Why we have chins

http://www.sciencedaily.com/releases/2015/04/150413183745.htm

by diodorus • 11 years ago

27 31 11 years ago

diodorus• 11 years ago

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

randomname2• 11 years ago

"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...

will_brown2• 11 years ago

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).

juliangregorian• 11 years ago

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...

rpenm• 11 years ago

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

deeviant2• 11 years ago

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?

kyzyl• 11 years ago

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.

colanderman• 11 years ago

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.

nsxwolf• 11 years ago

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?

JoeAltmaier• 11 years ago

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.

nsajko• 11 years ago

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

maxerickson• 11 years ago

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-...

will_brown2• 11 years ago

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-...

scotty792• 11 years ago

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.

sheensleeves3• 11 years ago

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

jessaustin3• 11 years ago

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.

troels• 11 years ago

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

scotty792• 11 years ago

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).

whoopdedo2• 11 years ago

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.

wodenokoto• 11 years ago

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?

keithwhor2• 11 years ago

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.

whoopdedo2• 11 years ago

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...

dasmithii• 11 years ago

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.

keithwhor2• 11 years ago

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

ratsz• 11 years ago

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

Why we have chins

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