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
鈥淟ucy鈥�, 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鈥檚 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.
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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鈥檚 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). 鈥淭he energetic advantages are
very real,鈥� Kramer concludes. 鈥淭his analysis clearly indicates that Lucy was not
fundamentally compromised by her short legs.鈥�
Lucy鈥檚 skeleton prevented her from walking as fast as we can. 鈥淭here is a
cost,鈥� says Kramer. But in Lucy鈥檚 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鈥檚 motion
on computers, says the work is valuable. 鈥淚t strengthens the argument that Lucy
was an efficient biped,鈥� he says.