January 4, 2012
Why Do Humans Have Chins?
Humans are the only hominids with true chins. Image courtesy of Wikicommons
When you think about what makes modern humans unique, the chin is probably not the first, second or even third thing that comes to mind. Yet this bony protrusion at the end of the lower jaw is not seen in any other hominid species. So what’s a chin good for? Over the years, researchers have thought up a variety of explanations for why we have chins.
Perhaps the most common explanation is that our chin helps buttress the jaw against certain mechanical stresses. Ionut Ichim, a Ph.D. student at the University of Otago in New Zealand, and colleagues suggested in the journal Medical Hypotheses in 2007 that the chin evolved in response to our unique form of speech, perhaps protecting the jaw against stresses produced by the contraction of certain tongue muscles. Others think the chin evolved to safeguard the jaw against forces generated by chewing food. Last year, Flora Gröning, a biological anthropologist at the University of York in England, and colleagues tested the idea by modeling how modern human and Neanderthal jaws withstand structural loads. Their results, which they reported in the American Journal of Physical Anthropology, indicated the chin does help support the jaw during chewing . They suggested the chin may have evolved to maintain the jaw’s resistance to loads as our ancestors’ teeth, jaws and chewing muscles got smaller early on in our species’ history.
A completely different line of reasoning points to sexual selection as the driver of the evolution of the chin. Under sexual selection, certain traits evolve because they are attractive to the opposite sex. Psychological research suggests chin shape may be a physical signal of the quality of a mate. For example, women may prefer men with broad chins because it’s sign that a man has good genes; likewise, a woman’s narrow chin may correlate with high levels of estrogen. Zaneta Thayer, a graduate student at Northwestern University, and Seth Dobson, a biological anthropologist at Dartmouth, examined the sexual selection hypothesis by measuring the chin shape of nearly 200 skulls in a museum collection, representing people from all over the world. The pair discovered that there is a small but distinct difference in chin shape between the sexes, with men having a taller, more pronounced chin. They argued in the American Journal of Physical Anthropology in 2010 that this difference is evidence against explanations that the chin evolved to resist mechanical stress. If chins evolved in response to eating or talking, then there should be no difference in chin shape between the sexes because, presumably, men and women eat and talk the same way.
Maybe the evolution of the chin is more complicated than any one scenario. For example, is it possible the chin initially evolved to handle particular mechanical stresses and was later shaped further by sexual selection? I’d like to see someone test that idea.
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The simple answer is to help protect the front teeth during a fall. Next question?
In other words, no one really knows.
To complete you face!
We have chins so that we may fold towels.
Don’t know if anyone has considered this yet…
As hominds developed the power of speech we also increased the likelihood of being struck by other hominids. The chin developed as a defense against being punched in the mouth.
Men and women developed different chins because men are more likely to say things that result in a punch to the face. So, males developed a stronger chin.
This is all said tounge in cheek, or chin, of course.
God gave us chins to provide a drip edge so the gravy will hit our ties smack dab in the middle. Also, as a good target for the wife’s left hook when we get gravy on the tie she gave us for Christmas.
The sexual selection idea has some merit if one considers the number of cosmetic chin implants per year. A receding (or “weak”)chin is not deemed very attractive to either men or women. However, the receding chin trait still shows up modern people around the world,and I wonder why this is so.
Why do we have chins? That’s easy — so we can think!
See: artcyclopedia.com/feature-2001-08.html
Sexual selection. A raised chin communicates high status, which is to women what fertility proxies are to men.
Maybe it is protection in falling. I have scuffed up my chin a lot more times that I have my teeth, nose, and forehead when falling. Not to many other animals stand with there head as high with only two legs.
Spandrels…
Adaptation is not the only answer.
A combination is likely the most sensible answer – the chin came into its primary existance to buttress the jaw, which is of vital importance, and then having a good chin became a sign of having good genes, and thus sexually attractive.
There is a well known phrase amongst not only the English speaking world and that is “chin up”
. This not only shows that we can be defiant by this posturing but that it can also bring us ’round’ so to speak – as in “get yourself together, my friend, as there is little time for indecision. More, so it is generally used as a term for- “get with it, switch on and let’s go again”. No time for rumination, (you ruminant?). It is a distinctly human idea that could only arise due to the fact that we have ‘a chin’. There are many other and varied uses for this term and not only in the biological sense. If anyone should suggest that I speak crap then I will “take it on the chin!”.
I am pretty sure that the answer is simple interaction of two variables:
a) As man increasingly became upright, the jawline remained constant and the face and cranium moved forward, and the teeth moved inward. This would have the consequence of giving us a pointier chin. (It’s impolitic to note, but people prefer less apelike features in selection so that’s built into us somehow as well as a desire for symmetry, height, and long legs.)
b) As the author notes, testosterone is mostly visible as cheekbones and jaw lines. So women selected males for testosterone. They still do. The younger the more so. (ALthough it is pretty interesting that the waist area is the first thing that people look at in selecting mates of either gender. Men then spend more time on the face to see if there is a chance at acceptance – mating. Women on the details, like hands, feet, and legs.)
