Development of infant social isolate monkeys (Macaca mulatta) in their isolation environments

Abstract

This study was designed to more clearly define thetreatment of early social isolation. Four newborn infant rhesus monkeys, (Macaca mulatta) were raised in social isolation and their behavioral developmentduring their sojourn in isolation was compared to the behavioral development of four controls which were reared by mothers. The controls were matched with the isolates for age and sex and both groups were studied for 30 weeks. The following conclusions resulted from this study: 1. Infant rhesus monkeys raised in laboratory cages do not display facial expressions very frequently, whether they are isolate-reared or alone with a mother. A search of the literature indicated that facial expressions do not occur frequently early in life even when peers are provided. 2. Isolates spent more time looking at human observers, at the nonsocial environment, and at themselves than did controls while controls looked a their mothers or slept. 3. Isolates showed more walking and more manual exploration of the cage and of themselves than did controls but controls did more cage climbing and jumping, and the latter was often oriented toward the mother. The isolates moved more slowly and awkwardly than did the controls. 4. Isolates did not make as extensive use of towels in their cages as we had expected. Controls were in contact with their mothers much more frequently than isolates were in contact with their towels. 5. Abnormal movements such as rocking, self-grasping, and autoeroticism, appeared in the isolates before the end of thefirst month. Thus, the first month of life is evidently extremely crucial for the development of abnormal behavior. Though many abnormal movements first appear during the first month, each individual isolate apparently does not settle down to his own favorite type of weirdness until well after seven months of age.