Inexplicably, the mere mention of the word chimpanzee sends many people into giggle fits, especially in the context of owning one as a pet, dressing it up, etc. Unfortunately, it’s no laughing matter: A study conducted by the Lincoln Park Zoo found that chimps who begin life as pets or performers suffer serious social and behavior deficiencies later in life.

“One of the startling aspects of these findings is that these behavioral effects are so long-lasting,” said Steve Ross, PhD, director of the Fisher Center for the Study and Conservation of Apes at Lincoln Park Zoo. “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.”

The problems are most pronounced when chimpanzees are raised primarily by humans during the first four years of their lives (those with a more conventional upbringing are less affected). When re-integrated with their own species, human-raised chimps are less engaged in social activities, like grooming. These behaviors are critical to normal socialization, and not participating can alienate chimps and make integration difficult.

What’s worse, it can take years or even decades for these issues to manifest.

Shockingly, it is legal in most of the U.S. to own chimps as pets, despite them being endangered and fearsomely powerful, dangerous animals in the wrong circumstances. The study, which is the first to take a more holistic view of how human interaction affects chimpanzees, will hopefully persuade lawmakers to outlaw or severely restrict private chimpanzee ownership.

“Chimpanzees are incredibly intelligent and sensitive animals,” Ross said. “Denying them access to members of their own species, during the critical infanthood period, results in behavioral outcomes that last a lifetime. Even with the best possible care as adults, they often can’t fit in with the other chimpanzees.”