(my bold)

There were also stark differences between the levels of aggression among the bonobo groups in different zoos — more so than in chimps. “Our findings contribute to a growing body of evidence suggesting that behavioral patterns in Pan, including aggression, may be more influenced by group identity than by species-wide traits,” the authors wrote.

Zoos offer an interesting perspective on ape behavior. Some researchers argue that chimpanzees are more warlike because food was less available on their side on the Congo River and they had to compete with gorillas for resources. Conversely, bonobos had more food and fewer predators.

In zoos, these environmental factors are no longer at play. “The main benefit is that you take the two species out of their ecology and you really get the behavioral differences that are due to, for example, genetic changes that have occurred since the split from each other,” Staes said.