Human faces are relatively flat. Alas, evolution has worn away the jutting jaw and the bulging brow ridge.
Fortunately, we still have one reliable landmark: the eyebrow.
According to a study by MIT behavioral neuroscientist Javid Sadr and his colleagues, eyebrows have remained on our faces because they are crucial to facial identification. Faces without eyebrows are like land without landmarks.
The study: Volunteers were asked to identify fifty famous faces, including that of former U.S. president Richard Nixon and actor Winona Ryder. The photos were digitally altered and displayed either without eyebrows or without eyes. When celebrities lacked eyes, subjects could recognize them nearly 60 percent of the time. However, when celebrities lacked eyebrows, subjects recognized them only 46 percent of time.
The lesson: eyebrows are crucial to facial identity -- they're at least as important as your eyes, if not more so. If you put colored contacts in your eyes, pumped collagen into your lips, or put on a pair of funky sunglasses, people would probably still recognize you easily. But try shaving off your eyebrows. Chances are that everyone will say they didn't recognize you at first glance.
As Sadr points out, eyebrows pop out against the backdrop of your face -- and for that reason not only identify who you are but how you're feeling. Along with the lips, they may in fact be the most expressive part of your body. The single raised eyebrow is a universal sign of skepticism, and the dual raised eyebrow a sign of surprise.
The shape of your eyebrows also reveals, in a glance, a lot about your age and other characteristics. Bushy, gnarly, salt-and-pepper brows: older alpha males. Thin, graceful arcs: young, stylish women. Sparse, light brows: youths. Waxed and tweezed, the brow can advertise good grooming.
Eyebrows sometimes meet each other halfway across the bridge of the nose, especially on men, to form a monobrow, which resembles the vanished browridge of our primate ancestors. Distinctive? Yes, and also brow-raising.