According to this piece in the Smithsonian, the human chin is unique to homo sapiens and isn’t found in other hominid species (I didn’t know this). So what’s the purpose of the chin in humans?
Perhaps the most common explanation is that our chin helps buttress the jaw against certain mechanical stresses. Ionut Ichim, a Ph.D. student at the University of Otago in New Zealand, and colleagues suggested in the journal Medical Hypotheses in 2007 that the chin evolved in response to our unique form of speech, perhaps protecting the jaw against stresses produced by the contraction of certain tongue muscles. Others think the chin evolved to safeguard the jaw against forces generated by chewing food. Last year, Flora Gröning, a biological anthropologist at the University of York in England, and colleagues tested the idea by modeling how modern human and Neanderthal jaws withstand structural loads. Their results, which they reported in the American Journal of Physical Anthropology, indicated the chin does help support the jaw during chewing. They suggested the chin may have evolved to maintain the jaw’s resistance to loads as our ancestors’ teeth, jaws and chewing muscles got smaller early on in our species’ history.
A completely different line of reasoning points to sexual selection as the driver of the evolution of the chin. Under sexual selection, certain traits evolve because they are attractive to the opposite sex. Psychological research suggests chin shape may be a physical signal of the quality of a mate. For example, women may prefer men with broad chins because it’s sign that a man has good genes; likewise, a woman’s narrow chin may correlate with high levels of estrogen…
(hat tip: Tyler Cowen)