The problem here is that ancient DNA does not look to agree with you. I've mentioned a few times the Ust-Ishim case
http://dienekes.blogspot.fi/2014/10/...5000-year.html
I repeat, Ust-Ishim was equidistant to WHG types and modern East Asians. Ust-Ishim belonged to Y-dna K, which is the Big Daddy of the majority of modern Eurasian daddy-lineages (R,Q,O,N, etc). There was also the case of the 40K old Tianyuan Man from China who was equidistant to wide range of Eurasian populations (North Euros, Amerinds, East Asians)
To me all of this seems to suggest that the split between Eurasians happened somewhere in Northern Eurasia. Which makes your scenario, that Mal'ta boy was some kind recent immigrant, from Mideast?, Europe? or whatever, long after the East Eurasians had made their long trek east, a somewhat doubtful case.
Here is the rather well known picture from Lazaridis
If you follow that tree, you see that the first split happened between WHG/ANE/ENA clade and BE, then the second between WHG/ANE and ENA, and the final between WHG and ANE. Now there are some people who like to claim that it is perfectly valid and logical to call both BE and WHG/ANE West Eurasian. I disagree, I see a logical block there. So instead of the rigid traditional dichotomy of West and East, I would rather see Eurasia, as a at least three part phenomena (I think the French have a word for this?): one block of Europe/North Eurasia, one bock of East Eurasia and one block of West Eurasia.
This in the case Lazaridis tree is correct. However I strongly suspect the concept of Basal Eurasian just represents African admix radiating from the MENA block. So it could in fundamental sense just be a WHG type guy with ancient post-OOA African admix. Indeed Sardinians who are a good EEF proxy, have the highest African affinity in Europe. In that case the traditional East Eurasia/West Eurasia split is of course valid.
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