Modern DNA studies, coupled with decades of field work by anthropologists, have given us a fairly good understanding of early human migration. Man evolved in East Africa about 125,000 years ago, as the third glacial period of the Pleistocene (the Illinoian Glaciation) was drawing to a close. Over the next 50,000 years, humans spread throughout sub-Saharan Africa; their northward migration was likely impaired by expansion of the North African desert during this warm, interglacial period.
By the onset of the Wisconsin Glaciation, about 75,000 years ago, man had spread to the southern coast of Asia and, by 60,000 years ago, had reached southeast Asia and Australia. Lowering sea levels produced land bridges throughout the Indonesian archipelago but humans managed to cross a wide swath of the ocean to reach Australia. Japan was colonized by 50,000 years ago, presumably via a land bridge from the east coast of Asia. As the cooler, wetter climate caused the Middle Eastern deserts to retract, man spread northward into Europe and western Asia about 40,000 years ago; there he encountered Neandertals who had inhabited Eurasia for over 150,000 years (and who would disappear within 10,000 years of man's arrival).
Humans reached Siberia 30,000 years ago and crossed to North America via the Bering land bridge. Within another 10,000 years they managed to spread throughout the Americas; some populations likely moved down the Pacific Coast while others crossed through an interglacial corridor, east of the Rockies. Recent evidence suggests that a third population may have reached North America from Europe, hunting and camping along the North Atlantic Ice Shelf. Cuba and other Caribbean islands were colonized about 7000 years ago.
Polynesians set out to explore the Pacific at least 6000 years ago and colonized Samoa about 3000 years ago. Their continued explorations led them to the Marquesas Islands in 300 AD, Easter Island in 318 AD, Hawaii in 500 AD and both Tahiti and New Zealand about 800 AD. By then, only Antarctica remained untouched by humans.
