OUR early ancestors had the edge over us when it came to efficient walking. An anthropologist in Washington state has modelled the action of an australopithecine, one of the ape-like hominids that preceded the genus Homo to which we belong, and has found that they used up less energy on a gentle stroll than we do.
Australopithecines had short legs and a wide pelvis. They are typified by "Lucy", a 3.18 million-year-old partial skeleton of Australopithecus afarensis. Modern humans, on the other hand, have longer legs and a narrow pelvis.
Some anthropologists have argued that Lucy's short legs must have made it relatively inefficient for her to get around on the ground. But anthropologist Patricia Kramer of the University of Washington in Seattle, who also trained in engineering, had a hunch this was not necessarily so. Although Lucy would need to take more steps to keep up a certain speed, Kramer reasoned that her shorter legs would take less energy to move. On balance, this might make Lucy the more efficient walker.
To test this idea, Kramer turned to a mechanical model devised by Giovianni Cavagna of the University of Milan. This allowed her to determine the mechanical power requirements of human skeletons and Lucy.
Kramer assumed that the basic lower limb movements of both humans and australopithecines are alike. All modern humans fundamentally walk in the same way, and Lucy's joints suggest that she would have done the same, Kramer says.
She found that although Lucy would have taken more steps to cover a given distance, she would indeed use up less energy during the stroll (The Journal of Experimental Biology, vol 202, p 2807). "The energetic advantages are very real," Kramer concludes. "This analysis clearly indicates that Lucy was not fundamentally compromised by her short legs."
Lucy's skeleton prevented her from walking as fast as we can. "There is a cost," says Kramer. But in Lucy's day the environment was more lush and nutrient-rich than now. Only later, around 2.7 million years ago when the climate dried, would hominids have benefited from longer legs that allowed them to travel faster and eventually, to develop a hunter-gatherer lifestyle. Australopithecines had skeletons appropriate for their time, and were not burdened by their anatomy, says Kramer.
Russell Savage of the University of Liverpool, who has modelled Lucy's motion on computers, says the work is valuable. "It strengthens the argument that Lucy was an efficient biped," he says.
Author: Matt Walker
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