Why do we have eyebrows and other types of facial hair?

We humans seem to have an affinity for facial hair.

Prehistoric cave paintings reveals the myriad tools used by our ancient ancestors for shaving: shark teeth, sharpened flints, and even clam shells. Nowadays, beards are back in fashion and people are they touch their eyebrows with a razorinstead.

But is there a reason we evolved to have these furry trinkets? And if so, for what evolutionary advantage can we give it up staying on trend?

It turns out that researchers have something to say on the matter. Learn their answers to why we have eyebrows, what eyelashes are for, and why we grow beards.

Why do we have eyebrows?

Let’s start with those fuzzy caterpillars on the top of the face.

Eyebrows do a great job of preventing moisture like rain and sweat from getting into our eyes. Everything from the angle at which these hairs grow to the shape of the brow arch is designed to direct moisture away from the face.

Of course, while protecting our peepers may have been their original purpose, eyebrows ended up playing a secondary role somewhere along the line: conveying emotion.

What are eyebrows for?

A 2018 survey published in Natural ecology and evolution analyzes why the eyebrows of early hominins were much larger and stiffer than the edges of modern humans. They found that—contrary to some prevailing theories that ridges structurally reinforce the skull or aid in biting mechanics—having more mobile eyebrows likely helped our ancestors form relationships and ensure survival in groups.

Read more: What did ancient people look like?

Eyebrow hairs, the researchers say, simply increase the visibility of this form of communication.

Oddly enough, evolutionary psychologists say that canine eyebrows have undergone a similar journey; centuries of domestication “transformed the anatomy of the facial muscles of dogs specifically for face-to-face communication with humans,” write the authors of 2019 survey published in PNAS.

As if we needed another reason to love our canine companions.

What are eyelashes for?

The same goes for eyelashes, which have the additional task of blocking solid particles like dust. And according to a 2019 survey who look at eyelashes from a chemical engineering perspective, they may even help prevent dry eyes by limiting unwanted evaporation.

For those who are curious, the research team determined the “optimal lash length” to be about 15 to 30 percent of the width of the eye—resulting in up to a 30 percent reduction in evaporation. Maybe it’s time to ditch those eye drops and get out the tape measure?

As for the lower half of the face, theories abound.

Why do we grow beards?

In his The origin of man, Charles Darwin proposed a reason why we grow beards. He said beards are an example of sexual selection and may have evolved “to charm or excite the opposite sex” — while intimidating the competition. Researchers tend to think the same way, for example, about lion manes, which can signal to other lions that the wearer of the mane is in good health and a formidable opponent.

Read more: It’s rare, but a lioness can grow a mane

But does this theory hold up in the modern age?

A 2019 survey published in Psychological science suggests that it is possible; the researchers found that “the presence of a beard increased the speed and accuracy with which participants recognized expressions of anger.” The same cannot be said for expressions of happiness or sadness, emotions that definitely do not serve to intimidate.

Are beards protection?

But don’t take that to mean beardies are all barkers and no bites. A study recently published in Integrative biology of the organism suggests that the fuzzy face protects vulnerable areas of the jaw from damaging blows during combat.

By making a fibrous epoxy composite to serve as an artificial bone and covering it with thick, woolly skin cut from sheep, the researchers found that this model absorbed 37 percent more energy from a blunt impact than samples without hair. In addition, the models with hair “failed” — in other words, broke bone — only about half of the time, compared to nearly 100 percent of the composites without hair.

(They note that results may vary, however, depending on how thick the beard can get.)

Now that you know why we have eyebrows, what eyelashes are for, and why we grow beards, you might be wondering if we are losing the hair on our heads.

Read more: Why do people go bald?

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