National Geographic : 1998 Aug
on a large, green-felt-covered table and mea sured each one. Henry had run the numbers, but he wouldn't believe the data until he stud ied the actual bones. After three exhausting days I felt relieved when Henry finally said, "OK." I knew if I could convince him, I could convince anyone. Our analysis yielded some startling results. As might be expected, the africanusspecimens, Lucy's supposed descendants, had heads that that the ability to walk on two legs like a human evolved only once. That bipedalism happened once means it might have happened many times. It may have arisen as a means of traveling between feeding patches. I think bipedalism arose at least twice. Afarensis emerged in East Africa as a human like biped but eventually died out. A second species-africanus-emerged at almost the same time in southern Africa, which may have I FELT RELIEVED.... I KNEW IF I COULD CONVINCE HIM, I COULD CONVINCE ANYONE. looked even more human, but their long arms and short legs were more primitive. They were top-heavy, as if the upper limbs belonged to a male and the lower to a female. For Lucy to evolve into these forms, evolution would have to go backward-which rarely happens. DES THE REALIZATION that africanus had an apelike body mean we're kicking it out of the family tree? Quite the contrary. Discoveries of Homo habilis skeletons in Kenya by Richard Leakey's team and in Tanzania by Tim White and Donald Johanson indicate that the first members of our genus also had long arms and short legs. Perhaps they inherited their odd bodies from africanus. So rather than being the legendary mother of us all, Lucy may be just another branch on our family tree. And that branch might be a dead end: Lucy may have given rise to Australopithecus boisei, a robust australopithecine with big teeth and strong jaws that died out about a million years ago. In fact, africanus shares more features with Homo habilis-alarger brain, shorter face, and smaller canine teeth, for example-than afarensis does. "I think africanus is close to the ancestor of Homo," says Henry McHenry. That reinforces my own conviction that Homo emerged from africanusin southern Africa and migrated north. Our data also challenge the idea stayed forested longer, requiring it to retain the ability to climb trees well. A complex mix of habitats with diverse predators and food sources may have stimulated africanus to become smarter-and its brain gradually to grow nearly as large as that of Homo habilis. As more fossils turn up and scientific meth ods improve, new information will shed light on these questions. Did africanus evolve from afarensis and revert to a primitive apelike body? Or were afarensis and africanus sister species? If there was a common ancestor, what did it look like? Did it have an africanus body and an afarensis head? Whatever the results, one fact is clear: The paths of human evolution are far more complex than ever imagined.  Lee Berger has published his findings in the Journal of Human Evolution. For a link, go to www.national geographic.com/media/ngm/9808/berger/. The fossil record has grown exponentially since Charles Darwin called it "paltry" but scientists are still trying to assemble broad theories from small piles of bones. Berger (above) thinks South Africa's unexplored terrain can help fill some gaps."We're digging a lot of new sites that have fantastic fossils." REDRAWING OUR FAMILY TREE?