Nature has just published a paper on the discovery of a European-specific subclade of R1a, defined by the M458 mutation and classified as R1a1a7. It's a long-awaited and ground-breaking result, because structure within R1a has been poorly understood to date, despite the fact that it's one of the most dominant Y-chromosome haplogroups in Europe and Asia. The data included in the study point to what is now Poland as the most likely place of origin for R1a1a7. Here's a nice map...


Let's assume then, that R1a1a7 has only been around for 4,000 years or less. If so, that would make it a perfect candidate for a paternal marker of the proto-Slavs, who probably originated in what is now Southern Poland and began expanding during the late Iron Age. Their descendants eventually settled across much of Central, Eastern and Southeastern Europe, but rarely in Scandinavia, which correlates well with the current spread of R1a1a7.
The paper also claims that it's unlikely that there were any major post-Neolithic population movements from Eastern Europe to Asia, because R1a1a7 is today basically missing east of the Urals. But what if a different, as yet undiscovered subclade of R1a migrated from Europe to Asia before R1a1a7 had a chance to expand? Ancient DNA results do suggest that Europeans carrying R1a migrated east via the Russo-Kazakh steppe as far as South Siberia during the Bronze Age (see here), but this information was ignored by the authors.
So well done on finding the new R1a subclade, but there's obviously something off about its age/expansion estimates. When will that change I wonder?
References...
Peter A Underhill et al., Separating the post-Glacial coancestry of European and Asian Y chromosomes within haplogroup R1a, European Journal of Human Genetics advance online publication 4 November 2009; doi: 10.1038/ejhg.2009.194
T. Lappalainen et al., Migration Waves to the Baltic Sea Region, Annals of Human Genetics, Volume 72 Issue 3, Pages 337 - 348, doi: 10.1111/j.1469-1809.2007.00429.x
Update: R1a1a7 is now known as R1a1a1b1a1. See here.