A study conducted by researchers from the Yerkes National Primate Research Center in Atlanta found out half of chimp intelligence is due to genes and the other half is due to environmental factors. 

William Hopkins, lead author of the study and a primatologist from the Yerkes National Primate Research Center, and his colleagues looked at the mental capabilities of 99 chimpanzees in captivity. They also designed a series of 13 tests to measure the chimps' ability to deal with their physical environment, reaction to stimuli, and intelligence in using simple tools.

The chimps all came from a big family tree, with some being full siblings and some having fourth to fifth cousins. This expansive genetic map gave the researchers data to calculate how genes manifest in a particular family.

They found out that there were two types of tasks that could be passed on through the genes; one was spatial cognition, a capability that enables humans to manage easy and challenging cognitive tasks in daily life; and dealing with the physical environment. The researchers observed some chimps making kissing sounds and clapping their hands just to get attention.

"This one is a real measure of intelligence and innovative behavior," Hopkins said to the National Geographic.

Findings of the study supported the social brain hypothesis, a theory in which human intelligence was a by-product of our evolution that helped our ancestors survive and prolong relationships in a large and social group.

Although this study focused on the effects of genes in the chimps' intelligence, Hopkins and his team were also able to observe some strong environmental cues that may affect their intelligence.

Ajit Varki, professor of medicine from the University of California in San Diego, commented that the results of this research were very similar to human studies.

"In the impoverished and stereotyped setting of long-term captivity, the critical influence of environmental variability could be markedly blunted," Varki told the National Geographic.

Further details of this study were published in the July 10 issue of Current Biology.