It took a bit long to get to a spandrel explanation, but once it did, it was thorough. As an observation, https://en.wikipedia.org/wiki/Chin https://en.wikiped

It took a bit long to get to a spandrel explanation, but once it did, it was thorough. As an observation, https://en.wikipedia.org/wiki/Chin https://en.wikipedia.org/wiki/Chin quotes: > Enlow, Donald H. (1982). Handbook of facial growth. Philadelphia: Saunders. p. 283. ISBN 0721633862. "In the human mandible, a prominent chin marks this region, a distinctive feature that characterizes the face of modern man (and also, for reasons yet to be studied, the elephant)." and further qualifies "although this leads to debate over the use of the term." The Atlantic author does a followup on this topic, at http://www.theatlantic.com/notes/2016/01/no-really-other-animals-dont-have-chins/433890/ http://www.theatlantic.com/notes/2016/01/no-really-other-ani... , saying: > “For these reasons, it is generally agreed that whatever the biological situation occurring on the front of the elephant lower jaw, it is fundamentally different from the condition in humans,” says James Pampush, who recently reviewed the various possible origin stories for the human chin. “It may provide some insights into the situation in humans, but to call it a 'chin' stretches the definition.” However, that addresses a different topic. In common speech we use "hair" to refer to refer to hair on a mammal, made primarily of keratin, and to a chitinous seta on an insect. Thus, "hair" does not depend on a shared evolutionary history, though I think Pampush would prefer that to be the case. If that were the case then "chin" would, by definition, only apply to humans.