Harry Harlow was one of the first psychologists to scientifically investigate the nature of human love and affection. Through a series of controversial experiments, Harlow was able to demonstrate the importance of early attachments, affection, and emotional bonds on the course of healthy development.﻿﻿

A History of Research on Love and Affection

During the first half of the 20th century, many psychologists believed that showing affection towards children was merely a sentimental gesture that served no real purpose. Behaviorist John B. Watson once even went so far as to warn parents, "When you are tempted to pet your child, remember that mother love is a dangerous instrument."

According to many thinkers of the day, affection would only spread diseases and lead to adult psychological problems.

During this time, psychologists were motivated to prove their field as a rigorous science. The behaviorist movement dominated psychology and urged researchers to study only observable and measurable behaviors.

An American psychologist named Harry Harlow, however, became interested in studying a topic that was not so easy to quantify and measure—love.

In a series of controversial experiments conducted during the 1960s, Harlow demonstrated the powerful effects of love and in particular, the absence of love.﻿﻿ By showing the devastating effects of deprivation on young rhesus monkeys, Harlow revealed the importance of a caregiver's love for healthy childhood development.

Harlow's experiments were often unethical and shockingly cruel, yet they uncovered fundamental truths that have heavily influenced our understanding of child development.

The Wire Mother Experiment

Harlow noted that very little attention had been devoted to the experimental research of love. "Because of the dearth of experimentation, theories about the fundamental nature of affection have evolved at the level of observation, intuition, and discerning guesswork, whether these have been proposed by psychologists, sociologists, anthropologists, physicians, or psychoanalysts," he noted.

Many of the existing theories of love centered on the idea that the earliest attachment between a mother and child was merely a means for the child to obtain food, relieve thirst, and avoid pain. Harlow, however, believed that this behavioral view of mother-child attachments was an inadequate explanation.

Harlow’s most famous experiment involved giving young rhesus monkeys a choice between two different "mothers." One was made of soft terrycloth but provided no food. The other was made of wire but provided nourishment from an attached baby bottle.

Harlow removed young monkeys from their natural mothers a few hours after birth and left them to be "raised" by these mother surrogates. The experiment demonstrated that the baby monkeys spent significantly more time with their cloth mother than with their wire mother. In other words, the infant monkeys went to the wire mother only for food but preferred to spend their time with the soft, comforting cloth mother when they were not eating.﻿﻿

"These data make it obvious that contact comfort is a variable of overwhelming importance in the development of affectional response, whereas lactation is a variable of negligible importance," Harlow explained.﻿﻿

Fear, Security, and Attachment

In a later experiment, Harlow demonstrated that young monkeys would also turn to their cloth surrogate mother for comfort and security. Using a "strange situation" technique similar to the one created by attachment researcher Mary Ainsworth, Harlow allowed the young monkeys to explore a room either in the presence of their surrogate mother or in her absence. Monkeys in the presence of their mother would use her as a secure base to explore the room.

When the surrogate mothers were removed from the room, the effects were dramatic. The young monkeys no longer had their secure base for exploration and would often freeze up, crouch, rock, scream, and cry.

Harlow’s experiments offered irrefutable proof that love is vital for normal childhood development. Additional experiments by Harlow revealed the long-term devastation caused by deprivation, leading to profound psychological and emotional distress and even death.

The Impact of Harlow’s Research

Harlow’s work, as well as important research by psychologists John Bowlby and Mary Ainsworth, helped influence key changes in how orphanages, adoption agencies, social services groups, and child care providers approached the care of children.﻿﻿

While Harry Harlow's work led to acclaim and generated a wealth of research on love, affection, and interpersonal relationships, his own personal life soon began to crumble. After the terminal illness of his wife, he became engulfed by alcoholism and depression, eventually becoming estranged from his own children. Colleagues frequently described him as sarcastic, mean-spirited, misanthropic, chauvinistic, and cruel. Despite the turmoil that marked his later personal life, Harlow's enduring legacy reinforced the importance of emotional support, affection, and love in the development of children.

A Word From Verywell

Harlow's work was controversial in his own time and continues to draw criticism today. While such experiments present major ethical dilemmas, his work helped inspire a shift in the way that we think about children and development and helped researchers better understand both the nature and importance of love.