UC Berkeley Grad Student Uncovers Link in Human Evolution in Ethiopia

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The murky history of humankind's ancestry has been illuminated by the work of a team of scientists that includes UC Berkeley researchers.

Henry Gilbert, a UC Berkeley integrative biology graduate student, discovered a one-million-year-old Homo erectus cranium, providing new evidence that the Asian Homo erectus and the African Homo ergaster, extinct relatives of modern humans, actually belong to one coherent species.

The research hit the cover of the journal Nature today.

Other authors of the publication include UC Berkeley integrative biology professor Tim White and scientists from universities and laboratories throughout the country. The principal author was Berhane Asfaw, a prominent Ethiopian researcher.

Scientists have long debated the evolutionary history of humans, and these researchers' findings will support a newer theory about humankind's ancestors.

One theory among paleontologists is that Homo erectus can be split into two distinct species, based on physical characteristics, as far back as 1.8 million years ago, said White. The new discovery provides evidence to the contrary.

The specimen found in Ethiopia is only one million years old, and based on previous findings, some paleontologists would have expected it to clearly show physical characteristics of Homo ergaster because it was found in Africa. But instead, the cranium resembles Homo erectus, previously thought to be of exclusively Asian lineage.

"(The cranium) looks like Asian Homo erectus," Gilbert said. "It's well within the range of variation you'd expect to see within a single widely distributed species."

The idea was that African and Asian specimens represent two divergent lineages, distinguishable from each other at the species level by morphology. If this were true, a quantitative analysis of physical characteristics in all existing specimens should have partitioned them into two distinct groups, by

geography as well as morphology, White said.

White said he was already skeptical of this view, because the only evidence available from one million years ago in Africa was one fragmentary cranium.

Once the new fossil was included in the quantitative analysis, there was no clear division between African versus Asian in the one million year old crania, White said.

"Now we have this cranium from Africa that is not distinguished at the species level from the Asian forms," White said.

White does not expect that this development will be universally accepted.

"It will be controversial, but that's not a bad thing," White said.

The discovery represents a valuable link in the evolutionary history of modern humans because it falls in between previously discovered specimens not only in time, but in anatomical development as well, White said.

Since this discovery fills out the fossil record, it strengthens the argument for human evolution, as opposed to creationism, White said.

In 1997, Gilbert found the Homo erectus calvarium, or the upper part of a skull which lacks a lower face and teeth. The skull was embedded in the sediment of the Middle Awash study area in Ethiopia, about 140 miles northeast of Addis Ababa, the capital city.

The fossil was slightly exposed, and immediately recognizable as part of a skull, Gilbert said, calling the discovery of the Homo erectus cranium-the fourth one found in Africa-"breathtaking."

"You see something like that and you know it's going to be important," Gilbert said.

It took two to three years of careful scraping with dental tools and porcupine quills to remove the sedimented stone from the fossil, which remains in Ethiopia as a national treasure, Gilbert said.

Preliminary analysis and main description of the calvarium commenced about one and a half years ago. Although a lengthy process, the project was a high priority, Gilbert said.


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