KnowHOW team explains: As humans evolved, much of the thick hair on the body disappeared ? except those tufts above our eyes. Scientists are not sure what caused this, but they have some pretty good guesses.

Anthropologists say that the brows are meant to keep moisture out of our eyes when we sweat or it rains heavily. This must have been a huge advantage amid the African savanna when our ancestors went out for hunting expeditions. Those wild chases caused profuse perspiration and the arch-shaped brows would conveniently divert sweat to run down the face. And during heavy downpour the brows would help them get a clear vision, draining away irritating rainwater.

Eyebrows are also believed to be an aid to non-verbal communication or facial expressions. Their position emphasises expressions on human face, thus giving others an accurate picture of an individual’s mood. By raising or lowering our eyebrows we can express a variety of emotions. When language hadn’t evolved, the ability to communicate intentions from a safe distance might also have helped early men read others’ minds. Eyebrow-signalling can still be found among several primate species.

Eyebrows are also one of the most distinctive features that make up our faces. Shave them off and you may not be recognised even by your best friend.

The question was sent by Piyali Sengupta, from Salt Lake