Scientists--of a certain sort, anyway--have finally figured out why human beings have such large brains compared to other mammals: we started having smaller jaws and it is this to which we owe both our big brains and sophisticated culture. This single genetic mutation that weakened our jaw muscles happened about 2.4 million years ago, a new study suggests.

"Over the past 2.5 million years, human brains have grown enormous compared to those of other primates. Human brains are now roughly three times the size of those of chimps or gorillas.

One possible reason is that changes in the environment forced early humans to invent tools, and those with the biggest brains had greatest manual dexterity, which led to yet more sophisticated tool use. Alternatively, selection may have favoured larger brains because they permitted more complex cultures.

But why did this process occur in humans and not in other primates? According to Hansell Stedman, an expert on muscle disorders at the University of Pennsylvania in Philadelphia, it was a simple mutation in a gene found in our jaw muscles." Isn’t this fun?