8 ms·

We're the Only Animals with Chins

59 points by henrik_w 11y ago

dalke 11y ago
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-animals-dont-have-chins/433890/ http://www.theatlantic.com/notes/2016/01/no-really-other-ani... , 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 11y ago
  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 11y ago
    You're right. I misread that. Upon reconsideration, I think it's the author interpreting Pampush that way.
bnp272 11y ago
It's because we were designed to look like 'God."
- chippy 11y ago
  The why did 'God' have a chin?
  - swombat 11y ago
    So that he could stroke his chin wisely from above.
  - pram 11y ago
    because hes handsome
deleted 11y ago
[deleted]
bcook 11y ago
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 11y ago
  That ought to make our noses smaller by the same logic.
  - bcook 11y ago
    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 11y ago
      make nose smaller to protect the very same nose.
      - lawpoop 11y ago
        Do people fall and bust their nose?
- louprado 11y ago
  We're the only biped without a tail. Not sure how long arms compare to a tail for restoring balance but they are far better protection from falls compared to a chin.
3455434687 11y ago
If the fist evolved to punch: http://www.latimes.com/science/sciencenow/la-sci-sn-human-fist-punching-evolution-males--20151021-story.html http://www.latimes.com/science/sciencenow/la-sci-sn-human-fi... ...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 11y ago
  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 11y ago
    "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 11y ago
      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 11y ago
        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_or_Hooks.22_variation https://en.wikipedia.org/wiki/Rear_naked_choke#.22Body_Lock_... . 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 11y ago
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-chins-a-scientist-explains-the-enduring-puzzle http://www.npr.org/2016/01/29/464893281/why-do-humans-have-c... In short. It's unlikely to be for protection, or for sexual selection, or to aid in speech. Go to the interview detailed explanations.
- rquantz 11y ago
  It doesn't say it's unlikely to aid in speech, just that it's unlikely to be reinforcement for the stresses caused by the tongue while speaking.
- bcook 11y ago
  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.
- deleted 11y ago
  [deleted]
- vacri 11y ago
  "unlikey to be" is not "isn't". The counter to each of those items in the article is one researcher saying "yeah... I don't really think so", not something that's set in stone.
- ScottBurson 11y ago
  Well, here's what this article says about speech: Others have suggested that the chin is an adaptation for chinwags: It resists the forces we create when speaking. After all, speech is certainly a feature that separates us from other living animals. But there's no good evidence that the tongue exerts substantial enough forces to warrant a thick chunk of reinforcing bone. That's not my first thought at all. I think it has absolutely to do with speech, but not for that reason. I think it's to create more space for the tongue to move around and make different sounds. Just another SWAG, of course, but I'm surprised not to see this idea floated.
colinramsay 11y ago
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.
lawpoop 11y ago
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.
- rquantz 11y ago
  What an excellent idea. My first thought was that it must have something to do with speech or expression – maybe having a protruding bone bobbing up and down somehow makes speech more comprehensible? The idea of it contributing to facial expressions seem more likely though. Hopefully someone here will take up this line of inquiry.
  - dalke 11y ago
    The article mentions that hypothesis: > Others have suggested that the chin is an adaptation for chinwags: It resists the forces we create when speaking. After all, speech is certainly a feature that separates us from other living animals. But there's no good evidence that the tongue exerts substantial enough forces to warrant a thick chunk of reinforcing bone. “And any mammal that also communicates vocally or suckles or engages in complex feeding behaviors that involve the tongue are probably experiencing similar stresses and strains, and they're not getting chins,” says Pampush. Nor should we think that extra structure for complex sounds are needed for a language or comprehensibility. Consider the Silbo Gomero Language, which is "a whistled form of a dialect of Spanish." It "has only 2 vowels and 4 consonants, according to the official nomination document submitted during the UNESCO convention." (Quotes from Wikipedia.) Verbalized Morse code is another example of how simple vocalizations are all that are needed for a comprehensible language.
robotcookies 11y ago
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.
- deleted 11y ago
  [deleted]
- dalke 11y ago
  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.
whybroke 11y ago
>We're the Only Animals With Chins... Is the author an Elephant?
nsns 11y ago
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 11y ago
  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 .
jondubois 11y ago
That's not true. Godzilla had quite a significant chin http://www.cinemablend.com/images/news_img/43084/godzilla_43084.jpg http://www.cinemablend.com/images/news_img/43084/godzilla_43... ;p
- andrewflnr 11y ago
  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?
- bitwize 11y ago
  That's Zilla, not Godzilla.
c3534l 11y ago
It would appear to me that Tarsiers have a slight chin: http://www.skullsunlimited.com/userfiles/image/variants_large_4225.jpg http://www.skullsunlimited.com/userfiles/image/variants_larg... 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-main-original-1415041962.jpg https://boneclones.com/images/store-product/product-1169-mai... 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%20Skull.png http://www.store.dinosaurgeorge.com/images/Siamang%20Gibbon%...
mmanfrin 11y ago
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 11y ago
  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 11y ago
    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).
jondubois 11y ago
It's probably because of aesthetics. Humans are not birds; in our case, sexual selection applies to both genders.
nonbel 11y ago
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
strait 11y ago
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.
MonadQueen 11y ago
Some of us have more than one chin! http://openborders.info/wp-content/uploads/2099/12/paulgraham2.jpg http://openborders.info/wp-content/uploads/2099/12/paulgraha...
jondubois 11y ago
Actually I found an animal with a chin: Hemiramphus brasiliensis http://www.sosdom.lautre.net/Pages_Glossaire/AGlossImage_Faune/Balaou.jpg http://www.sosdom.lautre.net/Pages_Glossaire/AGlossImage_Fau...

