Marathon enthusiasts wouldn’t be able to run their races if humans had evolved differently, and beauty queens would be judged by much different standards.
A new study by U professor of biology Dennis Bramble and Harvard anthropologist Daniel Lieberman have shown that humans had to evolve in order to run long distances.
“Without this evolution, we may have called ourselves human and maybe thought the way we think, but we would not look the way we do,” Bramble said.
But it wasn’t looks that human ancestors were going for; they were trying to survive.
While early members of the genus Homo could run, Bramble doesn’t believe it was to run down prey, but rather to either run to a recently killed carcass or chase animals to the point of exhaustion, which is called pursuit predation.
“Chasing down animals that are way faster than you just isn’t very probable,” Bramble said.
However, pursuit predation was more likely, as the technique was used by hunter-gatherers in the past, and after Bramble’s article ran in the journal Nature, he said he received eyewitness accounts of this type of predation still taking place in parts of Africa.
The other hypothesis of for why ancestral humans may have run long distances also makes sense to Bramble.
“It was important to have fresh meat, but it was likely killed by someone or something else-normal predators. If clued in by a column of vultures, the hominid could have run that distance and gotten to the carcass while there was still something left,” Bramble said.
Humans’ ape-like ancestor, Australopithecus afarensis, didn’t have the ability to run due to the fact that it had long arms, high shoulders and short legs. The species inhabited the Earth about 4.5 million years ago. The species walked bipedally when it was on the ground, but spent much of its time climbing trees, Bramble said.
About 2.5 million years later, Homo erectus came onto the scene with shorter arms, longer legs and dropped shoulders, among other changes. As the Homo genus developed, so did its skeletal structure to make it not a better walker, but a better runner, Bramble said.
Bramble cites various findings in the fossil record that prove that humans ran. Some of these include well-developed “leg springs,” such as the Achilles tendon and the foot arch.
“These features aren’t active when you’re walking, but as soon as you start running even at a slow jog, they help absorb shock and make running more efficient,” he said.
Another big development was in dropping the shoulders from up around the ears. Being able to rotate the torso independently of the head and neck is necessary to counterbalance the legs during running, Bramble said.
The physical changes that occurred between Australopithecus and Homo were significant because they allowed humans to move away from life in the trees to life on the ground.
Bramble says that, according to the fossil record, the change from living mainly in trees to the ground was only the beginning of a chain of evolution.
“The development of running is a major change in lifestyle-breaking away from trees and running around-and running created a redeveloped body. The behavioral changes associated with running may ultimately have promoted the increase in cranial capacity as well.”
Bramble first became interested in the research when he read earlier research by U biologist David Carrier, who was looking at running in connection with things like hairlessness and sweat glands, which can’t be traced in the fossil record.
However, Bramble and Lieberman plan future research on how humans stabilize their heads while running, and also to go back through the fossil record to see if he can find more information about Homo habilis, the first well-known species of the Homo genus.
“We want to see if we can get a better sense of when these [running] features begin to appear,” he said.