Harry Frederick Harlow (October 31, 1905 – 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–Madison, where humanistic psychologistAbraham 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. Some researchers cite the experiments as a factor in the rise of the animal liberation movement in the United States.
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 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 the debate concerning the reasons behind the demonstrated need for maternal care that Harlow addressed in his studies with surrogates.