Berkeley Researchers Head Team That Discovers New Species of Human Ancestor
Earliest Evidence of Meat-Eating, Early Beings Has Been Unearthed in Ethiopia
Posted April 28, 1999
In last week's issue of the journal Science, Ethiopian anthropologist Dr. Berhane Asfaw and colleagues from the United States and Japan describe fossils of what may be a direct human ancestor and an evolutionary link between the ape-man of Africa, Australopithecus, and the genus Homo.
In a companion paper, other members of the research team, including Berkeley archaeologist J. Desmond Clark, announce evidence that antelopes and horses were butchered with the world's earliest stone tools.
Berkeley professor of integrative biology Tim White also led the research team. In 1992, his same research team found Ardipithecus, the earliest known hominid, at the nearby Middle Awash site of Aramis.
Altogether, the interdisciplinary research team involves archaeologists, geologists and paleontologists from about 40 different institutions in 13 different countries.
Although "we cannot yet conclusively link the new species with the butchery or the more modern limb proportions," said White, he and other scientists say the new discoveries are important for three reasons. First, they add a new potential ancestor to the human family tree. They also show that the thigh bone (femur) had elongated by 2.5 million years ago, a million years before the forearm shortened, to create our familiar human proportions.
Finally, evidence of large mammal butchery shows that the earliest stone technologies were aimed at getting meat and marrow from large mammals. This signals a dietary revolution that may have eventually paved the way toward an invasion of new habitats and continents.
Theories abound in the contentious field of human origins research, but a basic outline has emerged from genetic and anatomical studies of modern apes and humans. Fossils found over the last 75 years in Africa have validated and extended this picture.
More than five million years ago, the evolutionary lines leading to humans and the African chimpanzees and gorillas split. Research in Africa since the 1920s has identified several successive fossil species leading to humans. As more fossils have been found, the family tree has become more complex, sprouting several side branches including the Australopithecus "ape-men" of southern and eastern Africa.
The earliest known fossil hominids belong to the genus Ardipithecus and date to 4.4 million years ago. The descendent ape-man genus Australopithecus was first recognized in South Africa in the 1920s. Several species are now known. Some, like A. aethiopicus (the "black skull" at 2.6 million years ago) specialized and went extinct.
Other earlier forms like the "Lucy" species Australopithecus afarensis (3.6 to 2.9 million years ago) were less specialized and therefore suitable ancestors of the earliest generally recognized species in our own genus, Homo. That species, Homo habilis, is widely recognized as the maker of the earliest stone tools some 1.8 million years ago.
Some researchers think that "Homo habilis" fossils actually represent two different species. But the relationships between the earlier ape-men (particularly A. africanus) and their stone-tool-wielding early Homo descendants have been impossible to decipher because of the lack of an adequate east African fossil record between 2 million and 3 million years ago.
The new Ethiopian fossils reported this week help fill this gap. According to Asfaw, the Ethiopian co-leader of the team, they are certain to stimulate new debate and additional research.
The discoveries, made between 1996 and last December, come from an area in the Afar desert of Ethiopia. They refocus attention on the eastern part of Africa, a crucible of human evolution, according to White.
When scientists carefully removed the newly-discovered specimen, they were shocked to find a combination of bony and dental features completely unforeseen and unanticipated. They named it Australopithecus garhi. The word "garhi" means "surprise" in the Afar language.
The new species joins a growing gallery of ancestors that has emerged from Africa in the last 30 years. Scientists are currently split over how many branches of early hominids existed.
The published paper provides several alternative family trees, but Asfaw and colleagues conclude that it is too early to choose. They say that identifying A. garhi as a new species is just the first step in solving the puzzle and that more fossils will be needed to choose the most accurate tree -- and to reveal whether human evolution between 2 million and 3 million years ago was "jerky" or relatively smooth.
The scientists say it is possible that A. garhi was the direct ancestor of Homo, including modern humans.
Meat and Marrow Eating
Ethiopian archaeologist Sileshi Semaw (now at Indiana University) announced two years ago that he had found the world's earliest stone tools at 2.5 million years at a site immediately north of the Middle Awash. He and his colleagues could only speculate about which human ancestor made these tools and what they were used for. The Middle Awash discoveries now answer that question. At the same time, they identify Australopithecus garhi as the best candidate for toolmaker.
The scientists say this new evidence indicates a very early breakthrough in the human career. Methods of acquiring large quantities of a high-quality diet (meat and marrow fat) were important because they would greatly improve our ancestors' ability to provide for themselves and their offspring.
"The development of stone tool technology allowed this dietary revolution," said White. "This is the earliest evidence of a key adaptation that let our ancestors spread beyond Africa."