There is an interesting report on Day 2 of the recent 2013 Family Tree DNA Conference here
, in which Dr. Michael Hammer addressed the changes in thought among geneticists regarding R1b in Europe.
Here is a quote from the article that seems particularly appropriate for this thread.
. . . This evidence supports a recent spread of haplogroup R lineages in western Europe about 5K years ago. This also supports evidence that P311 moved into Europe after the Neolithic agricultural transition and nearly displaced the previously existing western European Neolithic Y, which appears to be G2a.
This same pattern does not extrapolate to mitochondrial DNA where there is continuity.
What conferred advantage to these post Neolithic men? What was that advantage?
Dr. Hammer then grouped the major subgroups of haplogroup R-P3111 [sic] and found the following clusters.
U106 is clustered in Germany
L21 clustered in the British Isles
U152 has an Alps epicenter . . .