How strong is a chimpanzee, really?

Friday, February 27th, 2009

I’ve been asking, How strong is a chimpanzee, really?, and John Hawks of Slate has done the research to answer that question — rather than repeat the same factoids going around:

After last week’s chimpanzee attack in Connecticut, in which an animal named Travis tore off the face of a middle-aged woman, primate experts interviewed by the media repeated an old statistic: Chimpanzees are five to eight times stronger than people. The literature — or at least 19th-century literature — concurs: Edgar Allan Poe’s fictional orangutan was able to hurl bodies and pull off scalps. Edgar Rice Burroughs’ fictional anthropoid apes were likewise possessed of remarkable strength. Even Jules Verne’s gentle ape, Jupiter, had the muscle to drag a stuck wagon from the mire.

In 1923 biologist John Bauman decided that a scalp-pulling orangutan was grotesquely impossible, so he decided to test the strength of actual apes at the Bronx Zoo with a dynamometer. The apes didn’t generally cooperate, but one chimp managed to pull 1,260 pounds. Later, the largest chimpanzee then in captivity, named Boma, pulled 847 pounds one-handed. This was more than the “husky lads” on his South Dakota football team could pull — 200 pounds with one hand, 500 with two.

This is the number that entered the anthropology textbooks and the talking points of primatologists like Jane Goodall and Sue Savage-Rumbaugh.

But the “five times” figure was refuted 20 years after Bauman’s experiments:

In 1943, Glen Finch of the Yale primate laboratory rigged an apparatus to test the arm strength of eight captive chimpanzees. An adult male chimp, he found, pulled about the same weight as an adult man. Once he’d corrected the measurement for their smaller body sizes, chimpanzees did turn out to be stronger than humans — but not by a factor of five or anything close to it.

Repeated tests in the 1960s confirmed this basic picture. A chimpanzee had, pound for pound, as much as twice the strength of a human when it came to pulling weights. The apes beat us in leg strength, too, despite our reliance on our legs for locomotion. A 2006 study found that bonobos can jump one-third higher than top-level human athletes, and bonobo legs generate as much force as humans nearly two times heavier.

Still impressive.

Chimps have proportionally more arm muscle than humans, but their muscles tend to be stronger in general, because chimps have the “strong” form of the ACTN3 gene — like Jamaican sprinters — and thus have more “fast twitch” muscle fibers.

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