April 13, 2006

Fossil Find Strengthens Sequence of Human Evolution

Location of the discovery explains an early separation of hominid species

By SETH BORENSTEIN
Associated Press

WASHINGTON - Fossils have long provided snapshots of the human family tree, but a new find in Africa gives scientists a kind of mini home movie showing man's primal development.

Because the 4.2-million-year-old fossil is from the same human ancestral hot spot in Ethiopia as remains from seven other human-like species, scientists can now fill in the gaps for the most complete evolutionary chain so far.

"We just found the chain of evolution, the continuity through time," said Ethiopian anthropologist Berhane Asfaw, co-author of the study being reported today in the journal Nature. "One form evolved to another. This is evidence of evolution in one place through time." <>The species, Australopithecus anamensis, is not new, but its location is what helps explain the giant leap from one early phase of human-like development to the next, scientists say. All eight species were found in a region called the Middle Awash.

"It's like 12 frames of a home movie, but a home movie covering 6 million years," said study lead author Tim White, co-director of Human Evolution Research Center at University of California at Berkeley. Fossils in the region cover three major phases of human development.

"The key here is the sequences," White said. "It's about a mile thickness of rocks in the Middle Awash, and in it we can see all three phases of human evolution."

Modern man belongs to the genus Homo, a subgroup in the family of hominids. What evolved into Homo was likely the genus Australopithecus, which includes the famed 3.2 million-year-old "Lucy" fossil found three decades ago.

A key candidate for the genus that evolved into Australopithecus is called Ardipithecus. The finding is important in bridging but not completely the gap between Australopithecus and Ardipithecus.

In 1994, a 4.4 million-year-old partial skeleton of the species Ardipithecus ramidus the most recent Ardipithecus species was found about six miles from the latest discovery.

"This appears to be the link between Australopithecus and Ardipithecus as two different species," White said.

The major noticeable difference between the phases of man can be seen in Australopithecus' bigger chewing teeth to eat harder food, he said.


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