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chimpYou’ve been to the zoo, right? So surely you’ve seen a chimp sit on his haunches while looking with one eye and then the other, and again with one eye and then the other at something far away. He jumps to his feet. He starts to screech and hop menacingly. Then one arm starts whirling like a softball pitcher’s, except the chimp’s arm is circling in the wrong direction for underhand pitching. He does have something in his hand, and he’s preparing to throw it, hard. And then … the pitch! Woosh!

Ewww. He threw his feces. No. it’s never pleasant.

But when you are a researcher at the Yerkes National Primate Research Center of Emory University, you see a lot of this sort of thing. And it’s not always feces that chimps throw.

“Aimed throwing” is rare in any species except chimps and humans. Intrigued by why that might be, psychobiologist William Hopkins of the Yerkes Center observed that, often, its purpose seems to be to chase someone away. As a “go-away!” gesture, it’s a particularly effective form of communication.

And if it is primate communication, Hopkins reasoned, eons ago it might have been an evolutionary precursor to human speech.

Are chimps who have good aim also good communicators? And is the area of chimp brain that is analogous to the speech-controlling area of human brain (a/k/a the “Broca area”) especially developed in chimps with good aim? Hopkins decided to find out.

As reported in Philosophical Transactions of the British Royal Society B, Hopkins and a team of students tracked several years of throwing behavior in a group of chimps at Yerkes. The team learned that, just like humans, some chimps have really good aim. MRIs of those chimps’ brains showed Broca areas that were, indeed, anatomically unusual. They had significantly more white matter.

In brains, grey matter holds the nerve cells, while white matter holds the connectors extending to other brain areas. The abundance of white matter suggested to Hopkins that the Broca areas of well-aiming chimps were unusually well-connected.

As it turned out, the chimps with more white matter were also especially good at communicating by gesture with humans. They were, in general, sophisticated socially. At the same time, they proved no more intelligent than their peers on problem-solving tests.

At the Yerkes Center, humans hadn’t taught chimps to throw, or given rewards like bananas when a chimp hit a target. So it seemed probable to Hopkins that aimed throwing developed naturally in chimps and other primates, perhaps as an aid in hunting and defense from predators. If so, those who threw well may have had a survival advantage that got bred into progeny.

And the rest, as they say, would have been history. Millions of years later, the earliest anatomically modern humans were on the scene. Two hundred thousand years after that, a certain high-verbal human struck it big turning the “stuff”-related quips his father hurled into a best-selling book, and a TV series, too.

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