Walking Is Central to Human Evolution, but Nobody Knows Why
One of the oddest, most improbable things about humans is that we are habitual bipeds. That is, we walk most of the time on two legs.
Lots of mammals can and do walk on two legs: bears, lemurs, capuchin monkeys. But humans are the only mammals who do it habitually — all the time, everywhere we go. Once you learn about the complexity and difficulty of bipedal walking you start to realize how truly out of the ordinary this habit is.
For every step you take, your brain has to make an estimated billion calculations. The vestibular system in your inner ear feeds your brain information about distance, balance, orientation within the environment you’re traversing, and — the detail that always blows my mind — the gravitational pull of the planet. No matter where you’re heading, you’re doing it on a ball in space spinning at about 1,000 miles per hour. Your brain has to account for that motion.
At the same time, your proprioception feeds back other information about the territory underfoot — icy, rocky, flat, bumpy — allowing you to respond automatically to changing terrain. There are infinite variations on the kinds of encounters your body has with the world, and your brain has to accommodate all of them to keep you upright.
