Studies show that early stress in monkey or human infants can lead to long-term social and behavioral problems. Now, Judy Cameron of the University of Pittsburgh and the Oregon National Primate Research Center at Oregon Health Sciences University in Portland finds that the timing of separation of an infant monkey from its mother predicts what kind of social problems it will develop.
Monkeys who are reared in a normal social group but whose mothers are removed when they are just a week old were less social all the way into adulthood, while those who were separated at one month tended to demand more social attention and act out. (A one-week-old monkey is equivalent to a one-month-old baby, and a one-month-old monkey is similar to a four-month-old human.)
If, after separation, the young monkeys were moved to a new monkey group, they became more agitated than animals that had been reared by their mothers. The monkeys separated at one month tended to eat more and play less than other monkeys, a behavioral pattern that was seen only in the monkeys that had experienced this early-life trauma.
If the infants separated at one week were put in the care of a surrogate mom when they were between one and three months of age, they seemed to recover and develop normally. But thereafter it seems to be too late. “There seems to be a window for effective therapy,” Cameron says.
People should be careful about translating monkey research into humans, Cameron says, but she thinks the work does suggest interesting topics for study, such as whether people who eat when stressed had an early-life trauma.
Monkeys such as these were studied to determine the effects of separation of an offspring from its mother. Behavioral responses varied depending on how old the monkeys were when they were separated. © Oregon National Primate Research Center