The chin. Now that’s something we don’t spend much time on nowadays. Unless they are unusual, they go largely unnoticed. And yet, human chins are unusual –all of them. In fact, according to a delightful article in the BBC : http://www.bbc.com/earth/story/20160204-why-do-humans-have-chins?ocid=ww.social.link.email ) we are the only primates –including our extinct relatives- who have chins. ‘[…] our chin is the protrusion of the bone that appears below the front wall of the human mandible (lower jaw). […] chimpanzee and ape jaws slant inwards for instance. Even our closest extinct relatives such as Neanderthals did not have them.’ Nobody seems to know why, though. Various theories have been proposed, but none of them would seem to be adequate explanations. For example, ‘[…] it has long been proposed that our chin may help us chew food. The theory goes that we need the extra bone to deal with the stresses involved with chewing.’ But, ‘If we were to protect ourselves from the stresses of chewing we would need more bone on the inner wall of the jaw near the tongue, not beneath our jaw.’ –that’s what you see in chimpanzees and macaques. And anyway, ‘says James Pampush of Duke University in Durham, North Carolina, who has been studying our humble chin for several years, we don’t have a very tough time chewing in the first place. Much of the food we eat is soft, especially cooked food. “That’s why the chin is not an adaptation for chewing”’.
Okay, what other function could it serve, because it does seem to have weathered the rigours of evolution? Well, it has been argued that ‘[…] our chin helps us to speak, that our tongue needs reinforcements from extra bone below our jaw. We are the primates with the most extensive speech repertoire.’ But speech doesn’t seem to justify the need for a chin: ‘[…] we don’t need much force to speak, so it’s not at all obvious why we would need extra bone to help with the process. And if we did need any extra bone, just like for chewing it would be far more useful to add it to the inside of our jaw, closer to our tongue, rather than tagging it onto the bottom of our jaw.’
A third idea is that ‘the chin doesn’t have an immediate function, but that it has been chosen by sexual selection. It is our equivalent of large-flanged orangutan faces or a male elk’s large antlers.’ The only problem with that answer is that it is a feature found in both sexes in humans… Who is selecting whom?
So, if it doesn’t seem to serve a purpose, why has it been preserved? The article suggests the chin may be a spandrel -a ‘”non-adaptive trait” that arises as a by-product of something else.’ This is a concept proposed by, among others, Stephen Jay Gould. A spandrel is ‘the name given to an architectural feature below some church domes that is often so ornate it looks as if it was the starting point for the building’s design. In reality, spandrels only exist because they help support the dome above them. In other words, spandrels – both biological and architectural – are a by-product of a change happening elsewhere.’ They are almost-exapts –our faces are apparently shrinking, so the spandrel has become more obvious…
I suppose, but the answer seems a bit of a reach, don’t you think? Sometimes I wonder about our need to explain everything… And then I cave in and realize I can’t resist either, and find myself scanning crowds for chins. Their variety is truly astounding when you actually look. Inevitably, I hearken back to first year medical school when we learned about the ‘gnathias’ (from Greek gnathos –jaw): too big, or too small. And then that always reminds me of the story of the Three Bears with baby bear’s stuff being ‘just right’…
And why that story in particular? Well, because apart from the hands, the face is the most likely part to be involved in intimacy. So, I wondered, would different chin sizes have any effects on, say, dating behaviour? I know my braces did when my parents decided my teeth weren’t perfect -I became a liability in the dark. Had my chin been longer, or as unpredictable as the metal on my teeth, would I ever have been able to negotiate anything other than a goodnight handshake? The issue, I realized, had existential overtones.
I needed to subject the matter to scientific scrutiny. At first, I thought perhaps I could do an online survey, but I realized that the type of people who responded might feel the need to exaggerate their own chin prowess –sort of a variation on the Napoleon syndrome- which would muddy the waters. And anyway a chin is a personal thing, like nostrils or Dumbo ears, so any imagined offence to any of them, real or imagined, would be a threat to the owner. I didn’t want to be the unwitting victim of hate blogs, or some vigilante group assembled with the express purpose of ridding the net-waves of people like me. And then, of course, there was Fake News to contend with.
I decided to do an eye-contact survey on my friends. Unfortunately, not only do I not have a large cadre of friends, but the only one I have did not strike me as particularly gnathically challenged. Brien was perhaps corporeally overly abundant and had a penchant for porches, but otherwise wasn’t unduly compromised by his chins. I use the plural because when he held his head just right, he seemed to have two of them. As a matter of fact I’m sure I counted three one time. So, I figured he would be like interviewing three chins and maybe I could extrapolate the results a little better on a graph.
I stopped on the sidewalk that led to his porch to see if he was awake. He’s always grumpy if I wake him up. Sometimes you can’t tell with Brien until you get really close, though, so it was a Sophie’s choice.
“Careful with that second concrete slab,” I heard a voice warn me. “The pizza guy won’t come any closer… It’s my guard slab, eh?” he added with a grin. But Brien knew I knew, so I could tell he was in a good mood. I could feel his eyes following me like a CCTV, though –he is very possessive of his porch, even with me.
I picked up one of the beers at his feet and sat on the only other chair beside him. As I stooped to pick it up, I tried to memorize his top chin. Interestingly, he had something I’d never noticed before: a chin pit –well, that’s what one of my Iranian classmates called it; it’s really a sort of dimple, a cleft chin, actually. It is a recessive gene of variable penetrance -meaning there is often a variation in how it appears. The only other thing I could remember from that class so long ago, was that it was considered a sign of beauty in Persia and the term ‘chin pit’ –or ‘chin well’- my classmate informed me, was so named because a lover might fall into it and become trapped.
I felt I was in no danger of that, but my eyes must have lingered a little too long on the area and Brien noticed. “Admiring my face?” he said and smiled good-naturedly.
Damn! You can’t get away with anything with Brien.
“My mother used to show her friends my chin, you know. She was quite proud of it –apparently I was the only one in the family with anything like it.” He quietly walked his eyes over to my face to see if I thought he was being vain. “Uhmm, the upper chin,” he snorted, almost too quickly. “I only had one in those days.”
Great, I thought, maybe some lover had swooned and fallen in. There was a chin story there -I could feel it. “Did…” I hesitated, trying to think of a neutral way to ask that wouldn’t make him decide to exaggerate.
“Did it affect my dating behaviour, you were going to ask?”
Now how would he know that? I shrugged, as if I wasn’t -but that if he was going to tell me anyway, I’d listen.
He smiled, and took a long sip from his beer. “Nope…” He took another sip and finished off the can. “My mother thought so, though,” he continued after opening yet another one. “She said that having one of these…” he added, pointing to the chin dimple, “…would get me into no end of trouble.”
“And did it…?” Perhaps I was too quick to question him because he just winked and shook his head.
“What’s past is past, eh?” he said and sent his eyes to scout out any changes in Sheda, his pet cedar tree at the far end of the yard. “And anyway, I only needed to take the medicine for two weeks…”
I nodded; chins can certainly be a problem.