In the arid badlands of Ethiopia, researchers have uncovered evidence that humanity’s direct ancestors used tools 2.33 million years ago, offering a new clue to a crucial hidden chapter of human development, the Berkeley, Calif.-based archaeologists announced today.
Two local Afar tribesmen working for the Institute of Human Origins discovered pieces of a primitive human jaw in the Hadar region of Ethiopia that belong to the genus Homo - the family that includes all modern humanity - amid a collection of crude stone tools and other fossil mammal bones.
The new find offers a rare look into one of the most mysterious periods of human development - the time when dramatic shifts in the climate of Africa may have spurred the evolution of modern humanity from its more primitive ancestors. Almost nothing is known about this period when the human family of species first appeared.
“This is very important,” said F. Clark Howell, a noted authority on early human origins at the University of California at Berkeley. “This opens a whole new window into a time when we think Homo is emerging, and that is very exciting.”
Experts said the discovery appears to be one of the oldest known specimens of the root stock of humankind. Only one other Homo fossil of such antiquity is known to exist.
An international team of 16 scientists described the new finds in the December issue of Journal of Human Evolution.
The fossil jaw is at least 400,000 years older than other more complete collection of fossils belonging to the Homo lineage, institute science director William H. Kimble said. At the same time, it also is about 700,000 years younger than a more primitive pre-human species that also lived in the area.
“The critical thing here is that the earliest good record of our own lineage begins only about 2 million years ago,” Kimble said. “Before that, the record of Homo is pitiable. We are trying to fill in some voids.”
Especially provocative, the researchers said, is the fact that the fossil was discovered near ancient tools. Scattered near the jaw fragments were 20 stone flakes and several “chopping tools” fashioned from chipped river cobbles, the researchers said. When they excavated, they found another 14 stone artifacts.
There is no direct way to prove the individual whose bones were found among the tools made or used them, but together they represent the oldest known, firmly dated association of stone tools with a fossil human ancestor, the scientists said.
“It was one of the most wonderful surprises,” said Donald C. Johanson, president of the private institute that made the find public Tuesday. “It is the oldest known association of our own genus with primitive stone tools.”
Other researchers, however, reserved judgment on the significance of the discovery.
“It has been known for a long time that stone tools exist at this time,” said Andrew Hill, a Yale University anthropologist involved in discovering the other known Homo fossil from this period. “It depends on what conclusions you draw from the association with tools. It is interesting but it is very difficult to say what it tells you.”
The chipped stones all bear many of the same characteristics of early human manufacture that are typical of tools found in Tanzania, Kenya and Ethiopia, which date from 1.8 million years and 2.35 million years ago. No one knows what species made them.
The researchers are not sure to which primitive human species the fossil belongs, leaving open the possibility that the jaw could be evidence of a previously unknown branch of the human family tree.
In many ways, Kimble said, the teeth and jaw bones resemble those belonging to more modern human species, such as Homo habilis, but there is not enough fossil material on hand to assign it to a known species, he said.
“The basis for the caution is that there are a few similarities (to known species) but they are by no means overwhelming,” Kimble said. “Because of the time between the next-oldest fossil specimens - at least 400,00 years - we are awaiting additional evidence before we make a judgment.”