The eyebrow is hair above the eyes. Its function is to prevent sweat from dripping into the eyes, blinding vision.
Another possible function of the eyebrow is to enhance the prominence of the brow ridge. The eyebrow contours the brow ridge very closely, in effect making the brow ridge appear more prominent. Having a large appearing brow ridge makes the face appear more masculine, which could be beneficial in intimidating intrasexual rivalries. This function is similar to the effect of the beard of making the jawline more prominent (Puts 2010). Thus, eyebrows could be thought of as a type facial hair because it has an overlapping function to beards and moustaches.
The eyebrow flash is used in many cultures as a greeting. The effect of the eyebrow flash is that it makes the brow ridge less prominent. This therefore has a appeasing effect. Many people unconsciously raise their eyebrows higher as a signal of submission when they nervous around other people (especially strangers or authority figures).
Some women raise their eyebrows to appear more feminine in pictures, as it makes the brow ridge appear less prominent.
Some men do the reverse and squint, lowering their eyebrows.
- Puts, D. A. (2010). Beauty and the beast: Mechanisms of sexual selection in humans. Evolution and Human Behavior, 31(3), 157-175.