It seems that humankind's ancestors took coming down from the trees in their stride. Computer modelling has suggested that the earliest known hominid, Australopithecus afarensis , was as efficient moving around on two legs as modern humans.
This finding implies that the short-legged, stocky creatures that lived between 5.5 million and 1 million years ago did not shuffle around with an ape-like gait but would have strolled about in a similar fashion to people today.
It also suggests that australopithecines may have been able to make foraging expeditions from a home base rather than simply roaming around in groups like chimpanzees.
The modelling done by Bill Sellers, lecturer in human biology at Loughborough University, was the first in which the muscle energy expenditure was taken into account. Previous attempts had calculated efficiency based on a simple mechanical model of a hominid.
Dr Sellers similarly used a standard computer-simulation package to model the biomechanics of australopithecus based on the latest understanding of its body proportions.
But then he added a good model of muscle function so that the real metabolic-energy costs of walking could be calculated. This was subjected to genetic algorithms that found the optimum way to drive the muscles and hence simulate movement.
The results showed the australopithecines were probably very adept at walking. "It would have been as efficient as a modern human," Dr Sellers said.
The calculations, if scaled up to the size of a human, indicated that australopithecines would have been able to walk the same distances as a modern human for the same amount of food energy.
The results will be presented tomorrow to the British Association of Biological Anthropology and Osteoarchaeology's annual conference at the University of Sheffield.