You Asked
Why are chimps so much stronger than humans? — Grafton, Pittsburgh, Pa.

Marshall Answered
It is true that chimps (and other primates) are stronger than human beings. For example, this article points out that, gram for gram, the muscle of a bonobo is twice as strong as a human muscle. This article discusses several displays of chimp strength that put humans to shame.

What could cause the strength difference? It’s not completely clear, but here is one thing we know. There is a gene called MYH16 in both humans and other primates. In humans, this gene is damaged. This makes human jaw muscle fibers one third the size of chimp muscle fibers. It’s a fascinating thing, because this mutation may have made the larger brains of humans possible, as described here:

It is likely that this gene, or the same kind of mutation in another gene, is affecting the strength of human muscles.