Walking goes way back. The first fish-like creatures to come ashore barely inched along, and used gills to breathe as they slugged through the muck while moving between watering holes.
Among the first creatures to make the move from a sprawled posture to an upright, two-legged stance were the dinosaurs, most notably the therapods, a group of dinosaur that includes Tyrannosaurs Rex and the raptors. Today’s birds are the descendents of therapods, and they too walk on two legs.
When, and why, our early primate ancestors became bipedal is currently a subject of intense debate. According to one popular theory, early hominins clambered down from the trees some 7 million years ago, as Earth was undergoing a period of global cooling and forests in Africa became patchy. Over the next several million years, the idea goes, our ancestors evolved from hunched, knuckle-walking primates to creatures that stood and walked upright.
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But recent studies involving observations of primates in the wild are beginning to challenge this theory. These studies suggest our ancestors might have experimented with bipedalism while still living in the trees and were better prepared than previously thought to walk upright when they descended.
We humans are an exception among mammals and most of the animal kingdom with our upright mode of walking. Other animals and insects still do quite well moving around on four legs or more.
One reason for this is bipedalism is not particularly well suited for moving fast. Many four legged animals run faster than us. Horses are expert runners. Greyhound dogs have mastered the art of cornering. Even elephants, which might appear to just be walking fast, are technically runners.
Whether on two legs or four, walking is proving to be an extremely difficult thing for engineers to recreate in robots. While some robots manage to walk faster than humans, they look stiff doing it. The fact that efforts to create walking robots either fail outright or achieve a very crude kind of success reveals just how complex the act of walking is:
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