Washington ? Runners and joggers, take pride: Your favorite exercise may be responsible for the evolution of human beings from our apelike ancestors.

About 2 million years ago, our ancient forefathers developed bones and muscles suited for long-distance running, the better to hunt animals or scavenge for carcasses on the plains of Africa, a team of anthropologists reported Wednesday in the journal Nature.

Over time, they said, these physiological traits separated primitive people from the line that led to chimpanzees, our closest evolutionary relatives, whose bodies remained more fit for climbing trees.

“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,” said Dennis Bramble, a biology professor at the University of Utah in Salt Lake City. “Running made us human, at least in an anatomical sense.”

Bramble and his partner, Daniel Lieberman, a professor of anthropology at Harvard University in Cambridge, Mass., listed 26 physiological traits that make for endurance, if not speed, in runners. Compared with chimps, for example, humans have shorter arms, longer legs, springy calf and foot tendons, shoulders that rotate and bulky buttocks for better balance.

“Your gluteus maximus (main buttocks muscle) stabilizes your trunk as you lean forward in a run,” Lieberman said. “A run is like a controlled fall, and the buttocks help to control it.”

Another feature early humans developed is a piece of tissue at the back of the skull and neck that acts as a shock absorber and helps the arms and shoulders counterbalance the head as it bobs during a run.

“These esoteric features make humans surprisingly good runners,” Lieberman said. “Over long distances, we can outrun our dogs and give many horses a good race.”

While people cannot run as fast, over short distances, as horses, greyhounds or antelopes, they can keep running for many miles.

Kansas University track great Wes Santee is shown in this 1954 photo. Santee died Sunday at the age of 78.

“Apes, such as chimpanzees, can sprint rapidly, but they do so rarely and only for short distances,” the researchers wrote. “No primates other than humans are capable of endurance running.”

Our ancestors learned to walk long before they began to run. Anthropologists think our ancient predecessors, known as Australopithecines (“southern apes”) were able to walk well on two legs at least 4.4 million years ago.

The physical changes that made endurance running possible do not appear in the fossil record until an early species of the human family, known as Homo erectus, arrived about 2 million years ago.

“Long legs relative to body mass first appear unequivocally 1.8 million years ago with Homo erectus,” the Nature researchers wrote.