The "Gang" Hits Again

Like other members of the famous "hominid gang," the sharp-eyed fossil hunters employed by paleontology's Leakey family, Justus Erus spends three months a year scouring the dry, bone-rich riverbeds around Lake Turkana, in northern Kenya. It is a scrubby, desolate landscape, where the people are desperately poor and gun-toting young men are a menacing presence. But it is hallowed ground to scientists because of the clues it offers to early human history. Still, even after five years, Erus, a 30-year-old Turkana tribesman, had scored nary a hit--just bits of ancient animal bones and teeth.

Then one scorching morning during the final week of the gang's explorations in August 1999, at a site called Lomekwi, Erus noticed a white object, just an inch or so across, sticking out of a patch of brown mudstone. "I thought maybe it was [the bones of] a monkey," he says. Beckoning the expedition's co-leader, Meave Leakey, wife and daughter-in-law, respectively, of Richard and Louis Leakey and renowned in her own right, he asked her opinion. By nightfall they realized that they had uncovered the partial remains of a humanlike skull.

The fossil turned out to be a totally new prehuman species and last week re-ignited one of paleontology's greatest debates: Did we evolve in direct steps from a common apelike ancestor between 6 million and 4 million years ago? Or did the human family tree sprout several branches, some of which petered out?

In the past 20 years the Leakeys and others have dug up overwhelming evidence showing that between 2.5 million and 1 million years ago, the then lush woodlands and savannas of eastern Africa--where our family tree first took root--were the habitat of rival species, most of which were evolutionary dead ends. But what about before that? Paleontologists have generally agreed that there was just one hominid line, beginning with a small, upright-walking species known as Australopithecus afarensis, most famously represented by "Lucy," a remarkably complete (about 40%) skeleton found in Ethiopia in 1974.

Now that view is being challenged. The new skull, described by Leakey and six colleagues, including her and Richard's daughter Louise, 29, in Nature last week, pushes the presence of coexisting species back another million years, to between 3.5 million and 3.2 million years ago. That's right in Lucy's time. Yet it is so different from Lucy that they assign their fossil, which they call Kenyanthropus platyops, or "flat-faced man of Kenya," to a new genus, or grouping of species. "This means we will have to rethink the early past of hominid evolution," says Meave Leakey, head of paleontology at the National Museums of Kenya. "It's clear the picture isn't as simple as we had thought." Even Lucy's discoverer, Donald Johanson, director of the Institute of Human Origins at Arizona State University, concurs. "This is a reminder that there are probably a lot more species out there," he says.

K. platyops not only had a much flatter face than Lucy, she also had smaller teeth. From the teeth, the scientists conclude that it probably ate fruits, berries and small insects while A. afarensis consumed tougher vegetation like roots and grasses. "They were unlikely to compete," says team member Fred Spoor of University College London. "Two species usually don't occupy the same ecological niche."

Old flat-face could displace A. afarensis as a direct link in the human lineage. Or it may be part of a branch leading to Homo rudolfensis, a species with a strikingly similar face that lived in East Africa between 2.4 million and 1.8 million years ago. "You find something beautiful and new, but the conclusion is you actually know less," says Spoor. "But we're getting there."