why do we have eyebrows?



Why do we have eyebrows? I understand most other hairs have the use of blocking something, like dust in our nose(i may be wrong on that as well) but what is the use of eyebrows?

In: Biology

They can help us see in the rain or when we’re super-sweaty, by diverting the flow of water running down our heads and keeping it out of our eyes. Think of them as storm gutters for your forehead.

They’re also a pretty important part of the expressive gestures we make with our faces, so there might be some selection pressures which made them more prominent too.

They keep sweat out of our eyes, and they also emphasise and clarify facial expressions, which assists communication.

Sweat burns in the eyes and humans sweat whereas other mammals don’t—it’s what allows us to have unmatched physical endurance in the animal kingdom. I suspect this is a only one reason why we have eyebrows.

Another reason could be that we’re socially unparalleled in the animal kingdom. I imagine eyebrows allow better communication. To support this hypothesis, we’re the only species with a sclera (white of the eye) which also probably exists to facilitate communication.

There’s no way to know with absolute certainty. That is the nature of evolution: one can make educated guesses and build a hierarchy of hypotheses of varying degrees of certainty, but there’s always uncertainty such as with many of the queerer questions like this one.

To put this into better perspective, look up sexual dimorphism and sexually dimorphic birds; they’re *ridiculous*. We know sexual selection is a real mechanism. Bright blue color signals a chemical composition and abundance of y which implies good health, but *why*, for example, does this particular patch of feathers have this shape? The question of why eyebrows exist is easier to answer, but it’s far less clear in comparison to more fundamental features.