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But figuring out how they arose, how they were related and what they evolved into--those that weren't evolutionary dead ends--has proved elusive. Not only is the fossil record full of holes, but the hominid species from eastern Africa haven't shown up in southern Africa, and vice versa. A remarkably preserved skeleton found in South Africa's Sterkfontein cave could change all that. Believed to be at least 3.3 million years old, the bones may belong to A. afarensis, making it the first of Lucy's species uncovered in that area. But the skeleton hasn't been fully excavated yet, and its discoverer, Ron Clarke of the University of the Witwatersrand, in Johannesburg, thinks it may represent yet another previously unknown species.
Whatever the evolutionary relationships between these prehuman species, paleoanthropologists know that at some point a second major shift took place. One of Lucy's descendants gave rise to a new kind of creature, the first of the genus Homo. Yet none of the known variants of Australopithecus seemed anatomically close enough to the Homo line to qualify.
Then, four months ago, Asfaw and White's team made another dramatic announcement. A fragmentary skull found near Bouri, an Ethiopian village in the Middle Awash region northeast of Addis Ababa, could well be from the missing australopithecine that sired the human race (see cover photo). Excavated in 1997, its jutting face and upper jaw filled with large teeth clearly belong to a species more advanced than A. afarensis yet more primitive than the earliest humans.
The mix of characteristics wasn't precisely what the experts expected--they were looking to see smaller, more specialized teeth and a larger braincase. So they named their hominid Australopithecus garhi (garhi means surprise in Afar). But the skull's intermediate anatomy and its age--about 2.5 million years--put it midway in both time and form between the most recent A. afarensis and the oldest known fossils of our own genus.
That alone would make A. garhi a prime candidate for the long-sought evolutionary link between Lucy's species and the first humans. But the researchers also found that nearby animal bones dating from the same period had been butchered with stone implements. Cut marks on one antelope jawbone suggest that the hominids used a sharp stone flake to remove the animal's tongue. The leg bone of another animal is scarred by cuts, chop marks and signs of hammering, evidence that it was scraped clean of meat and bashed open to expose the nutritious marrow.
Earlier discoveries at Gona, an Ethiopian site about 60 miles north of Bouri, had already shown that someone was using carefully manufactured stone tools in the area at about that time. Now Asfaw and White's team could make a circumstantial case that their species, A. garhi, was the gifted toolmaker. If so, this was a crucial bit of scientific sleuthing. In the 2 million years since the first human ancestor began to walk upright, nothing much had changed. Now something had. Rather than just using sticks and stones to leverage innate abilities--something done by plenty of animals, from chimps to otters to finches--someone had deliberately selected and modified specific raw materials in a sophisticated and consistent way, and with careful intent.