Temperamental behaviors measured during the first months of life are predictive of aggression in group housed rhesus macaques (Macaca mulatta)
Chaffin, Andrew C.; Barr, Christina S.; Higley, James D.
Abstract
Temperament is thought to be the foundation for personality and subsequent behaviors later in life. To assess early temperamental variables that place individuals at risk for aggression later in life, this laboratory-based study examined infant behavior in group housed infant rhesus macaques (Macaca mulatta). The subjects were 52 mother-reared subjects. Behavior was assessed from the first through the eighth months of life using objective behavioral measures. Two 5-minute sessions were recorded for subjects each week over 8 months and the average rate of each of the 25 behaviors measured was the dependent measure. A test of the same subjects 2-4 years later measured the dependent variable, aggression, using the Fairbank’s Intruder Challenge Test, when subjects were 3-5 years of age. Results: Four behaviors exhibited a statistically significant ability to predict aggression. Statistically significant correlations were found for activity-oriented behaviors of environmental exploration, approach by infant, and leave by infant, as well as the social variable, socialize with individuals other than mother, with a modest positive r-value between .273 and .357. This activity-oriented trait may reflect hyperactive tendencies that have been shown in humans to increase the risk for aggression. This study suggests that objective measurements of activity levels in infant rhesus monkeys can be a predictive variable in determining later levels of aggression.