It's our ability to run, not walk, that sets humans apart as the world's dominant species, researchers say.

According to an anatomical analysis by two U.S. scientists, we're built to run.

Human tendons and ligaments act like springs, features in the skull prevent us from overheating and we have bigger buttocks than most apes for stability while running long distances, the researchers argue.

(Courtesy Nature)

Anthropologists theorize running was a byproduct of bipedalism, the ability to walk on two legs, which they say evolved at least 4.5 million years ago.

University of Utah biology Prof. Dennis Bramble and anthropology Prof. Daniel Lieberman of Harvard University, however, say our early ancestors evolved to be endurance runners 2.5 million years ago.

Before the invention of the bow and arrow, humans had to hunt and compete with vultures and hyena for dying prey on the Africa savannah, the pair said.

In Thursday's issue of the journal Nature, Bramble and Lieberman list more than 24 traits showing how the human body is suited to long-distance running. Had evolution not selected for running then we would look more like apes, they said.

Sprinters versus long-distance runners

Our long legs take lengthy strides while the foot arch acts like a spring and the bigger discs absorb shocks, according to the researchers.

Although humans use more energy to run for our body mass compared to other species, we also have a well-developed system to get rid of excess heat. For example, blood vessels that lie close to the skin's surface on the face and neck help us to perspire.

The running-type features came at a price, though.

"We are very confident that strong selection for running – which came at the expense of the historical ability to live in trees – was instrumental in the origin of the modern human body form," Bramble said in a statement.

Other anthropologists say the first humans likely were able to sprint away from predators, rather than hunt prey over long distances.