Humans may have a surprising evolutionary advantage: Expressive eyebrows

It's one of the first things you notice when you look at archaic human relatives in a natural history textbook or museum. Just above the eyes rests an imposing feature, a prominent brow ridge that juts out above the eye sockets. But why did many of our distant relatives have this distinct facial feature? Why don't we have it anymore? Over the years, scientists have suggested plenty of solutions.