ZMT: Daily Fact: What's the only animal with a true chin?

Daily Fact: What's the only animal with a true chin?

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Original photo by Thorsten Schmitt/ Shutterstock

Humans are the only animals with true chins.

Humans have a few biological advantages compared to other species. The most obvious is our big brains, which have empowered us to become the dominant species on Earth. But another feature that is often overlooked is our chins — yes, we're the only animals on Earth with true chins. You might be thinking, "Wait a minute, I give my cat chin scratches all the time," or "Surely chimpanzees, our closest animal cousin, sport some kind of chimp chin," and the answer is nope and nope (respectively). When you're scratching the "chin" of your feline companion, what you're really doing is scratching the mandible, i.e., the lower part of the jaw — not the chin, which is the bony part that juts out at the bottom of your face. Elephants and manatees also have chin-like protrusions in their lower jaws, but they don't quite qualify as true chins.

The mystery of why no other animal has a real chin gets even more interesting because past human species, such as Homo erectus and Homo neanderthalensis, didn't have chins either — instead, their faces simply ended in a flat plane. So why did evolution find the need for human chins? Scientists aren't exactly sure. The most prominent theory is that chins help humans chew, but scientists from Duke University and the University of Florida found that chins aren't actually much help there; they technically make chewing more difficult, as they reinforce the wrong part of the face for aiding mastication. Chins also don't help much with human speech, which is another theory that's been suggested, and researchers say it's unlikely they're a mere product of sexual selection or a protection against violence, such as punching. Some scientists think the chin might be a spandrel, a byproduct of other evolutionary changes that on its own serves no real purpose — basically, a happy accident. We may never truly know exactly why humans have these extra bony bits on the ends of our faces, but keep your chin up. After all, you're the only species that can.

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Numbers Don't Lie

Average strength (in pounds per square inch) of the human bite

162

Duration (in seconds) of the world's longest chin stand (1:44:25)

6,265

Years ago the human chin began to form in our ancestors

80,000

Chromosome number containing genetic marker rs11684042, which may indicate the presence of a cleft chin

Scientists aren't exactly sure about the biological reason for beards.

If you're a practicing pogonophile (aka a lover of beards), you may not be too concerned about the reasons behind the time-honored art of beard-growing. However, scientists like to get at the why of things. While hair on our head protects us from the sun, body hair aids in thermoregulation, and hair below the belt protects against bacteria, beards have no known specific biological function. Some scientists have argued that facial hair could aid in protecting the body against ingesting harmful bacteria, but then it'd be likely that women would have evolved to have beards as well. Instead, some evolutionary biologists theorize that beards act as a tool for intersexual attraction regarding women and intrasexual competition with men. In other words, beards subconsciously message virility to women and formidability to men. But as fashion goes, beard popularity trends come and go, and studies show that attraction is often influenced by "negative frequency dependence," meaning if everyone has a beard, preference for clean-shaven faces increases (the opposite is also true). So, just as the beautiful plumage of a male bird is merely a color display to impress a feathered female while intimidating the competition, beards (or a lack thereof) may be a man's own form of peacock posturing.

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Daily Fact: What's the only animal with a true chin?