Individual differences in young rhesus monkeys: Consistency and change

At 1 year and 2.5 years of age, rhesus monkeys were removed from the colony to a strange situation. Upon introduction, each monkey was watched for 2 hr, given a series of behavioural tests, and watched again six days after introduction. Activity increased with age, as did readiness to approach a ball. Time spent looking at a mirror decreased with age. Although test measures were reliable at each age, there was no significantly positive...