There is a new paper out comparing the Neolithic expansion of y haplogroup R1b in Europe to that of Y haplogroup E1b1a in Africa.Modeling the contrasting Neolithic male lineage expansions in Europe and Africa
We have identified demographic scenarios that can lead to the contrasting phylogenies observed for the major Y-chromosomal lineages that expanded during the distinct Neolithic transitions in Europe and Africa. These suggest that in Europe, the R1b lineage experienced an extremely rapid and extensive increase as soon as it entered the continent, expanding more than a thousandfold in a few generations. The expansion in Africa began from a larger population size, took thousands of years and ended only recently.
If we had used the more likely 4 to 5 KYA estimate of the R1b TMRCA from the rho statistic , the expansion in the current model would have been placed close to this time, well within the Neolithic and, interestingly, also close to the time of establishment of the major European mtDNA haplogroup, H, approximately 6 KYA [7,8]. The rapidity of the R1b expansion and the large increase in population size are most consistent with migration and population replacement, issues debated by archaeologists but favored by the aDNA data [5-9].
This paper was brought to my attention by Heber over in the L21 subforum.