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Harry F. Harlow

( 1906-1981 )



Harry F. Harlow was an American Psychologist who provided a new understanding of human behavior and development through studies of social behavior of monkeys. His research contributions (in the areas of learning, motivation, and affection) have major relevance for general and child psychology.

Harlow obtained both his BA and PhD in Psychology from Stanford University. Upon completion of his PhD, Harlow joined the psychology staff at the University of Wisconsin (Madison). He was a modest, brilliant man who enjoyed spending time with students and took special pride in teaching introductory psychology courses. Nearly forty students obtained their PhD under his direction.


Professor Harlow's research developed an abundant supply of primate learning tests and tasks that became standards in the field. In general, Harlow wanted to prove to the psychology community that primate research could contribute to the understanding of important clinical issues without having to be molecular in nature. His theory hinged on the universal need for contact. Harlow's famous wire/cloth "mother" monkey studies demonstrated that the need for affection created a stronger bond between mother and infant than did physical needs (food).

Harlow was a member several Science and Psychological Associations, including the American Psychological Association, National Academy of Arts & Sciences, and Sigma Xi. He was a national lecturer and also a consultant to the Army's Scientific Advisory Panel. During his career, he was recognized with several distinctions, including: Howard Crosby Warren Medal (1956), National Medal of Science (1967), and Gold Medal from American Psychological Foundation (1973). Much of his primate research regarding social separation, affection, attachment, love, learning, and early life behaviors was published.

Harlow died in 1981, at the age of 75. His life work provided a developmental framework based on data results rather than convoluted theories with limited empirical support.

Harry Harlow received his BA and PhD (1930) in psychology from Stanford University and immediately joined the faculty at the University of Wisconsin. Within a year, he had established the Psychology Primate Lab, which continued expanding until it joined with the Wisconsin Regional Primate Lab in 1964. Harlow became the director of the merged research center. Among the scientists to work there was Abraham Maslow, who would later establish the school of humanistic psychology.

Harlow was intrigued by love. He questioned the theories then current which stated that love began as a feeding bond with the mother and applied by extension to other family members. Other theories claimed that humans and other social animals lived in organized societies simply to regularize sexual contact. Starting in 1957, Harlow worked with rhesus monkeys, which are more mature at birth than humans, but like human babies show a range of emotions and need to be nursed. He took infant monkeys away from their real mothers, giving them instead two artificial mothers, one model made of wire and the other made of cloth. The wire model was outfitted with a bottle to feed the baby monkey. But the babies rarely stayed with the wire model longer than it took to get the necessary food. They clearly preferred cuddling with the softer cloth model, especially if they were scared. (When the cloth model had the bottle, they didn't go to the wire model at all.)

In another study, Harlow found that young monkeys reared with live mothers and young peers easily learned to play and socialize with other young monkeys. Those with cloth mothers were slower, but seemed to catch up socially by about a year. Babies raised with real mothers but no playmates were often fearful or inappropriately aggressive. Baby monkeys without playmates or real mothers became socially incompetent, and when older, were often unsuccessful at mating. Those unsocial females that did have babies were neglectful of them. From his studies, Harlow concluded that sex alone did not drive societies, nor did mother love enable individual social relations. Rather, normal sexual and parental behavior depended on a wide array of affectional ties with peers and family early in life.

Harlow's theories, of course, raised many more questions that other researchers would tackle. Interestingly, his scientific study of love came at a time when science was generally held in high regard. Perhaps it could even reveal the mysteries of love.


In Harlow's initial experiments, infant monkeys were separated from their mothers at six to twelve hours after birth and were raised instead with substitute or "surrogate" mothers made either of heavy wire mesh or of wood covered with cloth. Both mothers were the same size, but the wire mother had no soft surfaces while the other mother was cuddly – covered with foam rubber and soft terry cloth. Both mothers were also warmed by an electric light placed inside them.

image In one experiment both types of surrogates were present in the cage, but only one was equipped with a nipple from which the infant could nurse. Some infants received nourishment from the wire mother, and others were fed from the cloth mother. Even when the wire mother was the source of nourishment (and a source of warmth provided by the electric light), the infant monkey spent a greater amount of time clinging to the cloth surrogate. These results led researchers to believe the need for closeness and affection goes deeper than a need for warmth.

These monkeys raised by the dummy mothers engaged in strange behavioral patterns later in their adult life. Some sat clutching themselves, rocking constantly back and forth; a stereotypical behavior pattern for excessive and misdirected aggression. Normal sexual behaviors were replaced my misdirected and atypical patterns: isolate females ignored approaching normal males, while isolate males made inaccurate attempts to copulate with normal females.


As parents, these isolate female monkeys (the "motherless mothers" as Harlow called them) were either negligent or abusive. Negligent mothers did not nurse, comfort, or protect their young, nor did they harm them. The abusive mothers violently bit or otherwise injured their babies, to the point that many of them died. Deprivation of emotional bonds to live mother monkeys (as infant monkeys) these (now adult) monkeys were unable to create a secure attachment with their own offspring. (Principles of General Psychology, 1980, John Wiley and Sons).




Harlow's research suggested the importance of mother/child bonding. Not only does the child look to his/her mother for basic needs such as food, safety, and warmth, but he also needs to feel love, acceptance, and affection from the caregiver. His findings show some long-term psychological physical effects of delinquent or inadequate attentiveness to child needs.



Harlow also did learning research with his monkeys. His theory, "Learning to Learn", described the ability of animals to slowly learn a general rule that could then be applied to rapidly solve new problem sets.

Harlow presented the monkey with two stimuli (a red block and a thimble, for example); one was predetermined "correct" and reinforced with food (red block) and the other was "incorrect" and not reinforced with food (thimble). After each selection, the objects were replaced and the monkey again chose a stimulus. Each trial reinforced the same stimulus (red block). The monkey had a 50% chance of being "correct" on each trial, however, he could increase his chances by adopting the win-stay, lose-shiftstrategy. For example, if the monkey chose the thimble and was not reinforced, he should shift to the red block for the reinforcer. If, however, he correctly selected the red block and was reinforced, he should stay with the reinforced stimulus and choose the same stimulus next time.

The monkey continued throughout a series of six trials with eight pairs of stimuli (learning sets). Harlow found the monkeys to be averaging approximately 75% correct responses by the sixth trial of the eighth set. He then began to look at the animal's behavior during the second trial. He found the monkeys to implement the stay or shift strategy on the second trial of the six-trial set, which means the animals did not relearn the strategy with each new stimuli set, they instead applied the rule they had already learned. After 250-plus trials, the monkeys were about 98% correct on the second through the sixth trials with each new stimuli set.

Harlow's learning research demonstrates that animals, like humans, are able to learn to apply strategies or rules to situations to help them solve problems.


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