It's estimated there are more than 700 pet chimpanzees currently living in the United States, many of them smuggled illegally from Africa. Should any of these 700 chimp owners grow disenchanted as their adorable infant quickly turns into a moody 200-pound ape -- and many will -- they'll likely call a local zoo or wildlife organization.

Though these chimps would certainly be safer in the hands of professionals, they're unlikely to ever adjust well to getting along with other non-human primates. New research suggests chimps raised by humans exhibit lifelong behavioral problems, and have difficulties being reintroduced to life with other chimps.

Most objections to wild animals being raised as pets are made on moral or ethical grounds. Biologists Stephen Ross and Hani Freeman, from the Fisher Center for the Study and Conservation of Apes at Lincoln Park Zoo in Chicago, wanted to approach the issue more scientifically. The potential for the spread of disease and risk of violence are already well documented reasons why raising a chimp in one's home is scientifically unwise. So Ross and Freeman elected to study the social and behavioral effects of domestic or human rearing of chimps.

They studied 60 chimpanzees from accredited zoos or sanctuaries, more than half of which were former pets or performers. But rather than just divide the chimps into two categories, human-raised and not, Ross and Freeman developed a graded scale by which to measure the level of human-exposure called the Chimpanzee-Human Interaction Index.

The researchers found that chimps taken from their mothers almost immediately and raised mostly by humans were more likely to exhibit abnormal behaviors -- coprophagy (eating one's own feces), abnormal movement, abnormal body posturing and hair plucking -- and less likely to participate in social grooming activities.

"Chimpanzees raised to be pets or performers have very atypical lives," Ross told Wired. "They don't see other chimpanzees; they aren't exposed to chimpanzee culture; they're in a completely human world."

The most significant behavioral difference, Ross and Freeman found, was that chimps raised by humans were much less likely to participate in social grooming. The researchers said this was even the case for human-raised chimps who had been reintroduced and living among other chimps for some time.

"Grooming is the glue that holds chimpanzee society together," explained Ross. "We found chimpanzees that were around humans a lot early in life tended not to do a lot of this behavior, even much later, after they learned to live with other chimpanzees. They just weren't good at maintaining these social bonds, and that was expressed by these lower rates of grooming."

The work of Ross and Freeman was published this week in the free online journal PeerJ.