[blam]

Take this trip, Journey Of Mankind, that was derived from the DNA studies of Professor Stepen Oppenheimer. Notice he has a human entry to North America around the 25,000 year ago time frame. Also, notice that they became isolated in North America (Meadowcroft) during the Last Glacial Maximum (18-23,000 YA).
It is my opinion that these people are the probable source of the halogroup-X in the Americas and the Obijawa(sp) Indians in that region have the highest percentage of the halo-X of all others in the Americas.

I don't rule out the possibility that some Halo-X may also have arrived from across the Atlantic.

[Varda]

", Journey Of Mankind,"

That's pretty close to the scenario Spencer Wells paints in "The Journey of Man" and Cavalli-Sforza has in "The Great Human Diasporas". While I think Europe as a possible source of NAs is unlikely the article linked above suggests the two populations are related being members of subgroup X2.

" Finally, phylogeography of the subclades of haplogroup X suggests that the Near East is the likely geographical source for the spread of subhaplogroup X2, and the associated population dispersal occurred around, or after, the LGM when the climate ameliorated. The presence of a daughter clade in northern Native Americans testifies to the range of this population expansion."