
We're the Only Animals with Chins - henrik_w
http://www.theatlantic.com/science/archive/2016/01/were-the-only-animals-with-chins-and-no-one-knows-why/431625/?single_page=true
======
lawpoop
I posted this on reddit last night:

Any time there's a special feature on a bone, usually a muscle attaches to it.
I googled, and found out that the mentalis muscle attaches to the chin.

Interestingly, wikipedia says "In conjunction with orbicularis contraction,
the mentalis muscle allows the lips to 'pout.' Externally, mentalis
contraction causes wrinkling of the chin skin, as used in expressions of doubt
or displeasure. It is sometimes referred to as the 'pouting muscle.'"
[Emphasis mine]

Humans have complex facial expressions, and I would say that the pout is part
of the repertoire. When someone is pouting, they are in extreme emotional
distress, on the verge of sobbing. Having such an obvious "tell" would be
beneficial to a social species, probably leading to conciliatory behavior and
promoting de-escalation and group cohesion during conflict.

I did some cursory googling to see of the mentalis is involved in speech
production, but found nothing at my level. Offhand I can't think of any
particular speech sounds I can make when my lips are in pout formation.

~~~
petke
Chimps pout better than any selfie teen. So I don't think that's it

~~~
lawpoop
Can you post a picture? I did a google image search, but didn't find any
pouting chimps.

They do purse their lips, but that's a different set of muscles.

------
dalke
It took a bit long to get to a spandrel explanation, but once it did, it was
thorough.

As an observation,
[https://en.wikipedia.org/wiki/Chin](https://en.wikipedia.org/wiki/Chin)
quotes:

> Enlow, Donald H. (1982). Handbook of facial growth. Philadelphia: Saunders.
> p. 283. ISBN 0721633862. "In the human mandible, a prominent chin marks this
> region, a distinctive feature that characterizes the face of modern man (and
> also, for reasons yet to be studied, the elephant)."

and further qualifies "although this leads to debate over the use of the
term."

The Atlantic author does a followup on this topic, at
[http://www.theatlantic.com/notes/2016/01/no-really-other-
ani...](http://www.theatlantic.com/notes/2016/01/no-really-other-animals-dont-
have-chins/433890/) , saying:

> “For these reasons, it is generally agreed that whatever the biological
> situation occurring on the front of the elephant lower jaw, it is
> fundamentally different from the condition in humans,” says James Pampush,
> who recently reviewed the various possible origin stories for the human
> chin. “It may provide some insights into the situation in humans, but to
> call it a 'chin' stretches the definition.”

However, that addresses a different topic. In common speech we use "hair" to
refer to refer to hair on a mammal, made primarily of keratin, and to a
chitinous seta on an insect. Thus, "hair" does not depend on a shared
evolutionary history, though I think Pampush would prefer that to be the case.

If that were the case then "chin" would, by definition, only apply to humans.

~~~
pierrec
It's an interesting interpretation, but I don't think Pampush is arguing that
a trait must be present in a common ancestor in order to have a single name.
He's certainly familiar with parallel evolution, usually the basic examples
given are the bat's wings and cephalopod's eyes, maybe even more striking than
the insect hair example.

He says it's fundamentally different, and I think I can see how that's the
case, seeing how elephants can actually close their mouth/trunk onto their
chin (giving it an obvious use), and also considering the structural
difference where the elephant's chin is a direct continuation of the line
where teeth are resting. It's more of an extended lower jaw than a separate
protuberance like in humans. That being said, I'll keep on calling it a chin.

~~~
dalke
You're right. I misread that. Upon reconsideration, I think it's the author
interpreting Pampush that way.

------
3455434687
If the fist evolved to punch: [http://www.latimes.com/science/sciencenow/la-
sci-sn-human-fi...](http://www.latimes.com/science/sciencenow/la-sci-sn-human-
fist-punching-evolution-males--20151021-story.html) ...it's maybe conceivable
that the chin evolved to resist chokes? Choking can be very effective, and
tucking your chin is an important defense:
[http://www.grapplearts.com/finishing-the-rear-naked-
choke/](http://www.grapplearts.com/finishing-the-rear-naked-choke/)

~~~
petke
The chin just helps people choke you better. You cant slip out of their grip
as easy. Also a big chin is bad for fighting. The easiest way to knock someone
out I to hit them on the chin. It makes the head turn and the brain bounce
against the skull. The more the chin sticks out the easier it is to hit and
the more the head turns.

~~~
3455434687
"The chin just helps people choke you better." I'm no expert, but I've
grappled a lot, and this hasn't been my experience. It's also inconsistent
with my second link. Are you speaking from experience, can you support with
citation, or are you speculating? I'm happy to be educated, if you can back
this up.

~~~
petke
I'm no expert just an mma fan. The rear naked choke for instance. Once they
get under your chin its hard to slip out. The bigger the chin the more
difficult. The chin is like a hook. Imagine a person without a chin. He could
just pull his head out. Especially if they are sweaty.

~~~
3455434687
I see what you mean. I agree, "once they get under your chin, it's hard to
slip out" \- I also agree that "he could just pull his head out" \- but in
both cases, only if the head/neck grip is the primary grip, and there's no
leg/body control.

