http://www.runtheplanet.com/resources/historical/
It goes right back to the beginning:
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—and the ability to run shaped our anatomy, making us look like we do today. That is the conclusion of a study by University of Utah biologist Dennis Bramble and Harvard University anthropologist Daniel Lieberman. Bramble and Lieberman argue that our genus, Homo, evolved from more ape-like human ancestors, Australopithecus, two million or more years ago because natural selection favored the survival of australopithecines that could run and, over time, favored the perpetuation of human anatomical features that made long-distance running possible.
"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".
Anatomical features that help humans run
Here are anatomical characteristics that are unique to humans and that play a role in helping people run, according to the study:
Skull features that help prevent overheating during running. As sweat evaporates from the scalp, forehead and face, the evaporation cools blood draining from the head. Veins carrying that cooled blood pass near the carotid arteries, thus helping cool blood flowing through the carotids to the brain.
A more balanced head with a flatter face, smaller teeth and short snout, compared with australopithecines. That "shifts the center of mass back so it is easier to balance your head when you are bobbing up and down running", Bramble says.
A ligament that runs from the back of the skull and neck down to the thoracic vertebrae, and acts as a shock absorber and helps the arms and shoulders counterbalance the head during running.
Unlike apes and australopithecines, the shoulders in early humans were "decoupled" from the head and neck, allowing the body to rotate while the head aims forward during running.
The tall human body—with a narrow trunk, waist and pelvis—creates more skin surface for our size, permitting greater cooling during running. It also lets the upper and lower body move independently, "which allows you to use your upper body to counteract the twisting forces from your swinging legs", Bramble says.
Shorter forearms in humans make it easier for the upper body to counterbalance the lower body during running. They also reduce the amount of muscle power needed to keep the arms flexed when running.
Human vertebrae and disks are larger in diameter relative to body mass than are those in apes or australopithecines. "This is related to shock absorption", says Bramble. "It allows the back to take bigger loads when human runners hit the ground".
The connection between the pelvis and spine is stronger and larger relative to body size in humans than in their ancestors, providing more stability and shock absorption during running.
Human buttocks "are huge", says Bramble. "Have you ever looked at an ape? They have no buns". He says human buttocks "are muscles critical for stabilization in running" because they connect the femur—the large bone in each upper leg—to the trunk. Because people lean forward at the hip during running, the buttocks "keep you from pitching over on your nose each time a foot hits the ground".
Long legs, which chimps and australopithecines lack, let humans to take huge strides when running, Bramble says. So do ligaments and tendons—including the long Achilles tendon—which act like springs that store and release mechanical energy during running. The tendons and ligaments also mean human lower legs that are less muscular and lighter, requiring less energy to move them during running.
Larger surface areas in the hip, knee and ankle joints, for improved shock absorption during running by spreading out the forces.
The arrangement of bones in the human foot creates a stable or stiff arch that makes the whole foot more rigid, so the human runner can push off the ground more efficiently and utilize ligaments on the bottom of the feet as springs.
Humans also evolved with an enlarged heel bone for better shock absorption, as well as shorter toes and a big toe that is fully drawn in toward the other toes for better pushing off during running.
The study by Bramble and Lieberman concludes: "Today, endurance running is primarily a form of exercise and recreation, but its roots may be as ancient as the origin of the human genus, and its demands a major contributing factor to the human body form".
^Fantastic breakdown, this is a section from a really good section of the website listed at the top, this specific section is from http://www.runtheplanet.com/resources/historical/runevolve.asp
posted by Izzy
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