In the entire animal kingdom, the human skeleton is practically unique, due to its adaptation to a lifetime of bipedal walking. Our primate ancestors gave up their tree-bound lifestyle for a life of running and hunting game on the plains of Africa, and this led to some changes in the human form. This includes a skeleton featuring long leg bones, arched feet, an upright pelvis, and most of all, an S-shaped spine. All of that gave early humanity many evolutionary advantages, though this comes at a cost, even today. Walking upright means fighting gravity more acutely than other animal species …