American Indians are the descendants of the inhabitants of North and South America before the coming of Europeans in 1492. Another term, "Native American", is sometimes also used to refer to American Indians in order to distinguish them from the people of India, and to emphasize their American ancestry.
In the United States there are 562 Native American tribes that retain their independent sovereignty.
The widely taught theory that American Indians are descendants of migrants from Asia, who crossed the Bering Straitland bridge during an Ice Age, is almost certainly false according to TIME magazine. Liberal archaeologists long insisted that this took place as early as 10,000 years ago. But the facts are that American Indians have very different characteristics from Asians, ranging from blood types to DNA, most likely due to thousands of years of reproductive isolation as well as adaptations forced by separate climates, nutritional availability, and survival tactics. Recent linguistic study shows no connection between American Indian and East Asian language, and archaeological evidence shows that each population used fundamentally different tools, suggesting no technology transfer via migration..
People today who are only partly descended from those early American Indians are still considered to be American Indians if they maintain tribal affiliation or community attachment. However, each Indian tribe or band has its own definitions regarding membership, some based on historical tradition, others based on rules (like blood quanta) imposed by the US Government.
In 1996 there was a discovery of fragments of a skeleton called the Kennewick Man. But serious doubts about the authenticity of these remains have resulted in litigation and criticism. Some claimed that radiocarbon dating supported an age of more than 9000 years. The morphology of the Kennewick Man remains is said to differ from that of present day Native Americans, suggesting a different ancestry but there remains significant controversy about that.
Despite this controversy, there has been significant evidence that certain Indian tribes do have ties to Asian peoples. For instance, numerous American Indians and Mongolians share a physical trait, known as "shovel tooth" in which the incisor has a distinctive shovel-like shape. According to geneticists, this cannot be a coincidence.  Another interesting piece of evidence has to do with skull measurements. According to skull measurements done in 2001 at the University of Michigan, scientists have suggested that Blackfoot, Sioux, and Cherokee Indians may have descended from the ancient, indigenous Jomon people of Japan, and related to the Ainu ethnic minority on the island of Hokkaido.
Some creation scientists have pointed to the American Indian population's lack of any ties to other populations as evidence of biblical veracity. However, it is also true that American Indian creation myths are remarkably similar to the biblical Genesis account. The population was established after the destruction of the Tower of Babel, as God dispersed the nations, their languages, and skills. 
- TIME - Who Were The First Americans?, By MICHAEL D. LEMONICK, ANDREA DORFMAN, Sunday, Mar. 05, 2006 
- For example, American Indians have among the highest percentage for any ethnicity of blood type "O", while Asians have the lowest percentage. As another example, American Indian fingerprint patterns are strikingly different from Asians'.
- Fortescue, Michael D., Language Relations Across Bering Strait: Reappraising the Archaeological and Linguistic Evidence, 87-108.
- American Indian Creation Myths
- Ronald L. Numbers, The Creationists: From Scientific Creationism to Intelligent Design, 467.