Humans lost most of their visible body hair a long time ago. That’s the baseline condition of our species. Against that background, a thick patch of hair that appears on the face, in one sex, only after puberty, is an exception that needs accounting for.

The obvious explanations don’t hold up well. It isn’t insulation, since beards grow readily on men whose ancestors lived near the equator. Sun protection is a more interesting near-miss, because facial hair does block a real share of ultraviolet light. But sunlight falls on men and women equally, and on children too, so UV can’t explain a trait that shows up in one sex and only after adolescence.

What biologists can say confidently is what category it belongs to. A beard is a secondary sexual characteristic , meaning a trait that shows up at sexual maturity and differs sharply between the sexes without playing any direct role in reproduction. It’s switched on by androgens, the hormone family that includes testosterone, which is why it arrives on schedule in adolescence rather than being present from birth.

What The Beard Is Probably For

Traits like this are usually explained through sexual selection, the process Charles Darwin proposed for features that survival alone can’t justify. Sexual selection works in two ways. A trait can spread because the other sex prefers it , or it can spread because it helps its owner deal with rivals of the same sex. Those are different explanations with different predictions, and beards give surprisingly different answers depending on which one you test.

The mate-choice explanation is the one most people assume, and it’s the weaker of the two. Preferences for facial hair vary a great deal between cultures, and they shift within a single culture over the span of a decade or two. A 2014 study published in Biology Letters found that each of the four grooming styles it tested, clean-shaven included, looked more appealing to people when it was rare among the faces around it. That reads less like a preference for beards than a preference for novelty.

The rival-competition explanation holds up more consistently. A 2012 study published in Behavioral Ecology showed the same men bearded and clean-shaven to viewers in New Zealand and Samoa, two culturally distant groups, and found that the bearded versions were judged older and higher in social status by both, with no gain in attractiveness at all.

A beard also enlarges the apparent size of the face and squares off the jawline, which is the visual signature people associate with physical formidability. The weight of recent evidence points toward other men being the primary audience for a beard.

Anecdotally, this lines up with what men say about their own choices. Ask someone why he grew a beard and you’ll often hear that he wanted to look older, or to be taken more seriously at work. You rarely hear that he wanted to be found more desirable.

The useful comparison here is a lion’s mane rather than a peacock’s tail. It functions less as an advertisement to potential mates and more as a badge that rivals read, one that can settle a confrontation before it becomes physical. Looking formidable is considerably cheaper than proving you are.

Where The Science On Beards Remains Unsettled

One hypothesis holds that beards also serve a physical purpose by cushioning the jaw against blows. A 2020 study published in Integrative Organismal Biology tested this by dropping weights onto a bone substitute covered in sheep skin, and found the furred samples absorbed noticeably more energy than the sheared ones. It’s a suggestive result rather than a settled one, and it sits awkwardly next to separate research finding no relationship between how bearded a man is and how well he actually fights.

There’s a related argument about whether a beard qualifies as an honest signal, meaning one too costly to fake. Growing a full beard does require years of androgen exposure that a teenager can’t counterfeit. But maintaining one costs nothing, and removing one takes a couple of minutes, which makes it a strange sort of handicap.

It’s also worth saying that beard growth varies more than the general framing suggests. Density is strongly heritable and differs across populations, with many East Asian and Indigenous American men growing sparser facial hair on average. Some of that traces to a common variant in a gene called EDAR.

A 2016 study published in Nature Communications scanned the genomes of more than 6,000 people and found it to be the strongest genetic signal for beard thickness yet identified, the same gene that also shapes scalp hair, sweat glands and tooth form. Facial hair is partly riding on developmental machinery that evolved for other purposes.

One last thing, since it comes up constantly. Shaving does not make a beard grow back thicker. A razor cuts the shaft at its widest point and leaves a blunt tip that feels coarser than a tapered one, but it has no effect on the follicle underneath.

The part that stays interesting is the gap between the trait and its meaning. The hair itself has barely changed across human history, while the message it sends has changed repeatedly, from Roman legions who shaved to Victorian gentlemen who competed over whiskers to 20th-century offices that treated a bare jaw as a condition of employment. Biology supplied a signal. What it says has always been up to us.

Wondering what else about your body other than beards is a leftover signal rather than a useful tool? Find out how well you really understand where we came from with this science-backed test: Evolution IQ Test