Now, a new study suggests that -- like humans -- a chimpanzee's parents and their genes are at least half responsible for determining its smarts.
"Genes matter," confirmed William Hopkins, co-author of the new study on the subject and full-time neuroscientist at Georgia State University in Atlanta.
The chimpanzee intelligence study was published this week in the journal Current Biology.
"We have what we would call a smart chimp, and chimps we'd call not so smart," Hopkins told LiveScience. "We were able to explain a lot of that variability by who was related to each other."
Hopkins and his colleagues arrived at their conclusions after putting 99 captive chimpanzees through a battery of tests designed to measure intelligence. The 99 chimps were part of an expansive family tree, including near and distant relatives, so researchers were able to compare intelligence scores to genetic relatedness.
"It doesn't mean that [genes] are the only factor determining cognitive abilities, but they cannot be ignored," Hopkins said.
The study found spacial understanding and social intelligence to be particularly heritable, but that wasn't the case for tool use, which may be an acquired skill. Because the study suggests only half of chimp intelligence differentiation can be explained by nature, there's still plenty of room for nurture to work its magic.