Human beings are social creatures. We are social not just in the trivial sense that we like company, and not just in the obvious sense that we each depend on others. We are social in a more elemental way: simply to exist as a normal human being requires interaction with other people.
Children provide the clearest demonstration of this fact, although it was slow to be accepted. Well into the nineteen-fifties, psychologists were encouraging parents to give children less attention and affection, in order to encourage independence. Then Harry Harlow, a professor of psychology at the University of Wisconsin at Madison, produced a series of influential studies involving baby rhesus monkeys.
He happened upon the findings in the mid-fifties, when he decided to save money for his primate-research laboratory by breeding his own lab monkeys instead of importing them from India. Because he didn’t know how to raise infant monkeys, he cared for them the way hospitals of the era cared for human infants—in nurseries, with plenty of food, warm blankets, some toys, and in isolation from other infants to prevent the spread of infection. The monkeys grew up sturdy, disease-free, and larger than those from the wild. Yet they were also profoundly disturbed, given to staring blankly and rocking in place for long periods, circling their cages repetitively, and mutilating themselves.
At first, Harlow and his graduate students couldn’t figure out what the problem was. They considered factors such a...