The science of man, including the study of the distribution of physical and cultural attributes in relation to man's origin, location, history, and environment; -- sometimes used in a limited sense to mean the study of man as an object of natural history, or as an animal. {1913 Webster}
Well, there is one thing certain about anthropology: it is not much of a science. No two anthropologists agree exactly on very much and all have their prejudices mixed, to varying degrees, in their conclusions.
I have read several books, including compilations, about the origin of North American natives. My best guess is that eastern US tribes like the Delaware, Mohawk and Cherokee (of which I am 1/16) are all Caucasian and have European roots, although ancient.
The Eskimo are people who were kicked out of the islands now known as Japan, and are relatively recent. The far-north tribes in Alaska and Canada came over the top of the planet from Siberia and are similar to many people from the Holarctic region.
South of the US are people who are Proto-Australian, a group whose ancestors are extinct .They once ruled some of the Pacific islands and Australia, but were driven out by aggressive immigration by newer tribes from Africa and Asia Minor.