mears
1972 Martin Rehfuss Lecturer at Jefferson Medical College
Gold Medal from American Psychological Foundation
Annual Award from Society for the Scientific Study of Sexuality
1974 University of Arizona (Tucson) Honorary Research Professor of Psychology
1975 Von Gieson Award from New York State Psychiatric Institute
1976 International Award from Kittay Scientific Foundation
1981 Died December 6, 1981

Early papers

  • The effect of large cortical lesions on learned behavior in monkeys. Science. 1950.
  • Retention of delayed responses and proficiency in oddity problems by monkeys with preoccipital ablations. Am J Psychol. 1951.
  • Discrimination learning by normal and brain operated monkeys. J Genet Psychol. 1952.
  • Incentive size, food deprivation, and food preference. J Comp Physiol Psychol. 1953.
  • Effect of cortical implantation of radioactive cobalt on learned behavior of rhesus monkeys. J Comp Physiol Psychol. 1955.
  • The effects of repeated doses of total-body x radiation on motivation and learning in rhesus monkeys. J Comp Physiol Psychol. 1956.


  1. ^ a b Harlow HF, Dodsworth RO, Harlow MK. "Total social isolation in monkeys," Proc Natl Acad Sci U S A. 1965.
  2. ^ Spitz, R. A., & Wolf, K. M. Anaclitic depression: an inquiry into the genesis of psychiatric conditions in early childhood. II. Psychoanalytic Study of the Child,(2),313-342. 1946.
  3. ^ Mason, W.A. Early social deprivation in the nonhuman primates: Implications for human behavior. 70-101; in D.C. Glass (ed.) Environmental Influences. New York: Rockefeller University and Russell Sage Foundation, 1968.
  4. ^ A variation of this housing method, using cages with solid sides as opposed to wire mesh, but retaining the one-cage, one-monkey scheme, remains a common housing practice in primate laboratories today. (Reinhardt V, Liss C, Stevens C. "Social Housing of Previously Single-Caged Macaques: What are the options and the Risks?" Universities Federation for Animal Welfare, Animal Welfare 4: 307-328. 1995.)
  5. ^ Harlow, H.F. Development of affection in primates. Pp. 157-166 in: Roots of Behavior (E.L. Bliss, ed.). New York: Harper. 1962.
  6. ^ Harlow, H.F. Early social deprivation and later behavior in the monkey. Pp. 154-173 in: Unfinished tasks in the behavioral sciences (A.Abrams, H.H. Gurner & J.E.P. Tomal, eds.) Baltimore: Williams & Wilkins. 1964.
  7. ^ Suomi, S. J., Leroy, H. A. "In memoriam: Harry F. Harlow (1902-1981). Amer. J. Prim. 2: 319-342.
  8. ^ 1976 Suomi SJ, Delizio R, Harlow HF. "Social rehabilitation of separation-induced depressive disorders in monkeys."
  9. ^ a b c d Harlow, Harry F. and Suomi, Stephen J. (1971). "Social Recovery by Isolation-Reared Monkeys", Proceedings of the National Academy of Science of the United States of America 68(7):1534-1538.
  10. ^ Harlow, Harry F. and Suomi, Stephen J. (1971). "Social Recovery by Isolation-Reared Monkeys", Proceedings of the National Academy of Science of the United States of America 68(7):1534-1538; Suomi, Stephen J; Harlow, Harry F; McKinney, William T. (1972) "Monkey Psychiatrists", American Journal of Psychiatry 128:927-932.
  11. ^ Cummins, Mark S. and Suomi, Stephen J. (1976) "Long-term effects of social rehabilitation in rhesus monkeys", Primates 17(1):43-51.
  12. ^
  13. ^ Schanberg S, and Field T. Maternal deprivation and supplemental stimulation. In Stress and Coping Across Development, Field T, McCabe P, and Schneiderman N, eds. Hillsdale, NJ: Erlbaum; 1988.
  14. ^ Laudenslager ML, Rasmussen KLR, Berman CM, Suomi SJ, and Berger CB. Specific antibody levels in free-ranging rhesus monkeys: relationships to plasma hormones, cardiac parameters, and early behavior. Developmental Psychology. 1993;26:407-420.
  15. ^ Suomi SJ. Touch and the immune system in rhesus monkeys. In Touch in Early Development, Field TM, ed. Hillsdale, NJ: Lawrence Erlbaum Assoc.; (in press).
  16. ^ Suomi, JS. "Experimental production of depressive behavior in young monkeys." Doctoral thesis. University of Wisconsin‚ÄďMadison, 1971.
  17. ^ Harlow, H.F., Harlow, M.K., Suomi, S.J. From thought to therapy: lessons from a primate laboratory. 538-549; Americam Scientist. vol. 59. no. 5. September-October; 1971.
  18. ^ a b Blum, Deborah. Love at Goon Park: Harry Harlow and the Science of Affection. Perseus Publishing, 2002, p. 225.
  19. ^ Capitanio, J.P. & Mason, W.A. "Cognitive style: problem solving by rhesus macaques (Macaca mulatta) reared with living or inanimate substitute mothers", California Regional Primate Research Center, University of California, Davis. 1: J Comp Psychol. 2000 Jun;114(2):115-25.
  20. ^ Blum, Deborah. The Monkey Wars. Oxford University Press, 1994, p. 96.

Further reading


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