But, things change dramatically, and not for the better, when our wild cousins are utilized in research or entertainment, or are forced into a life as a pet in someone's household.
For them, every natural instinct has been suppressed. They don't mature with their mothers' fur grasped in their tiny hands, and they don't have the troop's wisdom to guide them. Instead, they are kept in steel cages or wrapped in human clothes and fed human food, most often without ever seeing another of their own kind. Those raised for the pet trade suffer an even greater tragedy, as they are stolen from their mothers at only a few days old.
You will likely never see a wild primate bite himself. You will never see a normal, wild macaque spin in circles while trying to remove his own foot. You will never see a wild primate huddle in a corner, chewing on his arm.
But, these behaviors are common in those raised unnaturally by humans who confine them.
Denied a natural upbringing, along with a lack of consistent and natural enrichment, they lead lives of frustration and boredom, which adds to an already damaged psyche. This frustration must have an outlet, and they learn to cope with their anxiety by biting, spinning, pulling hair, and other unnatural behaviors that serve to release stress.