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This wasn't just tool use; it was technology. Explains archaeologist Sileshi Semaw, a postdoctoral researcher at Indiana University in Bloomington, who helped find a huge cache of 2.6 million-year-old tools at Gona in the early 1990s: "The Gona hominids [carefully] selected workable raw materials." Since there are no local sources of such materials at Bouri, where the A. garhi fossils were found, the hominids must have carried their tools with them when they traveled there.
Did A. garhi make both the tools Semaw found and the ones used to butcher animals at Bouri? "If it wasn't garhi," asks White, "what would it have been?" Semaw is more cautious. "Australopithecus garhi is the best candidate thus far," he concedes, but he doesn't rule out the possibility that another species, yet undiscovered, deserves the credit.
Whoever did it, the creation of technology gave its inventors an astonishing advantage over other hominid species. Stone hammers and blades let them exploit carcasses left behind by other predators and permitted them to shift to an energy-rich, high-fat diet. "That," asserts Asfaw, "leads to all kinds of evolutionary consequences."
One of these, White suggests, was the ability to exploit a broader range of habitats, eventually enabling our ancestors to leave Africa and colonize most of the globe. But even more important was the expansion of our brain, with all the potential that went with it. Explains Meave Leakey: "The brain is a very expensive organ in terms of metabolism." It can grow larger only in a species that's routinely consuming high-energy food. One impetus for such growth--and in particular, the growth of the cognitive areas that distinguish ours from other large brains--could have come from our increasingly creative use of tools. Still, the ultimate use to which those big, sophisticated brains would be put would not appear for many hundreds of thousands of years.
MODERN HUMANS
Just as australopithecus afarensis eventually gave rise to the genus Homo, so one species came to stand out among the Homo line and eventually led to modern humans. The fossil record is far too spotty to say how Homo habilis (handy man) and other members of its genus--H. rudolfensis, H. ergaster and H. erectus--were related, to what extent they overlapped or even whether they all represent distinct species. Many scientists believe, though, that it was H. erectus that was the ultimate victor, the direct ancestor of our own species.
H. erectus was also the first hominid to emigrate from Africa, at least 1.8 million years ago, spreading all the way to China and Indonesia. Then, at some point--for reasons still mysterious--the lineage diverged, with one branch leading to Neanderthals and another to modern humans.
Exactly when and how it happened is unclear. The oldest Neanderthal fossils in hand date only to 200,000 B.P., and the oldest Homo sapiens to about 100,000. But some recent discoveries may help answer those questions. A 1 million-year-old cranium from Buia, Eritrea, for example, has characteristics of both H. erectus and H. sapiens. And what Asfaw and his colleagues call a "spectacular" partial cranium of the same age from Ethiopia should help as well when it's formally unveiled.