Why we have chins | Hacker News Reader

Why we have chins

sciencedaily.com

27 pointsdiodorus31 comments

Aside from the chin...look at the picture of the modern human skull compared to the Neandethal-era skull. Notice Neandethal-era skull has a perfect bite and the modern human skull has an overbite. The overbite is the direct result of humans developing/using eating utensils (this fact may have actually been from a recent HN front page post).

The overbite-utensil hypothesis is interesting. But why do overbites exist in modern human societies that eat almost entirely with their hands?

In hindsight, I really didn't mean to emphatically state:

"The overbite is the direct result of humans developing/using eating utensils"

I just meant to mention the theory and that I thought I first learned about the theory on the HN front page, but perhaps I read about it elsewhere anyway.

Looking just quickly at Google I believe the theory originates with Anthropologist, C. Loring Brace [1] a specialist in the evolution of hominid teeth[2].

[1]http://en.wikipedia.org/wiki/C._Loring_Brace [2]http://benedante.blogspot.com/2013/03/overbites-and-history-...

Can't get over how Lamarckian this sounds. How long have we been eating with utensils? Long enough for such a radical change? And is an overbite really such a disadvantage that it would select you right out of the gene pool?

Human physical genetic changes have accelerated in the last 50,000 years. Probably accompanying new pressures brought by living in social groups. But since the fork was only invented 400 years ago, maybe utensils is a reach.

Surely "utensils" includes more than just modern style metal forks? I don't think it's a stretch to say that the use of tools of any kind in the eating process could remove specific evolutionary pressures that would otherwise inhibit some individuals from reproducing.

I think it is a developmental rather than an evolutional effect.

Here's the presumable popularization of the idea:

https://books.google.com/books?id=5_EyCAAAQBAJ&lpg=PT76&ots=...

Which was then mentioned in the Atlantic:

http://www.theatlantic.com/health/archive/2013/01/how-forks-...

I don't get this statement, and it goes against my understanding of evolutionary forces.

Of the 5 evolutionary forces that I am aware of, founder effects, genetic drift, mutation, migration and selection, only one "responds" to the environment (selection). To respond to an event such as the invention of eating utensils, selection would dictate that a particular trait would have to give a survival/mating advantage over not having it.

It is suggested that those with an overbite we able to survive/mate better in the presence utensils than those without an overbite?

I know nothing about biology, but how about this:

The evolutionary path was influenced via selection. Those who made and used tools were more likely to survive/mate successfully, and those who made and used tools also tended to use them as eating utensils, which mechanically leads to an overbite. So eating with a fork doesn't directly lead to being selected for survival, but it's likely if you eat with utensils you also use other tools for things like hunting, defence, etc. and that does lead to increased survival.

It doesn't work like that.

That type of association is called "Lamarckian" after Jean-Baptiste Lamarck who posited that animals can "pass on characteristics that it acquired during its lifetime to its offspring"[1]. But animals do not pass on traits they acquired during their lifetime via genetics.

So even if utensils over one's life caused a overbite, it would not be transmitted via genetics to one's offspring. In order for evolution and utensils to interact via selection, it would have to be the case in which there was a genetic trait associated with an overbite that made you more fit when using utensils than those without it, thus out-mating the competition.

[1]http://en.wikipedia.org/wiki/Lamarckism

Why can't the opposite be true; those without an overbite are able to survive/mate better in the absence of utensils? Then the modern presence of overbite is easily explained as genetic drift.

I would guess that many modern mutations could be explained this way -- human invention alleviates evolutionary pressure keeping historically negative traits from flourishing.

It's surprising just how recent it was, too -- Richard III's skull, for example, clearly demonstrates the "perfect bite", and he lived just a bit more than 500 years ago.

https://www.google.com/search?q=king+richard+iii+skull&tbm=i...

First thing that came to my mind is that chins might be better as attachment for facial muscles giving more expressive or efficient face expressions or talking.

My first thought was that a chin may take a punch better...

