The human skeleton is the product of millions of years of evolution, and human beings can do something even our closest primate ancestors cannot: walk upright for a lifetime. Our early ancestors gave up their vegetarian, tree-bound lifestyle to start running and hunting game as the rainforests of Africa shrank, and the human form adapted. By now, the human skeleton features an S-shaped spine, an upright pelvis, long leg bones, and arched feet, all geared for a lifetime of walking and running upright. This gave our ancestors many advantages, but this body form does takes its toll. An upright body …