What is the purpose of eyebrows?
Dear Straight Dope:
Please, enlighten me: what is the function of the eyebrows? Why are they on our face? I've spent the last few days staring at eyebrows as a predominant feature on the human head. It's a very strange exercise to do; it makes everyone look pretty unattractive.
This has come up repeatedly elsewhere on the Net over the years. The consensus is that eyebrows keep moisture (sweat, mostly, but also rain) from running down one's forehead and straight into the eyes. This explanation has the advantage of being quite easily demonstrated, fitting the morphology involved (notice the distinct slant of the brow hairs, which conducts water sideways), and having a logical survival advantage. There have been one or two comments from people who were, for one reason or another, temporarily without eyebrows who claimed the difference was noticeable. I've always been content with that explanation. It may not have much impact on a modern human's life, but next time you're hunting (or being hunted) on the African savanna, try shaving off your eyebrows and see if salty sweat running in your eyes makes the task any more difficult. I'll bet it does.
SDSTAFF McCaff adds:
Had it happen (burned off) to one eyebrow. The effect was quite noticeable in rain.