Nature and nurture both play a role in human intelligence. How large a role each plays, however, is a matter of considerable debate in a number of fields. Measuring the role of upbringing in human intelligence is difficult. Human society is incredibly complex and any number of factors could conceivably play a role in mental development. Those factors, as well as the definition of intelligence and the means for measuring it also vary between cultures.

In a paper published in the latest issue of Current Biology, researchers did the next best thing. They measured intelligence in humanity’s closest living relative, the chimpanzee. They found that many cognitive abilities in chimps appear to be primarily a matter of genetics and are impacted only slightly by environmental factors.

“Intelligence runs in families. The suggestion here is that genes play a really important role in their performance on tasks while non-genetic factors didn’t seem to explain a lot. So that’s new,” said Dr. William Hopkins, professor in the Center for Behavioral Neuroscience at Georgia State and research scientist in the Yerkes National Primate Research Center at Emory University in a statement.

Chimpanzees are highly intelligent animals but they do not have the social and cultural influences that make the impacts of nurture on human intelligence difficult to measure.

“Chimps offer a really simple way of thinking about how genes might influence intelligence without, in essence, the baggage of these other mechanisms that are confounded with genes in research on human intelligence,” Hopkins said.

The researchers had 99 chimps, between 9 and 54 years of age, complete 13 tasks, designed to test their abilities. Using quantitative genetic analysis, Hopkins and his team also tested the relatedness of the chimpanzees and applied that information to the similarities and differences in the animals’ performance on the tests.

Genes appeared to be a significant factor in the chimpanzees’ performance on several tests, regardless of how or where they were raised.

The traditional view, based on the work of behaviorists such as B.F. Skinner and Ivan Pavlov, has held that the environment and how behavior is reinforced, positively or negatively, is essential to an animal’s performance on tests. In the most famous example Pavlov rang a bell when he fed his dogs and, after a short time, found that the animals began to drool at the sound of the bell, whether there was any food being offered or not.

Hopkins study seems to refute the classical analysis, or at least offer a valuable supplement to it.

“In our case, at least, it suggests that purely environmental explanations don’t really seem to tell the whole story. Genes matter as well,” said Hopkins.

The researchers are also interested in studying the similarities between the structure of chimpanzee intelligence and the structure of human intelligence.

“We wanted to see if we gave a sample of chimpanzees a large array of tasks. Would we find essentially some organization in their abilities that made sense. The bottom line is that chimp intelligence looks somewhat like the structure of human intelligence,” said Hopkins.

The researchers would like to expand the study using a larger number of chimpanzees as well as study the genetic differences which occurred in the brain between chimpanzees and humans. It is possible that this information could shed light on how human intelligence evolved and why it appears to be so much more advanced than that of our closest relatives.