ANTHROPOLOGIST Robert Franciscus of Stanford University has been studying the Neandertal face for more than a decade, trying to understand its unusual architecture. He specializes on the nasal and facial anatomy of Neandertals, and on what we can learn about human evolution from them. (To his embarassment, a colleague approached him at his first scientific conference and said, "Hey, you're the nose guy!") To fathom why Neanderthals had this combination of features, Franciscus says you need to look at what Neandertals did with their mouth--besides eat.
     Although Neandertals manufactured a wide variety of stone tools, from heavy hand axes to delicate blades, the mouth was a key supplement to their tool kit. From microscopic grooves and wear patterns on Neandertal teeth, scientists conclude that the mouth doubled as a vise for gripping the end of a stick while the hands shaped the other end, and as a tanner's mallet for softening and working animal skins. Straight scratches on the front teeth suggest that Neandertals held food in the mouth while cutting it with stone tools. Continual heavy use gradually eroded the teeth, so that "by the time Neandertals reached their late 30s and early 40s, their teeth were worn down to essentially nothing," Franciscus says. Only smooth nubs projected beyond the gumline.
     Hard, frequent biting may have created another, more serious problem: strain on the facial bones. According to anthropologist Yoel Rak of Tel Aviv University, the Neandertal face represents an evolved solution for dissipating this stress. Over many generations, he says, the bones of the face and jaw became thicker and larger in response to the strain from biting. This shoved the face forward. Rak likens the Neandertal face to a pair of swinging doors that had been pushed partway open. His hypothesis, which he set forth in a 1986 paper, also explains the large Neandertal nose: as the face got bigger, the nose enlarged along with it, just as a nose painted on a balloon would grow as the balloon filled with air.
     One skull feature to which Rak called attention is the canine fossa, the hollow just below the human cheekbone. It's absent in Neandertals. (No Neandertal could ever achieve the sunken-cheeked, fashionably starved look coveted by today's models.) Instead, a wall of bone continues straight down to the teeth--an arrangement Rak claimed strengthened the upper jaw.
     However, Franciscus points out one implausibility in this adaptive story. For natural selection to favor a stronger face, weaker-faced Neandertals must have paid some penalty in survival or reproduction--say, they often fatally shattered their skull while working a stick or gnawing a skin. If Neandertals--or their ancestors--did regularly suffer this kind of injury, the fossil record shows no trace of it.