Early human beings might have been walking upright 3.5 million years ago, but even the most athletic individuals would have struggled to keep up with a modern couch potato in a running race, research has suggested.

Ancient human relatives such as the famous fossil Lucy, a member of the species Australopithecus afarensis, would have found running almost impossible because they probably lacked Achilles tendons, scientists said yesterday. With the exception of gibbons, all humanity’s closest animal relatives – the chimpanzees, gorillas and orangutans – have no Achilles tendons, and it is highly likely that early hominins such as Lucy did not have them either.

A new computer gait simulation of both Homo sapiens and A. afarensis has revealed that Achilles tendons are critical to fast running speeds. If Lucy lacked such tendons, she could still have walked almost as fast as modern humans, but her top running speed would have been half as quick.

The findings, which were presented to the BA Festival of Science in York, suggest that the evolution of Achilles tendons was critical to our species’ development, allowing us to become hunters. “It opens all sorts of options,” Bill Sellers, of the University of Manchester, said. “If you’re a runner, all of a sudden the idea of hunting becomes possible. Without Achilles tendons, you are rubbish at running. You can’t go very fast, and you use an awful lot of food to get from A to B. Humans and, strangely, gibbons, have great big fat Achilles tendons.

“Pursuit hunting pretty much relies on running. If Lucy had no Achilles tendon, she’d be far too inefficient to have been any kind of pursuer. It wouldn’t have stopped her from scavenging, but she would not have been much of a hunter.”

Evidence for the evolution of Achilles tendons is sparse because few hominin fossils have intact feet. The shape of other bones suggests that the features did not evolve until perhaps two million years ago, probably in Homo erectus, a species thought to be a direct ancestor of modern humans.

“I would be very surprised if Homo erectus couldn’t run,” Dr Sellers said. “If you look at the skeleton, it looks virtually like a modern human from the neck down, so I would be very surprised if there was no Achilles tendon. Lucy, however, lived 3.5 million years ago, and doesn’t look at all like humans. I think there’s every chance that Lucy couldn’t run.”

The benefit of an Achilles tendon is that it acts like a giant spring, storing energy and producing an efficient running gait. “Efficient running would have been essential to allow our ancestors to move from a largely herbivorous diet to the much more familiar hunting activities associated with later humans,” Dr Sellers said. “What we need to discover now is when in our evolution did we develop an Achilles tendon, as knowing this will help unravel the mystery of our origins.”

Dr Sellers’s computer gait models have been used to show that Lucy almost certainly walked upright, and at a speed only a little slower than that of modern human beings. He recently published similar research revealing that a small dinosaur named Compsognathus may have been the fastest two-legged creature ever to have lived, with a top speed of almost 40mph.

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