National Geographic : 2005 Sep
THE SCIENCE OF THINGS Who PALEOANTHROPOLOGY Out of Africa Are we lookingfor bones in all the rightplaces? Scientists are good at finding logical patterns and turn ing data into a coherent narrative. But the study of human origins is tricky: The bones tell a complicated story. The cast of characters keeps growing. The plot keeps thickening. It's a heck of a tale, still unfolding. More than half a century ago the great biologist Ernst Mayr surveyed the field of paleoan thropology and saw all sorts of diverse characters: Peking man, Java man, and Homo erectus. He figured out that they were all the same thing and helped bring coherence to a rambling tale. By the 1960s the textbook version of human origins looked pretty tidy: Humans evolved in Africa; Homo habilisbegat Homo erectus, who begat Homo sapiens. (The Neandertals were sort of a fly in the ointment.) Today the field has again become a rather glorious mess. The central fact of human evolution is a given-humans PHOTOILLUSTRATIONBYCARYWOLINSKY descended from a primate that lived in Africa six or seven mil lion years ago-and those who would doubt evolution are argu ing against the entire enterprise of science. But even though the basics are established, some key details are still unknown. "Our family tree is no dif ferent from that of any other animal. There are a lot of dead ends in it. At certain times you had three, perhaps four species of hominins" says Hans Sues, a paleontologist at the National Museum of Natural History in Washington, D.C. The fossil record is hampered by the fact that bones don't fossilize everywhere. We have essentially no fossils, for example, of chimpanzees, because they live in rain forests, where bones decompose rapidly. "We're miss ing a whole swath of habitat," says Dan Lieberman, a Harvard paleoanthropologist. Lieberman says that it's time for a new Mayr to come along and figure out what it all means. Lieberman thinks some of his colleagues have tried too hard to tell the story of human origins from a relatively limited set of fossils, particularly those found in the Rift Valley of East Africa. Knew? "We're not doing a very good job of being honest about what we don't know," says Lieberman. "Sometimes I think we're trying to squeeze too much blood out of these stones." Lieberman's suggestion raises hackles. Tim White, a paleoan thropologist at the University of California at Berkeley who works in East Africa, says: "People who look for fossils focus on the places with the highest potential. If Lie berman or Sues have good ideas for where others should be look ing, why don't they share them?" Earth doesn't yield a perfect database. Still, it's our scientific impulse to impose parsimonious explanations on complex prob lems in the same way that Newton realized that the fall of the apple and the motion of the planets were governed by the same sim ple force called gravity. But the process of evolution can't be observed like the fall of an apple. Life-despite all the efforts of modern science-is messy. -Joel Achenbach WASHINGTON POST STAFF WRITER WEBSITE EXCLUSIVE For more about human origins, and for links to Joel Achenbach's work, go to Departments at ngm.com/africa.