The world's first and longest migration
Modern humans (Homo sapiens) emerged in Africa 300,000 years ago but remained confined to Africa until roughly 70,000-60,000 years ago. Then, in a series of waves over millennia, small groups crossed into the Middle East, followed Australia (by 45,000 years ago), reached Europe (by 40,000 years ago), and eventually occupied every continent. This out-of-Africa migration took 60,000+ years, making it vastly slower than modern migrations but ultimately more complete.
This expansion was enabled by cognitive and behavioral modernity: language, tool sophistication, clothing, and ability to collaborate in large groups. Genetic evidence shows all non-African humans descend from a founding population of perhaps 5,000-20,000 individuals who left Africa and populated the globe.
Adaptation and divergence across climates
As humans spread, they adapted to vastly different environments. Populations in far northern regions developed lighter skin to maximize vitamin D synthesis in low sunlight; equatorial populations retained dark skin for UV protection. Different groups developed lactose tolerance (in populations with dairy) or altitude adaptations (in Andean and Himalayan populations). These adaptations emerged over 5,000-10,000 years, a blink in evolutionary time.
Despite genetic adaptations, cultural diversity exploded. By the time of European contact with the Americas 500 years ago, humans had developed thousands of languages, subsistence strategies, political systems, and belief systems suited to their environments. This cultural diversity is the most consequential divergence, not the minor genetic variations that appeared subsequently.