But protruding chins don't really take punches that well, do they? The prototypical knockout punch is one that suddenly knocks the chin to the side, rotating the skull more quickly than the brain, bruising the brain both when the skull makes contact and when the brain passes the skull and makes contact on the other side.

Punching is the reason we have flat faces. They turned up around the same time we learned how to make fists. There was a research about that recently.

This article claims that chins handle stress worse not better (although I'm not sure if they meant stress associated with chewing or getting hit).

Quite the opposite. A punch on the chin will knock you out easily.

Not to argue, but is being knocked out bad? It seems like a common occurrence to a fight is go to unconscious. Some people have strong chins. Would they do better in a no rules fight historically, if they didn't go down?

Getting knocked out in an athletic competition is one thing. Getting knocked out when a neighboring tribe is attempting to kill all your men and old folks, enslave everyone else, and steal everything of value, would probably have been something else.

If you're unconscious, you're not a threat any more.

Live to fight another day.

Inter-tribal resource wars might be fought by primitives, but they're not fought by idiots. Nor are they fought by chivalrous knights. The throats of unconscious warriors will be cut. Even if a throat was missed in all the chaos, what is the evolutionary advantage to a male of living on after all fertile females have been abducted?

"Our study suggests that chin prominence is unrelated to function," Holton says, "and probably has more to do with spatial dynamics during development."

Just as a sidenote on this theme, it's interesting how according to studies chin prominence correlates with perceptions of leadership ability, confidence and sexual attractiveness in men. Apparently chin implants are as popular as breast augmentations these days:

http://www.reuters.com/article/2012/05/03/us-chinimplants-id...

Here's a link to the original article ("The ontogeny of the chin: an analysis of allometric and biomechanical scaling"):

http://onlinelibrary.wiley.com/doi/10.1111/joa.12307/full

Would like to point out that we're not the only species with chins.

Elephants have chins, too. [1]

(This is my favorite fact at parties. I'm a blast.)

1. http://en.wikipedia.org/wiki/Chin

Do elephants have a chin since they use their trunk as an eating utensil?

My instinct is to see chins as shields to the Adam's apple. I have no explanation for why primates have less prominent chins, though.

How about chicks dig guys with a manly chin.

Don't know how you can call yourself an evolutionary biologist if you so easily overlook sexual selection.

Because you need to ask why they dig a manly chin.

Long hair makes sense because it is a crude history of our health. Symmetry also makes sense, as it is a sign of healthy, strong genes. Being rich enough to afford to waste stuff also makes sense (and explain a ton of weird human and animal behavior)

But if a chin serves no purpose what so ever, why would it become a sex symbol? They're not big enough to work like antlers (look how much energy I can accrue to grow these big ass antlers!) so why would they start to grow in the first place?

It is unclear whether sexual selection impedes or facilitates natural selection [1]. Sexual selection can happen just because. A female who prefers chins will give birth to sons with chins and daughters who like chins. It's a positive feedback loop that doesn't need cooperation from natural selection to give it fitness.

At one time in the past there may have been a reason that the men with chins were more successful than other humans. The correlation may have been coincidental though. Maybe the men with no-chins happened to be living in a part of the world that suffered a famine. Or if there was a direct relationship, the sexual preference remained after the natural advantage was no longer relevant.

The study does a good eliminating mechanical advantage as a reason for having a jaw. (And that's all it says.) But the speculation about why the jaw exists (inserted by the news writer and has nothing to do with this study) seems less certain to me. Why did chins not simply get smaller with the rest of the skull? Something encouraged chin growth in humans. But to say what you'd have to study skulls from the past to see exactly how the chin changed over time.

[1] http://www.cell.com/current-biology/abstract/S0960-9822%2811...

Having a large / strong jaw and chin is correlated with higher testosterone levels and is a secondary sexual characteristic in males. Higher testosterone levels are correlated with a weakened immune response.

So yes, a "manly chin" may very well have been selected for on the basis of showing the strength of the individual by artificially handicapping them (being genetically "rich enough" as you put it).

Interestingly, beards act to further emphasize the chin. And we're one of the few animals to have those, too.

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