Quote from prior post: "can't imagine that a group of isolated "R1b" men took over the land and virtually eliminated all men AND at the same time kept the rest of the population with its specific ancestral background."
My thoughts are that since most diseases would affect males and females the same I think this cause is ruled out.
Some think, as some do about the Anglo-Saxons in England, that certain male groups were preferred socio-economically and even by the legal system.
Of course, the easiest reason to imagine is a male fought war where a lot of males one side died and a lot on the other side prospered.
I think there are known, documented examples of this. In the Caribbean Islands you find this. http://www.familytreedna.com/public/CubaDNAProject&fixed_columns=on
Compare the Y DNA results versus the mt DNA results. Under Y, you see predominately European HGs, including J and I and as you'd expect, R1b1b2. I saw some African, but I think only one Q, which would be Native American. That figures to about 1% Native American on the Y side.
On the other hand, flip over to mt and you'll see quite bit more continental mix. Lot of European H, etc., a number of African AND quite a bit of A, B, C & D, which is Native American. I calculate roughly 30% Native American on the mt side, but generally much better balance overall between the continents with more African as well.