Why Do Humans Have Chins? A Scientist Explains The 'Enduring Puzzle'
ROBERT SIEGEL, HOST:
And now the question that has really been on your mind - why do humans have chins? Gorillas don't have them. Chimpanzees don't have them, nor do any of our other evolutionary relatives. In fact, with the arguable exceptions of elephants and manatees, humans are the only mammal with that little section of bone on the lower portion of the jaw that juts out past the teeth, and scientists don't know why. Well, James Pampush has co-authored a paper in the most recent issue of the journal Evolutionary Anthropology. The article is appropriately titled "The Enduring Puzzle Of The Human Chin," and he joins us now from the studios of Duke University to talk about it. Welcome to the program.
JAMES PAMPUSH: Thank you for having me.
SIEGEL: In this article, you round up quite a few possible theories that scientists have proposed, and then you seem to poke holes in each of them. So I wanted to start with the theory that this might be - the chin - might be an adaptation that helps us to speak. What's the idea there?
PAMPUSH: When you open your jaw and when the tongue moves, those muscles - they strain the front of the jaw. When bone is strained, it begins to accumulate small cracks. And so in order to deal with that, you want to add extra bone so that when the strains are put into it, it distributes more.
SIEGEL: You don't buy that.
PAMPUSH: I don't think that speech necessarily generates more strain there than other types of behaviors with the mouth that lots of other animals do without chins.
SIEGEL: One possible theory for why we have chins is that the chin can help humans attract mates.
PAMPUSH: Yeah. We run into another kind of interesting problem in that typically what happens when there's a feature that's being sexually selected in an organism, we see it develop in only one sex. So you might take the red cardinal as an example. We only see male cardinals that are red. And so it's really strange then that if chins are one of these features that is sexually selected for, that both men and women have chins.
SIEGEL: We do speak commonly of somebody taking it on the chin or leading with one's chin. Both of those phrases suggest that the chin is kind of a liability. But in each case, it does prevent you from getting hit in the throat, which would be a lot worse, so there could be some protective value of a chin.
PAMPUSH: Yeah, this is something that actually gets mentioned to me a lot.
SIEGEL: (Laughter) Yes. This bothers you a great deal (laughter).
PAMPUSH: Well, there's a couple of good reasons to suspect that that's not the reason that we have chins. First, human beings would have to be hitting each other so often or must be the clumsiest animals alive for as long as necessary to generate that kind of adaptation. And secondly, the chin is actually really bad in terms of preventing your jaw from breaking.
SIEGEL: The conclusion to your article - it sounds very profound. You say perhaps understanding the chin will reveal some unexpected insight into what it means to be human.
PAMPUSH: Well, if you're looking across all of the hominids, which is the family tree after the split with chimpanzees, there's not really that many traits that we can point to that we can say are exclusively human. Big brains - Neanderthals had larger brains than us. All those animals all walked on two legs. The one thing that really sticks out is the chin.
PAMPUSH: And perhaps it will tell us really what gave us that last little step into becoming atomically modern that left those other human-like creatures behind.
SIEGEL: Well, James Pampush, thank you very much for talking with us.
PAMPUSH: Well, thanks for having me.
SIEGEL: James Pampush is a postdoctoral associate at Duke University. His article in the journal, Evolutionary Anthropology is titled "The Enduring Puzzle Of The Human Chin."
(SOUNDBITE OF SONG, "CHIN UP")
DEBBIE REYNOLDS: (Singing) Chin up, chin up. Everybody loves a happy face. Transcript provided by NPR, Copyright NPR.