The upper body, meanwhile, carries its own made-for-running designs, including wide shoulders -- good for swinging arms from for balance as we stride -- and lighter forearms that are easy to move back and forth. Even our heads are equipped for running, they say, as a large ligament stretching from our spines to the back of our heads acts to dampen the oscillation of our heads as we plod along.
Finally, our ability to sweat is unmatched with our estimated 3 million sweat glands. Couple that with the fact that we aren't very furry and you have a cool, running machine.
Bernd Heinrich, a world record holder in the ultra marathon and biologist at the University of Vermont in Burlington, says the authors' points make sense.
"Most of us don't do much running so it may not feel natural, but it feels natural to me," he said. "Not much is new here, but I think they bring together a lot of evidence so it all fits into a pattern."
While few anthropologists argue with the fact that humans evolved to become good runners, Lovejoy remains skeptical we were specifically designed for endurance running.
"There is little doubt that many of the bony features that are mentioned … are adaptations to running and walking, but there is no evidence that they are specifically adapted to endurance running," he said.
Lovejoy points out that our arms and legs could also be considered well designed for swimming, but that doesn't necessarily mean we evolved specifically to be elite swimmers.
But Lieberman and others counter that endurance running, unlike swimming, could have been a key part of early man's survival. It may have helped them during long hunts and in scouting out abandoned carcasses first, for example.
"Being fast would have been a huge premium," said Heinrich. "Vultures can come in and devour a dead cow in an hour or two. So ideally, the humans would get there first."
Patricia Kramer of the University of Washington, points out there may be a small glitch in that theory. According to most research, early female humans likely did not participate in long hunts, but stayed behind to care for the young. If this is the case, Kramer asks, why would women also have evolved to be good long-distance runners?
"If endurance running was a male activity, then why do women have small waists and hypotrophied gluteus maximae?" she asks. "I think that understanding how we moved through our environment is critical to understanding who we are as evolved primates … but as with all good research this causes us to ask a new set of questions."