According to archaeological and genetic evidence, the first Americans came from northeast Asia. Up to 28,000 years ago, a small distinct population of humans crossed the Bering Strait land bridge to populate the northwestern section of North America. The population eventually moved south and east from there.
Geneticists have identified a small group of approximately 1,000 people who split off from other Asian groups between 30,000 and 23,000 years ago. These people, according to a mix of archaeological and biological evidence, were the ancestors of today's Native Americans.
While the Asian answer appears to be correct for now, it does not account for several anomalies uncovered by archaeologists. For example, Kennewick Man and other skulls discovered in North America and dating back 10,000 years or more have distinctly European features, appearing very different from early Native American remains. One controversial hypothesis is that Solutreans, an upper Paleolithic culture from Europe, may have traveled across northern pack ice or even sailed from Europe to the eastern coast of North America at about the same time Asians traveled to the western coast. A more accepted hypothesis is that the changes in Kennewick Man and others are forms of environmental evolution caused primarily by the transition from hunting to farming lifestyles.