Early human bipedalism confirmed

John Gurche and Brian Richmond

The shape of a fossil thigh bone (center) from Kenya shows that our early ancestors had already evolved upright walking by 6 million years ago.

Sometime between 8 million and 5 million years ago, an evolutionary divide occurred: Some apes left the trees behind and adopted an upright form of walking. The two-legged, or bipedal, population formed the basis of the hominin lineage that gave rise to Homo sapiens and its close ancestors. To find evidence of the earliest human ancestors, scientists scrutinize fossils from around this time period.

One such fossil, a 6-million-year-old thigh bone from a species called Orrorin tugenensis, is the topic of a new study published in Science March 20. Despite previous examinations of this fossil, which was discovered in Kenya in 2000, researchers still debate whether O. tugenensis walked upright and whether it was more closely related to the australopithecines that lived 3 million to 2 million years ago or to the much later Homo.

Brian G. Richmond of George Washington University in Washington, D.C., and William L. Jungers of Stony Brook University in New York say that they have resolved the debate by determining that O. tugenensis did indeed walk upright and that its hip structure is more similar to that of the australopithecines.

Chris Parendo
Geotimes contributing writer

This story originally appeared on Geotimes online on March 21, 2008. Read the complete story in the Geotimes Web Extra Archive at www.geotimes.org/WebextraArchive.html.

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