In the quiet repetition of every human step, a story of survival is encoded. Penn State researchers have found that the heel-first gait unique to humans — far more consistent than the variable foot-landings of chimpanzees — saves between 26 and 41 percent of the metabolic energy required to walk otherwise, a difference that, compounded across lifetimes and landscapes, may have allowed early humans to range farther, hunt longer, and ultimately inhabit the world. The body adapted to bear the cost: thicker heel bones, stronger joints, a skeleton quietly reengineered for endurance. Now, as we walk