ANTHROPOLOGISTS like to imagine a Pygmalion-like experiment that involves releasing a Neandertal in the New York subway. Groomed, slipped into a specially tailored Armani suit, and grasping a cell phone instead of a flint, could he pass as a modern human? TRUE, the average New Yorker might not look closely enough to discern the distinctive Neandertal body hidden beneath the suit--barrel-chested, short-legged, and strong as an Olympic powerlifter. But even the most indifferent subway rider couldn't look a Neandertal in the face without a small shock. Eyes set deep beneath an overhanging brow ridge. A short, receding forehead. A face that juts forward from the rest of the skull, almost forming a snout. An enormous nose--wide, long, and protruding, a combination found in no modern humans. Massive jaws and teeth, particularly those at the front of the jaw--but no chin.      Since Neandertals were discovered about 150 years ago, their reputation has undergone more revisions than Richard Nixon's. Scientists have battled over what Neandertals looked like, how they lived, and where they belong in our family tree. Today, some of these once-hot controversies have cooled into agreement. Most anthropologists concur that if we could look a Neandertal in the eye, we would not be looking into the face of an ancestor. Reflecting this view, modern humans (Homo sapiens), who first appeared in Africa about 140,000 years ago, are now classifed in a different species from the Neandertals (Homo neanderthalensis), who inhabited Europe, western Asia, and the Middle East from about 300,000 years ago to 30,000 years ago.      But the field hasn't gone cold. Just as many questions remain unanswered about the Neandertals and continue to provoke research and passionate debate. For example, Neandertals loom in our imagination partly because of their exaggerated facial features. But why did Neandertals evolve this ugly mug? What function did the bulbous nose, protruding face, and enormous jaws serve? next >>