Science: Redrawing the Family Tree

Now that's a big monkey, thought Paleontologist Alan Walker as he plucked the skull fragment from a gully west of Kenya's Lake Turkana. But that was no monkey. The bone belonged to a 2.5 million-year-old ape-man called Australopithecus boisei. The discovery surprised Walker, since he and most anthropologists believed the boisei species had evolved 2.2 million years ago. "This is probably more significant than almost anything we've had for a good number of years," says Anthropologist Richard Leakey, one of Walker's coauthors of a report about the fossil in last week's issue of Nature. Leakey's excitement is understandable: the find casts...