John Hawks in Slate:
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.
Pulled scalps? Unstuck wagons? No doubt, chimpanzees are different from us. Their climbing lifestyle accentuates the need for arm strength. A chimp on four legs can easily outrun a world-class human sprinter. But it sounds extreme to suggest that humans are only an eighth as strong as chimpanzees. Consider that a large human can bench-press 250 pounds. If the “five to eight times” figure were true, that would make a large chimpanzee capable of bench-pressing 1 ton. It's just the sort of factoid the zoo staff might tell you to keep you from knocking on the glass.
The suspicious claim seems to have originated in a flapper-era study conducted by a biologist named John Bauman.