Harry Harlow's Monkeys Chose a Cloth-Covered Mother Who Couldn't Feed Them

When Harry Harlow stood up at the American Psychological Association's annual meeting on August 31, 1958, the prevailing theory of mother-infant attachment in mainstream behaviorism was that babies bonded with whoever fed them. Drive-reduction theory; the milk was the reward; the rest followed. Harlow's lecture, titled "The Nature of Love," was a calculated hand grenade thrown at this idea. He showed films of baby rhesus monkeys at the University of Wisconsin presented with two surrogate mothers: one a wire mesh frame with a baby bottle protruding from the chest, the other an identically shaped frame covered in soft terrycloth, with no food. The monkeys clung to the cloth mother nearly all the time, leaving her only briefly to drink from the wire mother before scrambling back. When startled by a loud, mechanical "monster" toy, the babies ran to the cloth mother, not the one with the food.

The interpretation was that contact comfort — soft, warm physical contact — was a primary need on its own, not derivative of feeding. The result lined up with John Bowlby's work on human attachment in orphanages and helped move developmental psychology away from drive theory toward attachment theory.

Harlow's later experiments are harder to read. Through the 1960s and into the early 1970s he ran isolation studies that confined infant monkeys alone, sometimes in stainless-steel chambers he himself called the "Pit of Despair," for periods up to twelve months. The animals emerged severely psychologically damaged. The protocols are now textbook examples of unethical research and contributed directly to the U.S. Animal Welfare Act of 1966. The wire-and-cloth experiment, conducted in something closer to ordinary cages, remains widely cited; the isolation work is a different kind of citation.