(Puny jaws have marked our lineage for as least 2 million years.) Many people have also lost another muscle-related gene called ACTN3. One gene, for example, called MYH16, contributes to the development of large jaw muscles in other apes. In the past few years, geneticists have identified the loci for some of these anatomical differences. A chimpanzee's skeletal muscle has longer fibers than the human equivalent and can generate twice the work output over a wider range of motion. But a more important factor seems to be the structure of the muscles themselves. How did we get to be the weaklings of the primate order? Our overall body architecture makes a difference: Even though chimpanzees weigh less than humans, more of their mass is concentrated in their powerful arms. But it is a fact that chimpanzees and other apes are stronger than humans. So the figures quoted by primate experts are a little exaggerated. 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. The apes beat us in leg strength, too, despite our reliance on our legs for locomotion. A chimpanzee had, pound for pound, as much as twice the strength of a human when it came to pulling weights. Repeated tests in the 1960s confirmed this basic picture. 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. An adult male chimp, he found, pulled about the same weight as an adult man.
In 1943, Glen Finch of the Yale primate laboratory rigged an apparatus to test the arm strength of eight captive chimpanzees. Number entered the anthropology textbooks and made its way into the talking points of recent primatologists like Jane Goodall and Sue Savage-Rumbaugh.īut the "five times" figure was refuted 20 years after Bauman's experiments.
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