In my experience, leg and body control make or break a RNC, not head/neck
grip:
[https://en.wikipedia.org/wiki/Rear_naked_choke#.22Body_Lock_...](https://en.wikipedia.org/wiki/Rear_naked_choke#.22Body_Lock_or_Hooks.22_variation)
. It's way easier to escape a RNC that neglects leg/body control whether or
not they've passed the chin:
[https://www.youtube.com/watch?v=JR2e0IsqhrQ](https://www.youtube.com/watch?v=JR2e0IsqhrQ)
, and the chin is an important part of the last-ditch defense.

...which is a long way of saying, I'd rather fight a dude with no chin, and if
there were some option to temporarily remove my chin while grappling, I'd
still decline, for performance reasons :)

I'd love it if a more experienced MMA player could chime in to confirm or deny
our suspicions.

------
yes_or_gnome
Seems like everyone that is suggesting reasons why humans evolved chins didn't
read the article. So, here's a NPR interview, with transcript, for them to
ignore too.

[http://www.npr.org/2016/01/29/464893281/why-do-humans-
have-c...](http://www.npr.org/2016/01/29/464893281/why-do-humans-have-chins-a-
scientist-explains-the-enduring-puzzle)

In short. It's unlikely to be for protection, or for sexual selection, or to
aid in speech. Go to the interview detailed explanations.

~~~
bcook
Ouch. I suppose we _should_ read the articles... though, since there is no
obvious answer, let us have our conversation. The condescension was not
helpful.

Most of the comments here offer reasons that are even mentioned in the
articles as plausible.

------
nsns
But must an explanation always be a functional one? This seems extremely
limited and limiting. Certainly the shape of the body, like every complex
system, has some contingent or incidental characteristics to it (e.g. five
fingers, various eye colors, etc.). It also stands to reason that every animal
would have some unique manifestations of its differentiation from all others;
it would obviously be a fallacy to consider such differentiating traits as
necessarily important in and of themselves.

~~~
dalke
You are right - no, it doesn't. The article mentions Gould and Lewontin's
'spandrel' theory as one a framework to understand non-functional explanation,
then presents a spandrel explanation for the chin.

You might be interested in reading their original paper, "The Spandrels of San
Marco and the Panglossian Paradigm: A Critique of the Adaptationist
Programme", available from
[http://faculty.washington.edu/lynnhank/GouldLewontin.pdf](http://faculty.washington.edu/lynnhank/GouldLewontin.pdf)
.

------
bcook
Perhaps it is intended as structural protection of the mouth from the
inevitable fall that we bipeds experience.

Does any other animal fall as commonly & dangerously as humans?

~~~
Systemic33
That ought to make our noses smaller by the same logic.

~~~
bcook
Make the nose smaller to protect what? I do not see the logic.

I have fallen and busted my chin a few times, but never my nose. How about
yourself?

~~~
rimantas
make nose smaller to protect the very same nose.

~~~
lawpoop
Do people fall and bust their nose?

------
nonbel
Reminds me of the idea that at some point a pair of (relatively close in time)
genome duplications gave rise to jaws, adaptive immune systems, and a bunch of
neuropeptides:

"Nearly forty years ago, Susumu Ohno proposed that one or two rounds of whole
genome duplication took place close to the origin of vertebrates. The refined
version of this proposal, known as the two round (2R) hypothesis, assumes that
the genome of jawed vertebrates has been shaped by two rounds of whole genome
duplication that took place after the emergence of urochordates and before the
radiation of jawed vertebrates. [...] Of special interest in this connection
is the proposal of Olinski et al. [ 45••] that the four sets of MHC paralogons
and the four sets of neurotrophin paralogons were derived from a single
contiguous region on an invertebrate proto-chromosome (Figure 2).
Interestingly, two of the neurotrophin paralogons [46] are located on
12p11–p13 and 19q13–q14 that encode the NKC and LRC, respectively."
[http://www.ncbi.nlm.nih.gov/pubmed/17707623](http://www.ncbi.nlm.nih.gov/pubmed/17707623)

------
c3534l
It would appear to me that Tarsiers have a slight chin:

[http://www.skullsunlimited.com/userfiles/image/variants_larg...](http://www.skullsunlimited.com/userfiles/image/variants_large_4225.jpg)

It's true that it's part of a slope inwards towards the body, but in most
pictures I could find it looks like it is definitely the same sort of
phenomenon talked about in the article. At certain angles it's pretty
remarkably a chin: [https://boneclones.com/images/store-
product/product-1169-mai...](https://boneclones.com/images/store-
product/product-1169-main-original-1415041962.jpg)

To my untrained eye, looking through mammal skulls the slope of the chin/not-
chin area seems to have more to do with the angle of the teeth than anything.

