Abstract
Experiences during early development are influential on the lives of human and non-human primates into adulthood. The population of captive chimpanzees in the USA can provide insight into this relationship, as collectively they have experienced a wide range of exposure to both conspecifics (those raised in natal groups) and humans (those raised as personal pets or performers). Our study investigated chimpanzee exposure to humans using a continuous measure of categorization, the chimpanzee–human interaction index, and the relationship between this experience and cortisol concentrations in adulthood. Historical records and hair samples were collected from 60 chimpanzees which were socially housed in 13 zoos and sanctuaries. We found that more human exposure throughout the life of a chimpanzee was associated with higher hair cortisol concentrations in adulthood. Sex was also a significant factor affecting cortisol concentration, with male chimpanzees having higher cortisol concentrations than female chimpanzees. These results build upon the extensive literature about aversive effects of atypical social histories for chimpanzees and emphasize to managers the importance of monitoring potential negative health consequences and social deficits these individuals may exhibit.
Highlights
Experiences during infancy and the juvenile stage are influential on the lives of human and non-human primates due to their prolonged developmental periods before reaching sexual maturity [1,2]
Since sociality is an important part of chimpanzee life, we aimed to investigate whether the social differences would be reflected physiologically by differences in cortisol levels between chimpanzees with differing degrees of conspecific exposure throughout their lives
Average log10 cortisol concentrations were negatively correlated with chimpanzee–human interaction index (CHI) (r = −0.32, p < 0.05) such that the more conspecific exposure that chimpanzees experienced, the lower the average cortisol concentrations
Summary
Experiences during infancy and the juvenile stage are influential on the lives of human and non-human primates due to their prolonged developmental periods before reaching sexual maturity [1,2]. Spend infancy in direct contact with their mother and other conspecifics, both kin and non-kin. This 2 period of dependence on their mother as their source of food and protection provides opportunities to learn species-typical behaviours through observation, physical contact and communication, which contribute to reproductive and social competence as adults. For many primates, these opportunities for learning continue through juvenility as they become more independent and begin to interact with others of their own species [3]
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