Two eyes positioned above a pair of nostrils that are themselves perched above a mouth—such is the layout of the face for vertebrate creatures ranging from sharks to humans. However well that arrangement may be optimized for finding and eating food, among mammals the face has taken on another critical role: communication. Nowhere is this function more apparent than in the human visage.
Primates in general have complex social lives, and they commonly use facial expressions in their interactions with one another. We humans have particularly expressive faces with which we convey such emotions as fear, happiness, sadness and anger. Researchers once chalked up the rich repertoire of human expressions to our having uniquely specialized facial muscles. But physical anthropologist Anne Burrows of Duquesne University has found that, in fact, the chimpanzee—the next most dramatic primate—differs little from humans in the musculature of its mug.
Two features, though, do separate human facial expressions from those of the rest of the primate pack. First, we have distinctive sclerae, or whites, around our irises. Second, our lips protrude from our faces and are darker than the surrounding skin. These traits provide our countenances with strong visual contrasts that may well better telegraph our feelings.
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Exactly when and how humans evolved such animated faces is unknown, but clues might be found in the fossilized skulls of our ancestors. Endocasts—casts of the impression the brain leaves on the interior of the skull—offer insights into the changing capabilities of brain regions over time. In 2000 paleoneurologist Dean Falk, now at Florida State University, led an analysis of endocasts from the ancient hominid Australopithecus africanus, which lived between three million and two million years ago. The results showed that parts of that creature’s anterior temporal region were larger than those of apes. That enhancement might have made this human predecessor better at processing information about visages. If so, our propensity for making and reading faces may have very deep roots indeed.
