SAY WHAT THEY WILL ABOUT THE importance of brains in research, in anthropology there's no substitute for sharp eyes and an easily stubbed toe. One afternoon in 1992, while a team of scientists laboriously sieved soil in the harshly beautiful Ethiopian valley, their Afar-tribe assistants combed a nearby hill. Suddenly, one of the Afar appeared on the crest waving and shouting. The histrionics meant only one thing: he had stumbled upon the grayish-white jawbone of a hominid, an almost-human of whom we are the direct descendants. It took an additional 20 months to excavate and piece together what turned out to be more than 200 rock-frosted fragments, but the anthropologists are finally announcing what inspired the euphoria: the first skull of the oldest known member of the human family. The fossil, predicts paleontologist Leslie Aiello of University College, London, could help "settle some of the most heated controversies surrounding ... the human lineage."
One of those debates has been just how many roots anchor our family tree. The new fossil belongs to the same species as 3.18 million-year-old Lucy, the slender little female discovered a mile away in 1974. Called Australopithecus afarensis, she was the first of what now amounts to more than 300 fossils from 75 individuals. But the skeletons seem so different-some as lithe as a ballerina and others as brawny as a fullback, some that seemed like simian tree climbers and others that walked fully erect-that some scientists argued they represent two species. The latest find-call him Son of Lucy-supports the notion that these fossils, 3 million to 3.9 million years old. are all afarensis, argue the anthropologists in the current issue of the journal Nature. it was the first species to evolve after the human and ape lineages split. By the evidence of their teeth, afarensis ate fruit, insects and small animals. They left no tools but may have used sticks as today's chimps do to scoop termites out of nests.
Son of Lucy should also resolve what afarensis looked like and how they got around. He has a protruding jaw, thick brow ridges and a braincase so small it leaves no doubt that our ancestors learned to walk long before they mastered complex thought. The women topped out at four feet and 75 pounds, but their consorts grew to five feet and 100 pounds. And the arm bones of the new 3 million-year-old man suggest afarensis was as comfortable scrambling around trees as walking upright on the ground.
The new fossil is startlingly similar to the oldest afarensis. For almost 1 million years afarensis hardly changed, says Donald Johanson of the Institute of Human Origins, codiscoverer of Lucy as well as the new fossil. "Afarensis was a very flexible species," adds IHO paleontologist William Kimbel. "Even as the local climate changed from humid to arid and back-a change that made other animals go extinct-this little hominid adapted by learning how to use the new flora." Yet in the blink of an evolutionary eye, 3 million years ago, afarensis gave rise to no fewer than five branches of the human family tree. Two led to brainy, tool-using Homo; three, to brawny australopithecines that went extinct. When the IHO scientists return to Ethiopia this year, they hope to stub a toe on a human fossil from 2.5 million to 3 million years old. Such a find could fill in the gap between afarensis and the first Homo species. Get ready for Lucy's grandchild.