Actually, even other primates like this Siamang seem to have something pretty
similar to human chins:
[http://www.store.dinosaurgeorge.com/images/Siamang%20Gibbon%...](http://www.store.dinosaurgeorge.com/images/Siamang%20Gibbon%20Skull.png)

------
robotcookies
Almost every mammal has a protruding mouth to help bite/feed. Humans are the
exception and pre-humans like australopithecus had very prominent mouths like
other mammals. It seems very likely that chins are remnants of having much
longer jaws which have recently (evolutionarily speaking) shrunken. Why do so
many people have crooked teeth and need to remove their wisdom teeth? To me,
it seems more than likely that is due to the same mouth shortening (or
whatever you call it). Teeth disappearing in coordination with shrinking jaws
did not happen so it's quite possible chins didn't either.

I know there is no proof of this. But we accept many things as true because it
seems very likely. I think chins fall into the same where the above
explanation should be accepted as probably true until proven otherwise. Other
explanations just don't seem nearly as plausible. Even the 'attractiveness'
argument doesn't seem compelling to me as you're talking about every society
on earth. Did every community of humans on every continent find chins
attractive? Not likely.

~~~
dalke
The shrunken jaw hypothesis was discussed towards the end of the piece:

> A different explanation portrays the chin as a bit of the jaw that got left
> behind while the rest shrunk back. As early humans started cooking and
> processing our food, we made fewer demands upon our teeth, which started
> shrinking as a result. They gradually retracted into the face, while the
> part of the lower jaw that held them did not (or, at least, did so more
> slowly). Hence: chin.

> Stephen Jay Gould and Richard Lewontin, who coined the concept of
> evolutionary spandrels, liked this hypothesis. So does Nathan Holton from
> the University of Iowa, who studies facial evolution. “It seems that the
> appearance of the chin itself is probably related to patterns of facial
> reduction in humans during the Pleistocene,” he says. “In this sense,
> understanding why faces became smaller is important to explaining why we
> have chins.”

> “But why did the lower border of the jaw also not shrink?” Pampush asks.

It then elaborates on the diversity of hypotheses:

> It may seem frustrating to have so many imperfect competing hypotheses, but
> that's part of the joy of chins: They reveal something about how scientists
> think about evolution. Some see the sculpting power of natural selection in
> everything, and view chins as surely some kind of adaptation. Others see
> natural selection as just one of many evolutionary forces, and so gravitate
> towards a spandrel-based explanation. “The chin is one of these rare
> phenomena in evolutionary biology that really exposes the deep philosophical
> differences between researchers in the field,” says Pampush.

~~~
robotcookies
I realize that it was discussed in the piece and never claimed it wasn't. My
claim is only that the argument is more likely than the other arguments (with
supporting bits about teeth added in).

~~~
dalke
My apologies.

------
mmanfrin
My uninformed guess of a thought has always been that the chin is shaped in a
way that helps protect the neck. When you tilt your head down, your jaw/chin
form a protective layer of skin and bone that surrounds the front half of your
neck (i.e. the side what would most likely be facing a threat/predator).

~~~
petke
If the neck was so vulnerable it needed protection why doesn't animals have a
chin. And why isn't there a permanent bone covering the neck at all times.

~~~
mmanfrin
Because of how we stand. We want to be able to reach/see higher, which means
stretching upwards. When you are lower/your chin angled down, there is near
continuous bone coverage, but when you are up/angled up, that area stretches.

Allows your head to pivot up and down from the hinge of the top of your spinal
column, but also allows for the front/variable length bit (the front of your
neck) to be protected when needed.

e: Expanding on this a bit, the only other animal that comes to mind that
stands like us that I can think of is the Meerkat. Why don't they have chins?
Maybe it's that they only stand in situations, not for movement; or maybe it's
that they aren't in situations where they can/have to fight back vs predators
(not that they don't have predators, but that human vs wolf is a bit more even
than meerkat vs lion, more of a chance for the human to prevail and more of a
chance for a human with the optional-neck-guard to eek out a win where a
chinless compatriot wouldn't).

------
strait
Oral sex advantage. Also as a general pleasure appendage. When your hands,
elbows, mouth, and even chest are all usefully employed simultaneously, the
chin may be the only thing you have left to use. Drag the chin up and down the
legs or chest with a sequence of short kisses for great effect.

------
jondubois
That's not true. Godzilla had quite a significant chin
[http://www.cinemablend.com/images/news_img/43084/godzilla_43...](http://www.cinemablend.com/images/news_img/43084/godzilla_43084.jpg)
;p

~~~
andrewflnr
That is interesting. Why would they put a feature like that on a city-
destroying monster? Did they know it was a distinctly human feature? Were they
trying to make a point about people destroying things? Or did they just think
it looked scarier that way?

------
jondubois
Actually I found an animal with a chin: Hemiramphus brasiliensis
[http://www.sosdom.lautre.net/Pages_Glossaire/AGlossImage_Fau...](http://www.sosdom.lautre.net/Pages_Glossaire/AGlossImage_Faune/Balaou.jpg)

------
colinramsay
I made a rather whimsical quiz on this topic:

[http://colinramsay.co.uk/chinorno/](http://colinramsay.co.uk/chinorno/)

Unfortunately you can never win, because the chimp question is a bit of a
stumper.

------
whybroke
>We're the Only Animals With Chins...

Is the author an Elephant?

------
jondubois
It's probably because of aesthetics. Humans are not birds; in our case, sexual
selection applies to both genders.

