[blam]

"In a weird coincidence, I just learned last year that humans are the only primate that has a 'chin.' In fact, we're the only animal on the planet with a chin. There's not even a universally accepted theory on why our evolution produced chins. "

Sexual selection?

[ScubaDiver]

That’s one of the several hypothesis. Some think that as our faces shrank (other primates have much bigger faces relative to head size than humans do), perhaps the chin became a kind of plumage like birds will sometimes use to attract mates.

For the longest time, the prevailing opinion was that the chin developed to better help leverage chewing forces. But, a few years ago, that was largely debunked by researchers. Somehow, the were able to demonstrate the size of the chin had no bearing on bite force.

So, it’s either sexual selection, speech related or perhaps just an meaningless artifact of evolution.