The researchers do not know why natural selection favored human ancestors who could run long distances. For one possibility, they cite previous research by University of Utah biologist David Carrier, who hypothesized that endurance running evolved in human ancestors so they could pursue predators long before the development of bows, arrows, nets and spear-throwers reduced the need to run long distances.
Another possibility is that early humans and their immediate ancestors ran to scavenge carcasses of dead animals – maybe so they could beat hyenas or other scavengers to dinner, or maybe to "get to the leftovers soon enough," Bramble says.
Scavenging "is a more reliable source of food" than hunting, he adds. "If you are out in the African savannah and see a column of vultures on the horizon, the chance of there being a fresh carcass underneath the vultures is about 100 percent. If you are going to hunt down something in the heat, that's a lot more work and the payoffs are less reliable" because the animal you are hunting often is "faster than you are."