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Thursday, March 21, 2002

The skull fragment shows massive brow ridges and the long, low vault characteristic of Homo erectus. The entire cranial base is preserved, and the specimen reveals a great deal of anatomical detail which allowed the investigators to infer its close evolutionary relationships to similar fossils in Java, China, Georgia, and Italy.Photo copyright by David L. Brill \ Brill Atlanta

Lab researcher participates in homo erectus skull discovery

Laboratory geologist Giday WoldeGabriel again has played a role in a major anthropological discovery - this one involving Homo erectus, an precursor of modern man that is believed to have roamed the earth between one and two million years ago.

Working with paleoanthropologist Tim White of the University of California at Berkeley, WoldeGabriel and an international research team unearthed fragments of a skull belonging to a member of the Homo erectus species from ancient sediment layers in Ethiopia. The skull indicates that Homo erectus populated Europe, Asia and Africa, and that species counterparts on each of those continents were the same - a finding highlighted today in a cover story in the journal Nature.

Previously, some anthropologists had argued that Homo erectus fossils found in Asia represented a different species from the fossils of Homo erectus’ contemporaries found in Africa and Europe, which had been named Homo ergaster.

White’s team’s newest fossil discovery from Ethiopia indicates that Homo erectus was one species that populated all three continents.

“This fossil is a crucial piece of evidence showing that the splitting of Homo erectus into two species is not justified,” said White. “This African fossil is so similar to its Asian contemporaries that it’s clear Homo erectus was a truly successful, widespread species throughout the Old World.”

The research team also asserts in the Nature paper that the onset of the ice ages about 950,000 years ago led to divergent evolution among Homo erectus - with the African population most likely evolving into modern Homo sapiens, the European branch probably evolving into Homo neanderthalensis, or Neanderthals, and the Asian population becoming extinct.

Prior to the team’s find, anthropologists had given different names to other Homo erectus discoveries, for instance calling them Peking Man or Java Man.

“What we are saying in this paper is that the anthropological splitting common today is giving the wrong impression about the biology of these early human ancestors,” White said. “The different names indicate an apparent diversity that is not real. Homo erectus is a biologically successful organism, not a whole series of different human ancestors, all but one of which went extinct.”

Although the team found the fossil fragments in 1997, it took team members more than two years to reassemble the pieces into a nearly complete skull.

Of vital importance in any of these fossil discoveries is the ability to accurately understand the temporal and spatial settings of the specimens in the field. WoldeGabriel’s geological expertise in this area is invaluable. Using sediment layers that contain the fossil remains, WoldeGabriel, of Hydrology, Geochemistry and Geology (EES-6), has been able to successfully assess the geological history and environment of the fossils.

WoldeGabriel’s expertise in understanding the basin geology gave him the ability to characterize the environment in which our earliest human ancestors lived. In Homo erectus’ time a million years ago, the Middle Awash was an expansive grassland inhabited by a number of animals, including antelope, elephants, baboons and hyenas; in fact, marks on the fossilized skull indicate that the Homo erectus specimen may have been gnawed on by hyenas or other animals after it died.

The latest fossils are about a million years old, making it a Homo erectus specimen much younger than the Asian and European discoveries -believed to be about 1.8 million years old.

The area where the nearly complete Homo erectus skull was found is located in the Middle Awash region of Ethiopia. The area is within the Afar rift system and is rich in fossil-bearing sediments. The area is familiar to the research team, which has made several discoveries in the past.

WoldeGabriel said working with the team is exciting and rewarding. However, work in the study area never ends with a single find.

“Once you find something in an area, you can’t just quit,” WoldeGabriel said. “You have to keep going back. Each rainy season unearths other fossils, so you have to keep checking an area every year with every expedition.”

As such, each successive discovery reduces the amount of free time that team members have to search for new sediment beds that may contain fossils of as-yet-undiscoverd species.

Last summer, WoldeGabriel and researcher Yohannes Haile-Selassie of UC, Berkeley made scientific headlines when they announced the discovery of Ardipithecus ramidus kadabba, a creature who lived between 5.2 and 5.8 million years ago. The fossils are believed to be those of the oldest human ancestor discovered to date.

WoldeGabriel says he believes the Middle Awash study area where he and the team explores each year eventually could produce the “Holy Grail” of paleoanthropolgical discoveries: The so-called “Missing Link” - the split in the evolutionary tree between chimpanzees and humans. Those elusive fossils have yet to be found and may never be found. But to WoldeGabriel, the search continues.

“I plan to continue to go back as long as I can,” he said.

Funding for WoldeGabriel’s work in Ethiopia comes from Los Alamos’ Institute of Geophysics and Planetary Physics.

For more information on the most recent paper in Nature, see the UC Berkeley news release.

--James E. Rickman

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