WIKIMEDIA, THOMAS LERSCHTests of spatial memory, tool use, communication, and other cognitive abilities in chimpanzees have revealed that aspects of intelligence, including general intelligence, are inherited. The results, published today (July 10) in Current Biology, complement similar findings from human studies, and lend support to the theory of general intelligence—wherein an individual’s overall cognitive prowess influences his or her more specific abilities.
“This is really major evidence that . . . those estimates of the heritability of human intelligence are probably dead on,” said Alexander Weiss, a psychologist at the University of Edinburgh in the U.K., who was not involved in the study. “Anyone sensible and objective looking at this, who had any doubts about the heritability of human intelligence . . . should put those worries to rest.”
Although a great deal of evidence suggests that a person’s brainpower is in large part attributable to that of their parents, some believe environmental factors, such as socioeconomic status, are more important than genetics, said Weiss. And resolving that debate hasn’t been easy. “One of the challenges in the human intelligence literature is that it is very difficult to isolate the role of genetics relative to the role of non-genetic factors,” said Bill Hopkins, a professor at the Neuroscience Institute of Georgia State University, who led the new research.
For example, “intelligent people tend to have more books in their homes and therefore their children tend to read more, which leads them, at least some evidence suggests, to be more intelligent,” he said. “So the question is: Are they intelligent because their parents are intelligent and they have passed those genes on, or are they smarter because their parents are providing more environmental input?”
“Chimps [in captivity] don’t have things like parents sticking books in front of them,” he added, so they allow genetic investigations of intelligence “without the confounding effects of these variables that are difficult to control in human societies.”
In Hopkins’s study, 99 chimps were subjected to 13 different tests covering a range of specific cognitive skills. The team then applied a statistical process called a principal component analysis (PCA), which essentially identified links between the individual tests. That is, the PCA determined whether an animal’s ability in one test was linked to its ability in any of the other tests. If such links were found, those tests were lumped together into one subgroup, or component. From this analysis, the 13 cognitive tests were divided into four components.
After the tests were completed, each chimp had scores both for overall (general) intelligence—calculated from all 13 tests—and for each of the four components. Tallying these intelligence scores with the chimps’ known relatedness to one another, the team confirmed that general intelligence scores were heritable, as were the scores for two of the four components—those that included spatial memory and communication ability.
“Some people think you can partition or parcellate intelligence . . . so you have a logical arithmetic one, and a language one, and a music one,” said Hopkins. But, said Weiss, “[Hopkins’s study] is a really strong piece of evidence in favor of general intelligence—the view that there is a single underlying factor for intelligence.”
Interestingly, a human genome-wide association study (GWAS) published in Nature Communications this week (July 8) also provided evidence for general intelligence, showing that approximately half of the genetic variations linked with ability in mathematics are also those linked with ability in language.
Hopkins said that, with enough animals, similar GWASs could be performed in chimpanzees. Candidate genes could then be compared between humans and chimps to see how the genetic component of the two species’ intelligence has evolved.
Ultimately, it is probably no surprise that, like human intelligence, chimp intelligence is heritable, given that “we were the same species for 23 million years,” said Sally Boyson, a professor of psychology at Ohio State University. However, it had never actually been confirmed, she said. “We can surmise, we can speculate, we can think, ‘Oh, probably,’ but [Hopkins’s group] went out and did it.”
W.D. Hopkins et al., “Chimpanzee intelligence is heritable,” Current Biology, 24:1-4, 2014.
O.S.P. Davis et al., “The correlation between reading and mathematics ability at age twelve has a substantial genetic component,” Nature Communications, 5:4204, doi:10.1038/ncomms5204, 2014.