Here's a Principal Component Analysis (PCA) and an accompanying biplot based on output from an improved version of my ANE K7 ancestry test. Let's call it the West Eurasia K8. This one gives more accurate estimates of Western European Hunter-Gatherer (WHG) and Near Eastern admixture proportions, thanks to the use of new ancient samples.
here), the results are basically indistinguishable from those I get with genotype data (for instance, see here and here), which suggests that they're correct and based on ancestry proportions that are close to the truth. The Past3 data sheet used to create the PCA is available here. You can view a spreadsheet of the results with extra samples here.
Clearly, ANE is the main agent causing the west to east differentiation in dimension 2. Note that even a small rise in ANE, say, 4-5%, creates significant distance between samples on the PCA plot.
East and South Eurasian admixture has a similar effect, but must be more considerable to make an impact on a West Eurasian-specific PCA like this (and it does with the obvious Volga-Ural outliers, who come from Chuvashia and Tatarstan).
On the other hand, Near Eastern admixture without ANE creates almost the opposite effect. Note, for instance, that Neolithic genomes Stuttgart and NE1 show much higher levels of Near Eastern ancestry than most Europeans, and yet they're amongst the most western samples on the plot.
This suggests that the Near East, and in particular the Caucasus, experienced a significant rush of ANE admixture after early Neolithic farmers left the region for Europe. Alternatively, Caucasus populations may have carried even higher levels of ANE than they do today, before newcomers from the Near East mixed with them. But either way, a lot of ANE arrived in the Near East at some point.
It also suggests that, overall, the populations that moved west across northern Europe after the Neolithic, and shifted northern European genetic structure to the east, did not carry high ratios of Near Eastern ancestry. Instead, they harbored high ratios of ANE and WHG. What these ratios were exactly I haven't a clue, but ancient DNA should tell us that soon.
Below are the ancestry proportions for the five ancient genomes in this analysis, in chronological order. It's interesting to note (yet again) the rising and falling Near Eastern admixture, from the Mesolithic to Neolithic and then from the Neolithic to Bronze Age, respectively, as well as the steady rise of ANE from the Bronze Age to the Iron Age.
BR2 (Bronze Age)
Hinxton4 (Iron Age)
The fateful triangle
Bell Beaker, Corded Ware, EHG and Yamnaya genomes in the fateful triangle