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Fossil discovery causes evolution stir

SHARE Fossil discovery causes evolution stir

A team of scientists led by an anthropologist from the University of California at Berkeley has discovered the fossilized remains of what they believe is humanity's earliest known ancestor, a creature that walked the highlands of East Africa nearly 6 million years ago.

The discovery is already challenging older theories about the ancestral lineage of humans and changing scientific views of the environment that fostered the evolution of prehumans as they moved from verdant forests to open grasslands.

The team reporting the discoveries Thursday was led by two Ethiopian scholars: one an anthropologist still working on his doctorate at the University of California at Berkeley, the other a geologist now at UC's Los Alamos National Laboratory in New Mexico.

The fossils were gathered during four years of exhausting expeditions to a harsh and hostile Ethiopian desert where lions and cheetahs hunt at night and few humans roam the wilderness by day.

The remains include a jawbone and its teeth, hand bones and foot bones, fragments of arms, a piece of collarbone and — most important — a single toe bone whose form provides strong evidence that the prehuman creatures walked upright, the scientists said.

The toe bone, in fact, is a crucial clue to the earliest days of human evolution that developed soon after the ancestral lines of apes and humans split apart — perhaps 6 million to 8 million years ago.

Two papers on the discovery by the Ethiopian scientists are appearing in the journal Nature Thursday — one by Yohannes Haile-Selassie, a doctoral candidate at UC Berkeley, the other by Giday WoldeGabriel of Los Alamos, together with colleagues in the United States and Ethiopia.

Dating of the fossils, using the known decay times of radioactive argon sequestered in the fossils as a kind of atomic clock, was accomplished by Paul R. Renne of the Berkeley Geochronology Center.