College of LAS « Illinois

Anthropology

Origin of Bipedalism Tied to Environmental Changes

A person holding up some bones

Paleoanthropologists discover why prehumans stood up on two feet.

During the past 100 years, scientists have tossed around a great many hypotheses about the evolutionary route to bipedalism, and what inspired our prehuman ancestors to stand up straight and amble off on two feet.

Now, after an extensive study of evolutionary, anatomical and fossil evidence, a team of paleoanthropologists from UI, the University of Toronto, and the New York College of Osteopathic Medicine has narrowed down the number of tenable hypotheses to explain the origin of bipedalism and our prehuman ancestors' method of navigating their world before they began walking upright.

The hypothesis they found the most support for regarding the origin of bipedalism is the one that argues our ancestors began walking upright largely in response to environmental changes—in particular, to the growing incidence of open spaces and the way that changed the distribution of food.

In response to periods of cooling and drying, which thinned out dense forests and produced "mosaics" of forests, woodlands and grasslands, it seems likely that "some apes maintained a forest-oriented adaptation, while others may have begun to exploit forest margins and grassy woodlands," says LAS paleoanthropologist Brian Richmond, lead author in the new study. The process of increasing commitment to bipediality probably involved "an extended and complex opening of habitats, rather than a single, abrupt transition from dense forest to open savanna," he says. "Evidence from the wrist joint suggests that the earliest humans evolved bipedalism from an ancestor adapted for knuckle-walking on the ground and climbing in trees."

Spring 2003