Bipedalism
Explore bipedalism — the ability to walk upright on two legs, which freed human hands and set the stage for tool use, brain growth, and civilization.
Bipedalism — habitual upright walking on two legs — is the defining physical characteristic of the hominin lineage. It emerged roughly 6 to 7 million years ago, millions of years before the first stone tools, the expansion of the brain, or the development of language. In many ways, standing up was the first step toward becoming human.
The reasons for the evolution of bipedalism remain debated. Hypotheses include the need to see over tall savanna grass, the energy efficiency of walking on two legs over long distances, the advantage of freeing hands for carrying food or infants, and the reduced heat exposure of an upright body in the tropical sun. The truth likely involves a combination of these factors, varying across different environments and species.
The consequences of bipedalism were profound. Free hands could carry objects, manipulate tools, and eventually create technologies. The restructuring of the pelvis and birth canal that came with upright walking may have contributed to the evolution of smaller-brained, more helpless infants — which in turn demanded more intensive parenting and social cooperation. Bipedalism was not just a mode of locomotion; it was the physiological foundation upon which everything distinctively human was built.