In Harry Harlow’s rhesus-monkey attachment experiment, infant monkeys preferred a cloth mother for comfort.
Beginning in the 1950s, psychologist Harry Harlow and his colleagues separated infant rhesus macaques from their biological mothers and offered them surrogate “mothers.” One surrogate was made of bare wire and could provide milk; the other was covered in soft terry cloth and did not necessarily provide food. The infants spent much more time clinging to the cloth-covered surrogate, especially when they were frightened.
The findings challenged the idea that infant attachment was mainly based on feeding. Harlow argued that physical contact comfort was a powerful part of the bond between infants and caregivers. The monkeys often visited the wire surrogate only long enough to feed before returning to the cloth one.
Harlow’s later deprivation studies caused severe distress and are now regarded as ethically unacceptable. His work influenced developmental psychology, but it also helped intensify debate about animal welfare and the limits of laboratory research.