Dashiell Hammett mentioned Sam Spade’s jutting chin in the opening sentence of his novel, “The Maltese Falcon.” Spade’s chin was among the facial features Hammett used to describe his fictional detective’s appearance, but starting with that distinctive chin was—at least from an evolutionary perspective—an unintentional redundancy, since every chin is distinctive in the sense that humans are the only primates to possess that physical characteristic.
Chimpanzees, humans’ closest living relatives, do not have a chin. Neither did Neanderthals, Denisovans, or any other extinct human species. Humans, it turns out, have a unique capacity to “take it on the chin” because we’re uniquely in possession of that physical feature. That exclusive nature makes the chin well suited for identifying Homo sapiens in the fossil record.
In simplest terms, a chin is a bony projection of the lower jaw. So why is it there? How and why did it evolve?
