There have been some disparate rightists who have claimed that Kennewick Man (a human who lived in what is now Washington State, USA 8,358 ± 21 14C years before present) is European in ethnic origin. These people are obviously not informed of the genetic study done on The ancestry and affiliations of Kennewick Man which revealed him to be most closely related to modern Native Americans.
The genetic admixture which most closely relates Kennewick Man, Native Americans, and other East Eurasians with Europeans comes from the Ancient North Eurasians (ANE), a population living in Siberia at least 24,000 years ago which was most closely related to early West Eurasians (link, link). Ancient Y chromosomes of this ANE group, uncovered from Mal’ta (MA-1) and Afontova Gora (AG3), belong to the Y chromosomal haplogroup R, a branch of the Y chromosomal haplogroup P which diversified c. 31,900 years before present. Some migrations out of Siberia after this time are likely responsible for the current predominance of Y chromosomal haplogroups Q and R (branches of P) in Native Americans and Northern Europeans, respectively (I happen to belong to R-L513), as well as the ANE admixture found in these groups.
Davidski at Eurogenes also suggests (link) that there may have been a very early incursion of ANEs into the East Eurasian gene pool. If this is true, it may be responsible for the predominance of certain non-P lineages of Y-haplogroup K2, including K2a, K2b1, K2c, K2d, M, N, O, and S (which diverged from the ancestor of haplogroup P around 45400 years before present) among a variety of East Eurasians including the Ust’-Ishim Man from Siberia 45,000 years ago. Keeping in mind that the ANEs were most closely related to early West Eurasians, it is also possible that such an early incursion of ANE admixture is responsible for the East Eurasian presence of Y haplogroup C, which diversified ~47,900 YBP and was also found in some ancient West Eurasians such as Kostenki-14 and the Mesolithic La Brana specimen. Regarding the impact on mitochondrial (maternal) lineages, an early addition and ANE admixture to the East Asian gene pool may have brought mitochondrial haplogroup N which is normally found in West Eurasians, but is also significantly present in some very disparate East Eurasian populations such as Australian Aborigines, and certain Siberian and Native American peoples (and even the Ust’-Ishim specimen).
East Asians such as the Han, Koreans and Japanese also appear to have received a later addition of ANE admixture, but it was much less than that received around the same time by Siberians and the Siberian ancestors of Native Americans (see the supplementary data on pages 145-147 in here). Kennewick Man appears to have received 40-45 % of his genome from this later ANE admixture event; the Han, Koreans and Japanese received about 10-12 %, and the Andamanese Onge, an isolated population in the Indian Ocean, presumably received little to none and was used as a control in the analysis.
What East Eurasians (including Australoid peoples, East Asians, Native Americans, and Siberians) possess which differentiates them from West Eurasians (“Causaoids”) is admixture from another, apparently basal East Eurasian group which diverged 60,000-65,000 YBP from other Eurasians. This basal East Eurasian group seems a likely origin of the East Eurasian presence of Y haplogroup D (which is basal to all other Eurasian Y haplogroups except for E) and mitochondrial haplogroup M, which both formed between 60,000 and 65,000 YBP. Perhaps not coincidentally, both mitochondrial haplogroup M and Y chromosomal haplogroup D reach relative maxima in Tibet and Japan. Somewhat surprisingly, however, Y haplogroup D also diversified around the same time as Y haplogroups C and K2 (~45,000 YBP). This would seem to indicate that the East Eurasian gene pool underwent a population bottleneck until around 45,000 YBP when it received a large amount of ANE admixture (which appears already present in the Ust’-Ishim man from this time period). Under this model, over the next ~40,000 years, the East Eurasian gene pool underwent a massive geographic and genetic diversification.