Atypical early histories predict lower extraversion in captive chimpanzees.

Although much research has been conducted to understand personality development in humans, there remain substantial gaps in our understanding of these processes, particularly in relation to social influences. As such, investigations into personality development in our closest living relative, the chimpanzee, may provide useful insight. We evaluated the impact of early social exposure (to both humans and conspecifics) on personality development by studying 88 chimpanzees, including former pets and entertainers, living in accredited zoos and sanctuaries. During infancy, subjects varied in the amount of time spent with conspecifics compared with humans. Caregivers familiar with the chimpanzees rated them using a modified version of the Hominoid Personality Questionnaire (HPQ) and the ratings were found to have strong inter-rater reliability. We used the published structure of the HPQ to evaluate our results in relation to differences in early life experience. Chimpanzees who as infants spent less time with conspecifics were rated as lower in Extraversion later in life in comparison with chimpanzees who as infants spent more time with conspecifics. These results suggest that a broad range of social influences should be considered when evaluating the impact of early social environment on later personality expression.