Our preferences for chins may reveal their purpose

What separates humans from apes? Humans have tried to establish our distinction from other animals for thousands of years, claiming our everything from tool usage (nope) to temporal abstraction (sorry). The list of unique human traits has been getting winnowed down the more we learn about the world around us. But one critical trait has yet to be matched by our primate cousins: our chins.

No other primate has a chin like ours. This is undisputed, and no other primate species looks like they’re trying to knock humans off this pedestal any time soon. It’s just that, it’d be so much easier to proud of our chins if we were sure why we had them in the first place.

Many possible purposes for our facial protrusion

Many theories have been proposed. Does it help with speech, allowing attachment points for specialized muscle groups? Does the chin help absorb stress caused by our otherwise smaller jaws and teeth?  This was supported a bit by comparisons to Neanderthal jaws, but it ignores a key pattern in our chin-structures, and that’s the sexual dimorphism visible in most human faces.

The newest theory is based entirely around sexual selection as the motivation behind our current chins. Men generally have taller, more pronounced chins which may be read as a sign of good genetics to potential mates. Women then have narrower chins, possibly corresponding to having more estrogen. Proponents of this theory argue that if chins were needed for a universal, mechanical need like chewing, we’d all have the same chins, because… eating is pretty important. The fact that dimorphism exists indicates that jaw support is not the need driving these boney knobs at the bottom of our faces. And compared to the dimorphism in other parts of our bodies, or especially other species, a broader or narrower chin isn’t that big of a stretch.

Detractors, however, ask why chins couldn’t have started as jaw support, and branched off from there? Does any of this dimorphism go so far as to undo mechanical gains of having a chin? The timeline needs to be fleshed out further to see what came first— our bite, our speech or our dashing good looks.

Source: Why Do Humans Have Chins? by Erin Wayman, Smithsonian.com