Human running and evolution
THE ABILITY to run shaped our anatomy, making us look like we do today. Humans evolved from ape-like ancestors because they needed to run long distances perhaps to hunt animals or scavenge carcasses on Africa's vast savannah.
That is the conclusion of a study published in the journal Nature by University of Utah biologist Dennis Bramble and Harvard University anthropologist Daniel Lieberman.
Because natural selection favoured the survival of australopithecines that could run and, over time, favoured the perpetuation of human anatomical features that made long-distance running possible, Bramble and Lieberman argue that our genus, Homo, evolved from more ape-like human ancestors, Australopithecus, 2 million or more years ago.
``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," says Bramble, a professor of biology. "Running has substantially shaped human evolution. Running made us human at least in an anatomical sense. We think running is one of the most transforming events in human history. We are arguing the emergence of humans is tied to the evolution of running."
That conclusion is contrary to the conventional theory that running simply was a byproduct of the human ability to walk. Bipedalism the ability to walk upright on two legs evolved in the ape-like Australopithecus at least 4.5 million years ago while they also retained the ability to travel through the trees. Yet Homo with its "radically transformed body" did not evolve for another 3 million or more years Homo habilis, Homo erectus and, finally, our species, Homo sapiens so the ability to walk cannot explain anatomy of the modern human body, Bramble says.
Running, not walking
"There were 2.5 million to 3 million years of bipedal walking [by australopithecines] without ever looking like a human, so is walking going to be what suddenly transforms the hominid body?" he asks. "We're saying, no, walking won't do that, but running will."
Walking cannot explain most of the changes in body form that distinguish Homo from Australopithecus, which when compared with Homo had short legs, long forearms, high permanently "shrugged" shoulders, ankles that were not visibly apparent and more muscles connecting the shoulders to the head and neck, Bramble says.
If natural selection had not favoured running, "we would still look a lot like apes," he adds. Bramble and Lieberman examined 26 traits of the human body that enhanced the ability to run. Many were also seen in fossils of Homo erectus and some in Homo habilis.
Only some of them were needed for walking. Traits that aided running include leg and foot tendons and ligaments that act like springs, foot and toe structure that allows efficient use of the feet to push off, shoulders that rotate independently of the head and neck to allow better balance, and skeletal and muscle features that make the human body stronger, more stable and able to run more efficiently without overheating.
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