How did humans evolve?

Human evolution was not a straight line from ape to human but a branching tree with many dead ends. The human lineage diverged from our closest living relatives, chimpanzees, roughly 6-7 million years ago in Africa. Since then, dozens of hominin species have existed — most of them now extinct.

The first major adaptation was bipedalism — walking upright on two legs — which evolved around 6-7 million years ago. This freed the hands for carrying and tool use. The earliest known stone tools appear around 3.3 million years ago, though they may have been made by species other than our own genus Homo.

Homo habilis, one of the first members of our genus, appeared around 2.8 million years ago with a notably larger brain than earlier hominins. Homo erectus followed around 2 million years ago — the first hominin to control fire, the first to leave Africa, and the first with a body plan similar to modern humans.

Brain size continued to increase over the next million years, driven by factors including tool use, social complexity, language development, and dietary changes (particularly the adoption of cooking, which made more calories available for brain growth). Homo sapiens appeared in Africa around 300,000 years ago, but it took another 230,000 years before the "Cognitive Revolution" around 70,000 years ago produced the full suite of modern human behavior: complex language, abstract thought, art, and the cultural flexibility that allowed our species to colonize the entire planet.