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Why Do Humans Have Chins?

Woman sitting in cafe in thoughtful post with finger on chin

The chin, though it certainly doesn’t get the same amount of attention as the eyes or the mouth, is one of the most defining features on our faces. Whether large or small, cleft or smooth, your chin plays a vital role in lending your face its unique shape—square, oval, round, heart, or something in between.

But what does a chin, well, do? They don’t serve any obvious purpose, like the eyes and mouths. They don’t even help with eating, like the jaws and lips. However, is a chin useless, or does it have some purpose that’s not apparent at first glance?

In short, we don’t know, but we do have some theories. Here are scientists’ best guesses at the purpose of the chin.

Alone with Our Chins

When it comes to the chin, we’re all alone in the natural world. No other animals, not even our closest relatives, primates, have chins.

Although our habit of anthropomorphizing can make chimpanzees and gorillas look like they have chins, when you examine their bone structure, you’ll see that the lower jaw simply slopes away from the teeth, with no extra protrusion to form a chin. Even Neanderthals didn’t have chins.

Of course, there are lots of other things that humans have, but that other animals lack. Speech, technology, writing, and civilization all come to mind. Does the chin somehow have something to do with these other differences? Let’s take a look at the prevailing theories.

Chins Might Help Us Speak

One proposed theory is that the chin is the result of the small strain on the jaw that happens each time we speak. The movement of the tongue muscles during speech creates stress in the jawbone, which can cause tiny cracks. The chin’s extra bone might be an adaptation to help keep that strain from causing a bigger problem. Basically, the chin functions as a sort of speech shock absorber, according to this theory.

However, scientists don’t really think that this theory holds water. After all, other animals also do things that put a strain on the jaw, such as make vocalizations, and they don’t need chins.

Chins Could Help Us Eat

If speech isn’t the reason, maybe eating has something to do with it. The same theory applies here—the extra bone of our chins might absorb the shock created when we chew.

But this theory also doesn’t hold up, for the same reason as the last one. Our primate relatives with jaws like ours don’t need chins to help them eat, so why should we? Plus, chins are actually placed in the wrong location to strengthen our jaws during chewing. We’d need extra bone on the jaw’s inner wall if it were to serve that purpose.

Maybe Chins Attract Mates

Chins play a significant role in our overall appearance, so maybe they have something to do with how we find romantic partners.

However, traits involved in sexual attraction usually only appear in one sex or the other. For example, a fish might choose a mate based on how colorful a fish of the opposite sex is. Male and female fish usually have different colors and sizes, which makes it easier for them to choose mates of the opposite sex. But when a trait is present in both genders, it’s typically not a factor in sexual selection.

Men and women both have chins, so it doesn’t seem likely that this is a trait we evolved to help us choose mates. On to the next theory!

Perhaps Chins Protect from Punches

One of the funnier theories of chin evolution is that these features protect us from damage to the face and neck.

While this seems plausible at face value (pun totally intended), just imagine the number of punches early humans would have had to throw to make this a feature of natural selection. Blows to the face would have had to be a daily norm, which just doesn’t make sense. After all, humans adapted to live communally. Sure, we’ll have the occasional battle, but constant fighting just doesn’t fit with our history.

Chins also don’t hold up that well in a fight. The jaw can break with a single well-placed blow to the chin, making it a poor defense mechanism.

Chins Might Have Once Held Bigger Teeth

Here’s a more realistic theory: chins first existed to support the bigger teeth early humans needed. Our ancestors had much larger teeth, which they used to tear through raw meat. But when our diets changed as we started to cook our food, our teeth gradually got smaller, along with other facial features.  But there was no reason for the chin to shrink along with the teeth, so it stayed in place.

Chins Could Be an Evolutionary Byproduct

The previous theory demonstrates a type of evolutionary spandrel or a trait that developed as a byproduct of evolution, not as an evolutionary advantage in itself.

The chin could easily be another sort of spandrel, a byproduct of a change that we haven’t thought of yet. Maybe as we developed other modern characteristics, the chin happened as a sort of random result. Many “chin experts” believe this is the most realistic explanation at all, although it doesn’t give us much in the way of hard answers.

Who would have thought that the humble chin could hold so much mystery? The secret to why we became modern humans, while our relatives like the Neanderthals died out, might lie in figuring out what caused the chin. While it’s not the most pressing scientific question, it’s interesting enough to keep a small group of researchers committed to finding the answer. Whether a useful development or an evolutionary accident, that answer is sure to be enlightening—whenever we finally find it.

Elyse Hauser Elyse Hauser
Elyse Hauser is a Seattle-based writer and editor with a Master's in Writing Studies from Saint Joseph's University. Her work has appeared in publications like Racked, Vine Leaves Literary Journal, and Rum Punch Press. She was awarded a 2017 Writing Between the Vines residency.  Read Full Bio »