Out of Africa Migration

Homo sapiens left Africa in at least two waves. The first, around 120,000 years ago, reached the Levant but died out. The second, roughly 70,000 years ago, populated every continent — and genetic evidence suggests the entire non-African world descends from as few as 1,000 to 10,000 individuals.

This bottleneck explains why Africans hold more genetic diversity than all other populations combined. As humans spread, local adaptation continued: Tibetans gained oxygen-efficient blood, Arctic peoples developed compact bodies to conserve heat, and equatorial peoples kept tall, lean builds to shed it.