When Harry Harlow completed his cloth mother experiments, he concluded that “mother love is indispensable”, and that it provides the infant a safe haven from which to explore an often dangerous world. He also became interested in exploring the limits of that love.
“Knowing that a mother could give an infant love and security, we thought many years ago that we could produce anaclitic (dependency) depression by allowing baby monkeys to attach to cloth surrogate mothers who could become monsters.”
Harlow built four monster mothers, all modified cloth mothers. The first would blast the clinging baby with highly pressurized air. “It would blow the animal’s skin practically off its body”, he wrote.
The second mother would shake so hard that “the baby’s head and teeth would rattle”. Neither of the first two monster mothers were able to dissuade their babies; the little monkeys “simply clung tighter and tighter to the mother, because a frightened infant clings to its mother at all costs.”
The third mother had a wire frame embedded in its body; the experimenter would release the frame, which would thrust out suddenly and propel the infant off its mother. The fourth mother Harlow called the ‘porcupine mother’: she would eject brass ‘spikes’ (which were dulled) all over her body, again compelling the infant to release her hold.
While these second two mothers were able to literally force their babies to relinquish their hold on them, neither induced Harlow’s desired ‘psychopathology’; the babies would simply wait for the offending apparatus to recede back into its mother’s body, and then cling to her again. Harlow was unsurprised by this result; he wrote, “the only recourse of an injured or rebuked child – monkey or human – is to make intimate contact with the mother at any cost.”
Harlow did eventually succeed in inducing psychopathology in monkeys, through social isolation. By taking infant female monkeys and keeping them in total isolation for the first six to nine months of their lives, he created adult female monkeys two-thirds of whom “turned out to be inadequate or evil mothers”. Evil is not a word often applied to non-human animals; Harlow uses it repeatedly and deliberately. These mothers might completely ignore their babies; worse, many of them displayed behaviors that were “brutal or lethal” towards their young. They would crush the baby’s head in their teeth, or they would smash the baby’s head against the ground and drag it along the floor of the cage.
Harlow may have caused psychopathology, but he couldn’t exterminate mother love. The infants of these evil mothers “never gave up unless they were killed. The babies went back and back and back to their mothers, trying forever to attach”. If the baby survived, this often worked:
“In a manner of speaking, the infants healed the mothers. And these mothers, who eventually became maternalized by their first babies, were, on the second, third, or fourth pregnancies, for all practical purposes, perfectly normal mothers.”
Image taken from Harlow’s 1970 paper, ‘Induced Psychopathology in Monkeys’
For a very good scientific biography of Harlow and explanation of his social and scientific context, read Deborah Blum’s Love at Goon Park: Harry Harlow and the Science of Affection.