Many thousands of years before Christopher Columbus’ ships landed in the Bahamas, a different group of people discovered America: the nomadic ancestors of modern Native Americans who hiked over a “land bridge” from Asia to what is now Alaska more than 12,000 years ago. In fact, by the time European adventurers arrived in the 15th century A.D., scholars estimate that more than 50 million people were already living in the Americas. Of these, some 10 million lived in the area that would become the United States. As time passed, these migrants and their descendants pushed south and east, adapting as they went. In order to keep track of these diverse groups, anthropologists and geographers have divided them into “culture areas,” or rough groupings of contiguous peoples who shared similar habitats and characteristics. Most scholars break North America—excluding present-day Mexico—into 10 separate culture areas: the Arctic, the Subarctic, the Northeast, the Southeast, the Plains, the Southwest, the Great Basin, California, the Northwest Coast and the Plateau.