Chin up!

An encouragement that can apply only to human

My 1950s comic hero “Nick Knatterton” of the weekly magazine “Quick” had a pointed and obviously very tough chin. Massive but rounder chins were the distinctive features of the Australian and New Zealand comic strip heroes Barry McKenzie and Wal Footrot, and even though Hervé’s “Tintin” did not have a prominent chin, he certainly had one, because it is a unique feature of all Homo sapiens, big and small. The chin, actually a bony protrusion medically often referred to as “the mental prominence”, is already noticeable in the foetus, but it becomes more and more obvious during the growth phase of a human after birth. No primate ancestor, no other mammal than the human species, has a chin and this continues to puzzle scientists representing different disciplines to this day.

A number of theories have been put forward to explain this peculiar feature of our anatomy. One holds that the chin helps us to articulate, in other words to speak and that our tongue’s movements need to be supported from the extra bone. Although humans are the only species in which speech plays a very important role in communication and the idea that the muscles to move the tongue need an additional support structure in the form of a chin, may initially sound plausible, there isn’t much force involved at all to move the tongue . And if an additional bony structure were indeed needed, why not in the jaw?

Another idea was that the chin somehow evolved as an aid to reduce stresses occurring during chewing. But we almost certainly chew much less than chimpanzees and gorillas (our closest animal relatives), and they do not have a chin. And what about the idea that the chin evolved as an adaptation for sexual selection? That also does not make much sense, because both men and women have a chin and sexually selected traits like antlers or manes are usually restricted to one sex only. Another suggestion has been that the chin was the consequence of the humans’ relatively small faces and that it compensated the reduced strength of the human jaw. Hormone levels would then have played a role as well. However, remembering how my hero “Nick Knatterton” occasionally used his pointed chin as a weapon, could it not have had a function in defence since our faces are flat, our teeth are small, and biting is difficult?

Or, could what I had observed many years ago provide an explanation? When I was a student many years ago, I had a girlfriend who had this habit of clamping a book or something between her chin and her chest, giving her two free hands to rummage about in her handbag searching for keys, a pen, or glasses. In other words, the chin could serve as a holding device leaving arms and hands free to be occupied with other things. No other mammal uses its hands as extensively as humans. On an excursion with boy scouts I also observed how the leader was carrying firewood in his arms right up to his chin, with the latter firmly securing the wood pile: the wood resting on his two outstretched arms, the chin clamping the pile from above. Although I have never come across this functional explanation for the presence of the chin, I think it’s not too outlandish a thought. Afterall, if a predominantly bipedal species that uses its arms to carry and transport “stuff” can use a method that increases the chance that none of the “stuff” falls down or gets lost, why not make use of the chin? Those able to carry more stuff like food or wood might have had a better survival chance and thus more offspring to pass on the “chinny trait”.

© Dr V.B. Meyer-Rochow and, 2021.
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