Like Homo erectus had earlier, groups of Homo sapiens moved. By 200,000 years ago they had begun to spread across Africa, and by 120,000 years ago they had begun to migrate out of Africa to Eurasia (see Map 1.1). They most likely walked along the coasts of India and Southeast Asia, and then migrated inland. At the same time, further small evolutionary changes led to our own subspecies of anatomically modern humans, Homo sapiens sapiens (which literally translates as “thinking thinking humans”). Homo sapiens sapiens moved into areas where there were already Homo erectus populations, eventually replacing them, leaving Homo sapiens as the only survivors and the ancestors of all modern humans.

The best-known example of interaction between Homo erectus and Homo sapiens sapiens is that between Neanderthals (named after the Neander Valley in Germany, where their remains were first discovered) and a group of anatomically modern humans called Cro-Magnons. Neanderthals lived throughout Europe and western Asia beginning about 150,000 years ago, had brains as large as those of modern humans, and used tools, including spears and scrapers for animal skins, that enabled them to survive in the cold climate of Ice Age central Europe and Russia. They built freestanding houses and decorated objects and themselves with red ochre, a form of colored clay. They sometimes buried their dead carefully with tools, animal bones, and perhaps flowers, which suggests that they understood death to have a symbolic meaning.

Cro-Magnon peoples moved into parts of western Asia where Neanderthals lived by about 70,000 years ago, and into Europe by about 45,000 years ago. The two peoples appear to have lived side by side for millennia, hunting the same types of animals and gathering the same types of plants. The last evidence of Neanderthals as a separate species comes from about 30,000 years ago, and it is not clear exactly how they died out. They may have been killed by Cro-Magnon peoples, or they simply may have lost the competition for food as the climate worsened around 30,000 years ago and the glaciers expanded.

Homo erectus migrated great distances, but Homo sapiens sapiens made use of greater intelligence and better toolmaking capabilities to migrate still farther. They used simple rafts to reach Australia by at least 50,000 years ago, and by 35,000 years ago had reached New Guinea. By at least 15,000 years ago, humans had walked across the land bridges then linking Siberia and North America at the Bering Strait and had crossed into the Americas. Because by 14,000 years ago humans were already in southern South America, ten thousand miles from the land bridges, many scholars now think that people came to the Americas much earlier. They think humans came from Asia to the Americas perhaps as early as 20,000 or even 30,000 years ago, walking or using rafts along the coasts. (See Chapter 11 for a longer discussion of this issue.)

With the melting of glaciers sea levels rose, and parts of the world that had been linked by land bridges, including North America and Asia as well as many parts of Southeast Asia, became separated by water. This cut off migratory paths but also spurred innovation. Humans designed and built ever more sophisticated boats and learned how to navigate by studying wind and current patterns, bird flights, and the position of the stars. They sailed to increasingly remote islands, including those in the Pacific, the last parts of the globe to be settled. The western Pacific islands were inhabited by about 2000 B.C.E., Hawaii by about 500 C.E., and New Zealand by about 1000 C.E. (For more on the settlement of the Pacific islands, see “Settlement of the Pacific Islands” in Chapter 12.)

Once humans had spread out over much of the globe, groups often became isolated from one another, and people mated only with other members of their own group or those who lived nearby, a practice anthropologists call endogamy. Thus, over thousands of generations, although humans remained one species, Homo sapiens sapiens came to develop differences in physical features, including skin and hair color, eye and body shape, and amount of body hair. Language also changed over generations, so that thousands of different languages were eventually spoken. Groups created widely varying cultures and passed them on to their children, further increasing diversity among humans.