Chimps who are removed from their mothers early in life and raised by humans as pets or performers are more likely to develop behavioral and social problems, according to new research.


Can't say I'm surprised, but it's good to see work being done in this area. It's well documented, for example, that infant chimps, when removed from their mothers, exhibit immediate psychological issues. Separate work by Emory University biopsychologist Lori Marino shows how and why certain animals, such as great apes and cetaceans, suffer and sometimes go mad in captivity. What's more, and as near-definitive proof that chimps experience psychological and emotional states similar to humans, ex-lab chimps show remarkable improvement after treatment with antidepressants.


The latest research was led by Steve Ross, director of the Fisher Center for the Study and Conservation of Apes at Lincoln Park Zoo. During the 14 month study, 60 chimps with a range of personal histories were carefully monitored. All of them were living in a variety of zoos accredited by the Association of Zoos and Aquariums (AZA) and sanctuaries participating in the North American Primate Sanctuary Alliance (NAPSA).

The results now appear in the latest edition of PeerJ. A clip from the abstract offers an excellent summary of the researchers' findings:

In order to account for the influence of both human and conspecific early exposure to later behavior, we collected 1385 [hours] of data on 60 chimpanzees, of which 36 were former pets or performers, currently housed at accredited zoos or sanctuaries. We developed a unique metric, the Chimpanzee-Human Interaction (CHI) Index that represented a continuous measure of the proportion of human and chimpanzee exposure subjects experienced and here focused on their exposure during the first four years of life. We found that chimpanzees who experienced less exposure to other chimpanzees as infants showed a lower frequency of grooming and sexual behaviors later in life which can influence social dynamics within groups. We also found chimpanzees who experienced more exposure to other chimpanzees as infants showed a higher frequency of coprophagy [the eating of feces], suggesting coprophagy could be a socially-learned behavior. These results help characterize some of the long-term effects borne by chimpanzees maintained as pets and performers and may help inform managers seeking to integrate these types of chimpanzees into larger social groups, as in zoos and sanctuaries. In addition, these results highlight the necessity of taking into account the time-weighted influence of human and conspecific interactions when assessing the impact that humans can have on animals living in captivity.


The study is one of the first attempts to take a holistic approach to understanding how both human and chimp exposure can affect behavioral development and how those effects are expressed much later in life.

"One of the startling aspects of these findings is that these behavioral effects are so long-lasting," noted Ross in an accompanying statement. "Chimpanzees which have found new homes in accredited zoos and good sanctuaries continue to demonstrate behavioral patterns that differentiate themselves from more appropriately-reared individuals. As a result, the process of integrating them with other chimpanzees can be challenging, stressful and even dangerous at times."


He says that denying chimps access to members of their own species during the critical infant period results in behavioral outcomes that "last a lifetime." And even with the best possible care and by the best intentioned humans adults, they simply can't fit in with the other chimpanzees.

Read the entire study at PeerJ: "The impact of atypical early histories on pet or performer chimpanzees".

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