There were some side effects to the development of our skull position. For example, the reason we snore is that a) we are fatter than we were in the past and b) when not running every day, there is less exercise of the muscles used to hold the throat open to increase airflow. c) there is less room for our very active tongues with the spine rotated further toward the base of the skill to assist in vertical posture. (We think of ourselves as chimps or gorillas, but we’re really wolves. We chased down prey until it was exhausted, then killed it when it could no longer muster the strength to fight back. No wonder the wolfman is so intuitive. It’s us.)
To fix the snoring problem one needs only move the jaw forward to where our ancestors would have had it, in order to increase the available air space. And of course, lose forty pounds. :)
The suggestion that the chin is merely a byproduct of the reduction in the size of the dental arcade was not included in the article. I think the chin, however, evolved in concert with the evolution of kissing. The chin functions like a “stop”, helping to align the partners jaws and faces in the correct positions for kissing.
Maybe instead of working from the past forward we should try working from the present backwards. In daily speech chins are called ‘weak’ or ‘strong,’ ‘receding,’ ‘cleft’ or ‘pointed,’ and I remember reading a description of someone as having “a chin like an Italian prince” i.e. like the tip of a pointed boot.
All these descriptions are associated with (a) character traits and (b) physical attractiveness; ‘weak’ and ‘receding’ with physical/psychological weakness and ‘strong,’ ‘cleft’ and ‘pointed’ with the opposite, especially in males.
Maybe by using today’s cultural preferences across the globe it would be possible to backtrack through art, history and archaeology to set up a trend or probability? There should be enough raw data laying round to try it.
Thank you Wilson, Neil, TallDave, Austin and especially maureen.
Chin hairs were also found to aid in the protection of habitation structures in the event of predator attack. (in about one out of every three cases, that is)
If the increasing size of the chin is an evolutionary trait, then I assume that Jay Leno is a highly advanced form of human life.
Men and women eat the same way?
Erin there is of course the tuning fork effect used once upon a time by Native Americans and for example the Ancient Greeks which involves positioning the chin in a variety of ways in relation to some sort of resonating cavity such as a dead hollowed out tree still in the ground, drum or in the case of the Australian Aborigines a didjeridoo located somewhere with compatible resonating properties such as the floor or wall of a cave which a skilled operator can use to tune into the location, distance, number and type of activity of animals or enemy warbands coming and going in the distance.
A similar effect can be achieved by carefully biting down on a suitably resonating tool placed on a patch of ground with the right properties and relaxing the jaw so the whole skull becomes a kind of sonar monitoring device.
This may be precisely why the chin evolved in the form it did creating a kind of leading edge for vector detection.
Its so we can stuff pillow cases.
Is it possible that the presence of a prominent chin has to do with creating a visually larger face? A prominent chin and a high forehead produce together a much bigger face, possibly giving the impression of a bigger (and thus more dominant) individual. This is part of the reason people standing upright can dominate much larger animals — we are perceived as the upright, front end of an animal much larger than we actually are.
Another possibility is that the high brow and pointy chin dramatically distinguish our faces from those of other mammals. This seems to be an important distinction in humans, considering how often we insult others by labeling them as some sort of animal.
If neither of those, then I concur with the towel-folding theory.
What exactly might the “good genes” be that are supposedly associated with a broad chin? Have their been any studies showing that people with small, receding chins are on the whole less healthy and vigorous than their big-chinned counterparts?
The chin evolved as humans started thinking more and more and needed something to rest on their thumbs whilst thinking.
Chins evolve, therefore we are more attractive, speak better or something else occurs. We don’t evolve to produce a result, we get a trait because of a gene change which might be selected by nature.
lol Whit, hilarious……no.
I believe the chin evolved as a scoop for digging, sadly humans have yet to realise its use hence why more and more people are loosing a prominent chin…..ofcourse I don’t really believe that, my names not chin, its aaron and I’m from london ooosh…however I personally think as we began the transition from ape to human ish, we began to loose the tooth size of the apes causing the part of the jaw supporting the teeth to in turn get smaller to which left a bony protrusions at the bass we call a chin and I guess this accidental chin creation stayed because it turned out 2 have some kind of benefit, be it sexual attraction, jaw support, shock absorber or as a shovel, it stayed lol interesting subject though
cheekbones are to help eating hard things like nuts and things. i don’t know, watch yourself eating, what’s the chin doing? maybe chins are to help make more facial expressions to communicate with other hominids. like, boo hoo i’m sad. or look at me, i’m heroic.
Expressed chins exist only in species which have vocalization and
have lips participating in sound differentiation. Hominids, some primates, …
Perhaps, flexible lip support, plays a critical role in devdlopment of a chin. BTW this doesnt exclude some of the other reasonings as well.
The chin is there to protect against falls or blows.
Only humans have chins and surely the reason why animals do not have a chin is because they walk on all fours and the likelihood of a severe fall or blow is minimal.
As humans walk on two legs it is inevitable that you will fall over and bang your head at some point or receive a blow. If you receive enough force to your chin as a result of a fall or blow then you can break your neck. Humans would not be here today if you broke your neck every time you fell over and banged your chin or got punched.
However, I believe it is not as simple as to say that there is only one reason why humans have chins.