Discovery Of Bone, Tooth Fossils Bites Into Theories Of Evolution

The Second Front Page

July 12, 2001|By Robert Cooke, Newsday

A new discovery of bones and teeth in an arid region of Ethiopia may reach back more than 5 million years, almost to the time when humans and chimpanzees shared a common ancestor, scientists said Wednesday.

The evidence also suggests our hominid forebears evolved in wooded, wet territory, rather than on open, dry grasslands. If so, this may force a rethinking of ideas about human evolution as it occurred in eastern Africa.

In reports to be published today in the journal Nature, paleoanthropologists announced the discovery of 5.5 million-year-old fossils in the rugged, dry Awash region of Ethiopia. These fossils apparently came from a pre-human creature that walked upright.

The species lived near the time when humans and chimps diverged, the chimps adopting knuckle-walking posture, and humans remaining upright, bipedal. And the place where they lived seems to have been woodland, not savanna.

According to evolutionary biologist Tim White and his colleagues, the new fossil finds "provide fresh perspectives on hominid origins and early evolution." As they wrote in Nature, the evidence shows "these earliest hominids derive from relatively wet and wooded environments" that were being molded by changing local climate, volcanoes and earthquakes.

If their assessment is correct, White and his seven colleagues wrote, "these findings require fundamental reassessment of models" of human origins that have relied on climate change and grasslands to drive evolutionary change. A common theory is that the disappearance of forests forced pre-human creatures to walk upright on their hind legs.

One of White's co-workers at the University of California, Berkeley, Yohannes Haille-Selassie, discovered the fossils. He announced in a separate Nature paper that the evidence also suggests this pre-human creature was "close to the common ancestor of chimpanzees and humans."

Unfortunately, no fossilized remains of chimpanzees are known, the scientists said, so it is difficult to trace relationships along the chimpanzee line to that common ancestor. It has been suggested that chimpanzee fossils are so scarce because the animals lived in wetter areas, where bones tend to decay rapidly and disappear.

According to Henry Gee, an editor at Nature, "most researchers agree that the most recent common ancestor of humans and chimpanzees lived about 5 million to 6 million years ago." Conceivably, some of the fossils identified as pre-human could be pre-chimpanzee, he said, or they could be from an extinct offshoot, "a cousin of the latest common ancestor."

The researchers said the new finds also raise questions about bipedality -- walking upright on two legs -- and whether that is actually a sign of being in the human line.

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