Researcher Settles Debate Over Early Human Origins: Fossils Show Upright Walking as Early as Six Million Years Ago (3/24/2008)

Researcher Settles Debate Over Early Human Origins; Fossils Show Upright Walking as Early as Six Million Years Ago

George Washington University Professor Brian Richmond and Stony Brook University Professor William Jungers have discovered that humans' early ancestors were adapted to walking upright on two legs almost six million years ago, settling scientific debate over fossils discovered in 2000. This finding shows that the fossils belong to very early human ancestors and that upright walking is one of the first human characteristics to appear in our lineage, just after the split between human and chimpanzee lineages.

The research is the first thorough analysis of the Orrorin tugenensis fossil -- a fragmentary piece of femur (thigh bone) -- which was discovered in Kenya in 2000 by a French research team. Richmond, associate professor of anthropology and a member of GW's Center for the Advanced Study of Hominid Paleobiology, and William Jungers, professor of anatomical sciences at Stony Brook University, conducted the study. The findings are published in the March 21 issue of the journal Science.

Until this analysis, scientists have engaged in debate over the fossil's significance. The fossil's age, almost six million years old, falls within the timeline (five to eight million years ago) of when genetic differences indicate that chimpanzees and humans had a common ancestor.

"This research solidifies the evidence that the human lineage split off as far back as six million years ago, that we share ancestry with Orrorin, and that our ancestors were walking upright at that time," said Richmond. "These answers were not clear before this analysis."

Jungers, co-author of the research, said, "The challenge ahead is to identify what precipitated the change from this ancient and successful adaptive theme to one more similar to our own."

The analysis of Orrorin tugenensis' bones show that the early human ancestor combined upright walking with tree climbing, a way of life that seemed to persist for about four million years. Only with the emergence of certain early members of our genus, Homo, around two million years ago, do scientists see the skeleton organized into a more human form, such as longer legs for distance walking and running, large hip joints, straight finger and toe bones, and bigger brains.

Note: This story has been adapted from a news release issued by George Washington University

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