59 points by henrik_w 11y ago

dalke 11y ago

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-animals-dont-have-chins/433890/ http://www.theatlantic.com/notes/2016/01/no-really-other-ani... , 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 11y ago
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 11y ago
  You're right. I misread that. Upon reconsideration, I think it's the author interpreting Pampush that way.

bnp272 11y ago

It's because we were designed to look like 'God."

chippy 11y ago
The why did 'God' have a chin?
- swombat 11y ago
  So that he could stroke his chin wisely from above.
- pram 11y ago
  because hes handsome

deleted 11y ago

[deleted]

bcook 11y ago

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 11y ago
That ought to make our noses smaller by the same logic.
- bcook 11y ago
  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 11y ago
    make nose smaller to protect the very same nose.
    - lawpoop 11y ago
      Do people fall and bust their nose?
louprado 11y ago
We're the only biped without a tail. Not sure how long arms compare to a tail for restoring balance but they are far better protection from falls compared to a chin.

3455434687 11y ago

If the fist evolved to punch: http://www.latimes.com/science/sciencenow/la-sci-sn-human-fist-punching-evolution-males--20151021-story.html http://www.latimes.com/science/sciencenow/la-sci-sn-human-fi... ...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 11y ago
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 11y ago
  "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 11y ago
    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 11y ago
      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_or_Hooks.22_variation https://en.wikipedia.org/wiki/Rear_naked_choke#.22Body_Lock_... . 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 11y ago

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-chins-a-scientist-explains-the-enduring-puzzle http://www.npr.org/2016/01/29/464893281/why-do-humans-have-c... In short. It's unlikely to be for protection, or for sexual selection, or to aid in speech. Go to the interview detailed explanations.

rquantz 11y ago
It doesn't say it's unlikely to aid in speech, just that it's unlikely to be reinforcement for the stresses caused by the tongue while speaking.
bcook 11y ago
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.
deleted 11y ago
[deleted]
vacri 11y ago
"unlikey to be" is not "isn't". The counter to each of those items in the article is one researcher saying "yeah... I don't really think so", not something that's set in stone.
ScottBurson 11y ago
Well, here's what this article says about speech: Others have suggested that the chin is an adaptation for chinwags: It resists the forces we create when speaking. After all, speech is certainly a feature that separates us from other living animals. But there's no good evidence that the tongue exerts substantial enough forces to warrant a thick chunk of reinforcing bone. That's not my first thought at all. I think it has absolutely to do with speech, but not for that reason. I think it's to create more space for the tongue to move around and make different sounds. Just another SWAG, of course, but I'm surprised not to see this idea floated.

colinramsay 11y ago

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.

lawpoop 11y ago

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.

rquantz 11y ago
What an excellent idea. My first thought was that it must have something to do with speech or expression – maybe having a protruding bone bobbing up and down somehow makes speech more comprehensible? The idea of it contributing to facial expressions seem more likely though. Hopefully someone here will take up this line of inquiry.
- dalke 11y ago
  The article mentions that hypothesis: > Others have suggested that the chin is an adaptation for chinwags: It resists the forces we create when speaking. After all, speech is certainly a feature that separates us from other living animals. But there's no good evidence that the tongue exerts substantial enough forces to warrant a thick chunk of reinforcing bone. “And any mammal that also communicates vocally or suckles or engages in complex feeding behaviors that involve the tongue are probably experiencing similar stresses and strains, and they're not getting chins,” says Pampush. Nor should we think that extra structure for complex sounds are needed for a language or comprehensibility. Consider the Silbo Gomero Language, which is "a whistled form of a dialect of Spanish." It "has only 2 vowels and 4 consonants, according to the official nomination document submitted during the UNESCO convention." (Quotes from Wikipedia.) Verbalized Morse code is another example of how simple vocalizations are all that are needed for a comprehensible language.

robotcookies 11y ago

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.

deleted 11y ago
[deleted]
dalke 11y ago
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.

whybroke 11y ago

>We're the Only Animals With Chins... Is the author an Elephant?

nsns 11y ago

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 11y ago
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 .

jondubois 11y ago

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

andrewflnr 11y ago
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?
bitwize 11y ago
That's Zilla, not Godzilla.

c3534l 11y ago

It would appear to me that Tarsiers have a slight chin: http://www.skullsunlimited.com/userfiles/image/variants_large_4225.jpg http://www.skullsunlimited.com/userfiles/image/variants_larg... 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-main-original-1415041962.jpg https://boneclones.com/images/store-product/product-1169-mai... 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%20Skull.png http://www.store.dinosaurgeorge.com/images/Siamang%20Gibbon%...

mmanfrin 11y ago

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 11y ago
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 11y ago
  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).

jondubois 11y ago

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

nonbel 11y ago

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

strait 11y ago

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.

MonadQueen 11y ago

Some of us have more than one chin! http://openborders.info/wp-content/uploads/2099/12/paulgraham2.jpg http://openborders.info/wp-content/uploads/2099/12/paulgraha...

jondubois 11y ago

Actually I found an animal with a chin: Hemiramphus brasiliensis http://www.sosdom.lautre.net/Pages_Glossaire/AGlossImage_Faune/Balaou.jpg http://www.sosdom.lautre.net/Pages_Glossaire/AGlossImage_Fau...