<link rel="stylesheet" href="//fonts.googleapis.com/css?family=Roboto%3A300%2C400%2C500%2C700%7CRoboto+Slab%3A400%2C700">Chin up: why did humans evolve unique chins? - Filthy Monkey Men

What makes Homo sapiens unique? I could waffle on about art and technology, but other human species made them. In reality, only a handful of anatomical differences separate us from close relatives like Neanderthals. Like the fact that we’re the only human species with a chin 1.

Human and Neanerthal chin
Chin chin, chaps

The chin takes the cake for being the weirdest modern human feature. Sure, there might be more prominent ones; but most of them seem to have a purpose. Our skulls are different shapes, but that gave us differently shaped brains. But what’s the point of a pointy chin?

It turns out this isn’t a new question. Whilst we’ve known it was weird since the time of the Ancient Greeks, but it wasn’t until the Victorians arrived on the scene people started trying to explain the why. And their methods for investigating this were. . . interesting2:

This is brought up way too casually for my liking. Like half person half cows were a dime a dozen in Geneva

Have we got any better explanations (relying on less creepy evidence) since the 1800s? Join me as we explore the top three hypotheses for why we have a weird chin.

1. Chins are sexy

Sexual selection refers to traits that evolve because they appeal to the opposite sex, increasing the chances of reproduction. It’s long been the go-to explanation for any weird trait; particularly in humans. Even Darwin used it, suggesting facial hair was the result of sexual selection.

So obviously, sexual selection has also been invoked to explain to explain our chin.

And the evidence for it does seem rather compelling. If sexual selection is at work, you’d expect the preference for a strong chin to be widespread. Sure enough, research has shown large swathes of the female population liked it3.

However, a common problem with this sort of research on evolutionary psychology is that it never checks to see if these preferences translate into different reproduction rates. Which it would have to for evolution to actually work. In an effort to counteract this failing, some researchers looked at mandibles over time and space. If there really was some evolution at work, they should all be trending towards chin perfection4.

It turns out they weren’t, providing a sound refutation of the sexual selection hypothesis4.

Chin shape around the world
The outlines of chins from around the world, showing variety is the spice of life4.

2. Worlds strongest chin

Sexual selection is a pretty handy way to explain the evolution of features that don’t seem to serve a purpose. However, what if the chin actually does have a function?

Which raises the question: what impact does the chin actually have on us? Well, for decades researchers have been studying the face to find out what impacts our unusual mandible has. Ultimately, they’ve found two key ways it differs from other members of our family.

  1. The bone is a bit thicker
  2. It provides a bit more space in the mouth
Chins of different species
Chins of different species1.

These few changes have enabled endless speculation about the possible function of the chin.

For example, perhaps, the extra thickness in the bone provides support when biting1. Our jaw is unusually strong, after all, thanks to its decrease in size concentrating the force over a smaller area. Thicker bones might be necessary for dealing with these additional forces.

Our shrinking jaw could also mean a chin provides another advantage. Perhaps it provides providing extra space for the soft bits so they don’t get in the way of our breathing5. The extra space the chin provides could also give the tongue more room, helping us talk1.

However, much like sexual selection; there’s little research out there showing that any of these features actually have an impact on reproduction. Additionally, our chin has a fair bit of variety around the world4. If our chin was evolving for an important reason, like stopping us choking on our tongue, this sort of variety could be catastrophic for survival and would be soon purged from the population. Yet it’s still there.

Chin shape around the world
Remember this? It’s not the sort of variety you’d expect to see if the chin was crucial for survival4.

3. An accidental chin

Obviously, evolution includes an element of randomness. As such, not everything necessarily evolved for functional reasons. Sometimes traits become common through chance, or as a side-effect of other changes. Could the chin be an example of such a change?

Well, there certainly are a large number of changes that have happened to our face during the course of human evolution. Many of these seem to have countless knock-on effects across the rest of the skull (and vice versa)6. It’s easy to imagine how the chin might be one such trait.

Facial changes between humans and Neanderthals. Any could have had a knock-on effect on the chin7.

This is particularly likely since our chin isn’t only influenced by facial change. It also seems to be impacted by testosterone during growth. However, during the course of human evolution it’s speculated that there was selection for lower testosterone to stop us being so fighty and help us co-exist. Could our chin be a side-effect of us all getting along7?

Given the lack of evidence for an adaptive origin of the chin and the fact it’s well integrated with these other bits of the body; this explanation does seem the most likely (although given the paucity of evidence for the other ideas, this isn’t saying much).

Ultimately, our unique chin might be an evolutionary accident. Learning our “special” features are random side effects would be good for our species’ ego. We should be taken down a peg.

References

  1. Pampush, J.D. and Daegling, D.J., 2016. The enduring puzzle of the human chin. Evolutionary Anthropology: Issues, News, and Reviews25(1), pp.20-35.
  2. Wallis, W.D., 1917. The development of the human chin. The Anatomical Record12(2), pp.315-328.
  3. Rhodes G, Chan J, Zebrowitz L, Simmons LW (2003) Does sexual dimorphism in human faces signal health? Proceedings: Biological Sciences 270: S93–S95
  4. Thayer ZM, Dobson SD (2013) Geographic Variation in Chin Shape Challenges the Universal Facial Attractiveness Hypothesis. PLoS ONE 8(4): e60681
  5. Coquerelle, M., Prados-Frutos, J.C., Rojo, R., Mitteroecker, P. and Bastir, M., 2013. Short faces, big tongues: developmental origin of the human chin. PloS one8(11), p.e81287.
  6. Mitteroecker, P., Gunz, P., Neubauer, S. and Müller, G., 2012. How to explore morphological integration in human evolution and development?. Evolutionary Biology39(4), pp.536-553.
  7. Cieri, R.L., Churchill, S.E., Franciscus, R.G., Tan, J., Hare, B., Athreya, S., Holliday, T.W., Nowell, A., Steele, T.E., Weaver, T.D. and Wrangham, R., 2014. Craniofacial feminization, social tolerance, and the origins of behavioral modernity. Current Anthropology55(4), pp.000-000.

Related posts




3 Comments

Figure Stones · 8th April 2019 at 12:07 pm

Hi Adam, where did you get the chin comparison picture from? Is it yours? Just in case I use it, I want to give attribution.

    Adam Benton · 8th April 2019 at 12:29 pm

    It’s got a citation dude.

      Figure Stones · 8th April 2019 at 6:28 pm

      Yeah, Thanks, I just didn’t see the tiny 1 figure.

Leave your filthy monkey comments here.

This site uses Akismet to reduce spam. Learn how your comment data is processed.