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If chimps inherit their intelligence, does that prove humans do, too?

by Rowan Hooper

Some people are smarter than others. And though animal intelligence is far less well studied, it turns out that within a particular population, say of chimpanzees, some animals are smarter than others, too — and these differences are heritable. To put it another way, some chimps’ mothers are smarter than other chimps’ mothers.

There are few thornier subjects than human intelligence, and specifically, the idea that it has a genetic basis. If we have been concerned by facing up to the evidence in humans, will we accept it any more easily in our chimp cousins? That’s the question posed by biologists who have studied the heritability of intelligence in chimps.

It’s an interesting question. While we are relatively happy to accept that traits such as height and eye color come from our parents, it makes us uncomfortable to conclude that the same is true of intelligence. The role of genetics in animal intelligence has been even less fully investigated.

We are right to be uncomfortable about humans. Intelligence is a much more complicated trait than height, so it will be harder to find evidence that it has a heritable component. Even setting that aside, the idea that we are stuck with the cards we’ve been dealt at birth is a hard one to swallow. We like to think that we are all equal and we get where we are through hard work.

There’s another issue: The most commonly used test for intelligence, IQ, is itself rife with problems.

And there are still worse taboos. If we were to allow that intelligence was genetic, the very real fear is that some people would start arguing that (say) men are smarter than women, or that some races are intellectually superior to others. It is by no means an idle worry. The former president of Harvard University had to resign in 2006 after saying that there weren’t enough high-IQ women around. And a book in the 1990s, “The Bell Curve,” generated huge controversy with its linkage of racial groups and intelligence.

Going back further, the examples become worse. In the late 19th century, Charles Darwin’s cousin Francis Galton founded the Eugenics Education Society. Believing that intelligence was strongly genetically determined, he suggested that genetically “superior” people should be allowed to have children, while “inferior” people should be sterilized. The idea did huge damage, catching on in the United States, where thousands of people were sterilized, and in Germany, where it was embraced by the Nazis.

So you can see why evidence that there is indeed a genetic component to intelligence has been viewed with suspicion.

Many studies, and in particular comparisons of identical and nonidentical twins raised together and raised apart, have found that there is a strongly heritable component to intelligence. IQ turns out to be about 50 percent heritable. This means that half of the differences in intelligence between different people can be put down to genetic factors. For height, the proportion is 90 percent.

This view seems to have percolated down into general knowledge. Most people would take the common-sense view that if you have clever parents, you’re already on the road to being clever yourself, but also that the opportunities you get during your childhood and youth will go a long way to influencing how smart you become.

It turns out that a similar proportion of chimp intelligence is now known to be heritable.

The last time I spoke with Tetsuro Matsuzawa — the renowned head of the Primate Research Institute at Kyoto University — he emphasized how smart chimps are. “We underestimate chimpanzee intelligence,” he said.

Now a new paper demonstrates what Matsuzawa knows to be true from his close work with wild and captive chimps: Some are smarter than others.

William Hopkins, of Yerkes National Primate Research Center in Atlanta, and colleagues studied 99 captive chimps (from age 9 to 54) and had them perform 13 different tasks.

Because the chimps’ backgrounds are known, the researchers are able to account for genetics and the environment in which each animal was raised, and so are able to separate out the proportion of ability that is down to genetics. They found that about 50 percent of the variation in chimp ability is down to their genes. (The results are in the journal Current Biology, DOI reference 10.1016/j.cub.2014.05.076.)

“As is the case in humans, genes matter when it comes to cognitive abilities in chimpanzees,” says Hopkins. “It doesn’t mean that they are the only factor determining cognitive abilities, but they cannot be ignored.”

Another interesting spinoff of this research is that it could illuminate our understanding of human intelligence. In chimps we don’t have to worry about what socioeconomic background they came from, or which school they attended. Eventually, the Yerkes team says, the work may uncover particular genes that are related to intelligence.

This is an intensely debated subject. So far, no genes have been definitively linked to intelligence. (There have, on the other hand, been genes linked to adult weight and, of course, to many different genetic diseases.) Even the thought of it is enough to make people invoke “Brave New World” and “Gattaca” — fictional explorations of societies where people are stratified according to their genes.

I spoke to Matsuzawa again this week, and he is not surprised by the Yerkes results. “Genetic and environmental factors both must be important,” he says. “The question is, how?” Matsuzawa says his team have sequenced the genome of one of their “prodigy” chimps, Ayumu, and that of Ayumu’s super-smart mother, Ai, and his father, Akira. “You can see what is inherited from the father and what is from the mother,” says Matsuzawa. “That’s exciting.”

Hopkins says, “What specific genes underlie the observed individual differences in cognition is not clear, but pursuing this question may lead to candidate genes that changed in human evolution and allowed for the emergence of some human-specific specializations in cognition.” He stops short of suggesting that we might actually find genes underlying differences in human intelligence.

But candidate genes will no doubt be found. And then we can expect an intense burst of controversy and soul-searching.

Rowan Hooper (@rowhoop on Twitter) is the news editor of New Scientist magazine. The second volume of Natural Selections columns translated into Japanese is published by Shinchosha at ¥1,500. The title is “Hito wa Ima mo Shinka Shiteru (The Evolving Human).”