The eyebrows do serve a  function.  Eyebrows function to keep sweat and rainwater out of your eyes.  While this is not important anymore, in primitive times they were very important, for  the human was escaping a predator perhaps they start sweating, that salty water in the eyes would blind them and make them food  for whatever was chasing them. Eyebrows still plays an important role in our culture because they’re useful for communicating nonverbal expression and women seem to enjoy plucking and pruning them to convey themselves to be more beautiful.  Younger people tend to pierce eyebrows, but even with all these things, they still function to wick water from  the eyes  to the sides of the face.  You might consider them the eyes’ is umbrellas.