What animals have chins?

Elephants, manatees and we modern humans are the only animals with chins; whether sculpted, cleft, weak or strong ones. No other members of the animals kingdom aside the three animals mentioned above have been observed to have chins. 

What is a chin?

A chin is basically the lump of bone that protrudes forward from the anterior part of lower jaw (underneath the lower lips), and for some mysterious reasons, only elephants, manatees and modern humans (you and me) and known to posses one.

Our closest living relatives, the chimpanzees, gorillas and bonbons don’t actually have this protrusion, despite the strong similarities we share with each ine of them.

Their jaws basically slant backwards from their teeth instead of creating a bone that actually makes a protrusion underneath their lower lip. Even archaic human species like the Neanderthals and homo erectus had no chin, their jaw morphologically terminated in a flat vertical plane.

The chin is actually the main characteristics that set modern humans apart from their archaic ancestors, and indeed, scientists are fond of employing this feature as a way of distinguishing between our skulls and those of these extinct relatives; the Neanderthals, homo erectus, etc.

Our chin is the only trait that uniquely and exclusively belongs to us, not big brains or bipedal as these extinct relatives of ours and other members of the mammalian group also had/have them respectively. So there we go, something to at least stroke on and be highly confident about!

How does the lower jaw area of other animals look like?

Aside from the three animal groups mentioned above, all other skull-possesing members of the animals kingdom have lower jaws that immediately slope inwards from their lower teeth, meaning there’s no bony extension in front of their jaw to act as chins (take a look at the picture below).

In humans, elephants and manatees however, the lower jaw extends beyond the lower teeth, birthing a small bony protrusion which acts as the “chin”.

What animals have chins

Why do humans have chins?

The question why humans have chins is one that has been in existence for more than a century now and has close to a dozen postulated theories seeking to provide an answer. But surprisingly, almost all of these theories have fallen flat against scrutiny, with each having one of them having their own major poke that primarily dilutes the possibility of the theory being an answer.

There are very few theories, often the newer ones however, that have not yet been proven wrong by evolutionary biology, either because they’re still under scrutiny or have indeed undergone one but still managed to stand firmly up against it, but even these theories have not yet provided substantial enough evidence to be able prove clearly the case for their claim. Maybe somewhere in the future they would, who knows?

Anyways, it’ll be unfitting to start a talk on the theories explaining the reason behind the protrusion that made Jay Leno a hollywood hit without actually mentioning one or two of them. So here are some of the postulated theories and the holes poked at them from recent revisions.

Postulated theories

  • Chins are there to help us chew food, they help relive the jaw against mechanical stress encountered when masticating food.

Scrutiny: If the chin was actually meant to buttress the jaw against mechanical stress encountered when chewing, then for a strange reason, its in the wrong position. Stress is more prominently observed in the inner face of the join between the two distinct halves that make up the lower jaw than in the outer face of this join. If at all the jaw needed reinforcement, then the chin should have been positioned inside, relieving stress on the inner face of the join rather than on the outside. And this is exactly what is seen in the case of chimpanzees and macaques, they have a bony addition near the inner face of their lower jaw join called simian shelf, which helps relieve masticating stress.

Scrutiny 2: Humans don’t actually have a tough time masticating food (as many researches have shown), and that is by part even evident in the nature of food that we consume: soft and cooked food.

  • Chins are there to help us speak, they help us resist the force we create when speaking. We are the animals with the most advance collection of speeches by the way.

Scrutiny: There is actually no strong evidence whatsoever that shows that the tongue exerts substantial amount of force that would require some sort of support from a shooting bone placed at the anterior part of the lower jaw. If the tongue did indeed exert such force, then placement of the chin bone is unjustified for because, just as with chewing, the inner face would require the additional reinforcement and not the outer face. Another thing is that, besides we humans that have the most extensive speech repertoire among all primates, there are other animals too that also communicate vocally, work with their jaws in a complex fashion: suckling and even chewing on tougher food than us. Obviously they’d be subjected to similar stress situation, but they are not getting any chins are they? 

  • Sexual selection created the chin in order to help us attract mates. They’re the equivalent of peacock tails, whale songs or the large flanged orangutan faces.

Scrutiny: Throughout the history of evolutionary biology, sexually selected traits have only been found in one biological sex and not on both. Having chins in both human males and females would be the first time evolution has produced the same sexually selected trait in both biological sex. The same? To attract who then?

  • Chins are there to help humans deflect punches to the face. An adaptation of natural selection.

Scrutiny: This would mean that the modern ancestors of humans were clumsy enough to have punched themselves every so often on the face to develop such kind of adaptation. It’s highly unlikely and very unrealistic. In addition to that, the chins are actually very terrible at deflecting blows. They don’t distribute the incoming force very evenly and would most likely leave the recipient with a broken jaw. You can try that and see for yourself, or maybe you shouldn’t.

  • Chins are spandrels, non-adaptive traits that resulted when our faces shrank with time. Our archaic ancestors had bigger faces and we evolved smaller ones, so jaws are perhaps the remanats of this shrinking process

Scrutiny: Possible explanation

  • The chin is the bit of the jaw that remained when the rest shrunk back, similar to the shrinking theory above. As humans began to eat softer and softer food by cooking them, they relieved so much stress on their teeth which caused the teeth to retract back into the mouth overtime. While this retraction happened, part of the lower jaw that held these teeth remained instead of sucking back along with it. This portion of the jaw is what is identified as chin today.

Scrutiny: Possible explanation

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Cite this Article (APA Format)

Bunu. M. (2020, May 19). What animals have chins?. Retrieved from http://emborawild.com/what-animals-have-chins/

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