WE MAY owe our big brains and sophisticated culture to a single genetic mutation that weakened our jaw muscles about 2.4 million years ago. The slack muscles relaxed their hold on the human skull, giving the brain room to grow, a new study suggests. Meanwhile, other primates were stuck with stupendous jaw muscles that squeezed the skull tight.
Over the past 2.5 million years, the human brain has grown much bigger than those of other primates, and it is now roughly three times the size of chimp or gorilla brains. A possible reason is that environmental changes forced early humans…
