A GW scientist concluded that a six million year-old Kenyan fossil is the oldest human relative to have walked upright and on two feet.

GW associate anthropology professor Brian Richmond and SUNY Stony Brook professor William Jungers conducted measurements of a the thigh bone of an Orrorin tugenesis fossil, which a French research team found in 2000. The findings were published in the March 21 issue of Science magazine.

The fossil is the earliest evidence of bipedalism and “the oldest evidence tracing the lineage of human ancestors,” Richmond said.

He added, “My research interests have always been human origins and the origins of human adaptations, and so when this discovery was first announced in 2000, it was pretty clear that this was going to be an important discovery.”

Richmond analyzed the bone sizes and compared it to other fossils. This finding reinforces the idea that the split between human and apes occurred sometime between five and eight million years ago. Walking upright and on two feet is a crucial characteristic distinguishing humans from apes. This particular ancestor may have climbed trees as well as walked on two feet.

The researchers plan to scan the inside of the bone to better understand the characteristics of the primitive human. Richmond and Jungers also plan to conduct research on the environment during Orrorin tugensis’ time to better understand the reasons for the development of walking on two feet, he said.

“We know bipedality is the key trait that separates humans from apes,” said Robin Bernstein, an anthropology professor.

But to some researchers, the 6 million-year-old fossil is only evidence that apes, not humans, in that period walked on two feet.

“For myself, it’s quite interesting because if you look at the other fragments, most of those bits and pieces would not make you think this is a human ancestor; it would make you think it was an ape,” said GW human origins professor Bernard Wood. “To me, it suggests that bipedality may not have been confined to our lineage. It may have been something that extinct apes were doing.”

Orrorin’s place in the human family tree is still unclear, and Wood said more research is necessary to show the relationship between humans and Orrorin.

“If you want to show if it’s one of our direct ancestors, you’ve got to go and find more of it,” he said.

James Clark, chair of the biology department, called the study an “important interpretation,” and said he “did not see any big red flags” when he was reading the report.

“It’s not earth-shattering . it basically extends things back in time.” he said.