The above diagram is from the Lazarides paper from December of 2013.
You may know that the Eurogenes blog (along with some very prominent researchers) has been heavily and stubbornly promoting the theory of a very sudden invasion of Europe during the Copper Age from either the Ponto-Caspian Steppe or the Central Asian Steppe.
If you look in the comments of this post (January 14, 2015 at 10:46 PM), you'll see a rather succinct explanation from the Eurogenes author, as follows:
So, just breaking down "Davidski's" own statements:
1. R1a-Z93 (Indo-Iranian), R1a-Z282 (Balto-Slavic/Norse), and R1a-CTS4385 (Germanic) appear to expand during the Copper age.
2. Where did these expansions take place from? "Davidski" says he doesn't know.
3. He states that the expansions occured at about the same time that the European genetic structure shifts from "Sardinian-like" to "Eastern European-like".
I've stated this before, but it is readily apparent in looking at the Lazarides PCA, above, that Europeans did not shift from being "Sardinian-like" to being "Eastern European-like." More correctly, they shifted from being "Loschbour-like", "Sardinian-like" and "Scandinavian Hunter-Gatherer-like" toward populations in the East (anywhere between Poland and the Levant.)
Davidski doesn't mention an R1b rich population as a potential source for the Copper Age shift, probably because R1b doesn't look like a dominant population on the Copper Age Steppe.
There is R1, R2, Q, and P DNA on the Steppe, that is true. But with the R/Q/P split happening more than 25,000 years ago, it's problematic to be inferring from this, a "source" for Copper Age R1a. After all, "Q" got all the way to Central America with just dogs in 15,000 years. So what's with thinking that R1 lineages were simply confined to the Central Eurasian steppe for 20,000 years (and not to Europe until the Copper age) ?
There definitely is a shift of modern Europeans between the Mesolithic and today. I agree with that.
But I don't agree that the shift happened due only to replacement from the Ponto-Caspian or Central Eurasian Steppe and only during the Copper Age.
It's just as likely that the genetic shift of Europeans is due to Western Europeans fusing with populations of Finland, Scandinavia, the Baltic, Balkans (including Greece), Central Europe, the Ukraine, Russia, Anatolia, and the Levant, starting in the Mesolithic and continuing to the present day. It would have been a complex process, with waves of people possibly moving both in and out of the Steppe and in and out of Europe, since the R/Q/P split.