Infant monkeys removed from their biological mothers and given 2 surrogates (one made from wire and providing food, one made from cloth but doesn’t provide food)
spent more time with the cloth mother and clung to them when frightened
Continued his research on motherless monkeys as they grew up to see if maternal deprivation had an effect
They developed abnormally: froze or fled when approached by other monkeys, didn’t show normal mating behaviour, bred less, mothers neglected their young or killed them
found a critical period - 90 days