Dienekes commented on a new study by Bramanti et al. in his blog, which suggest that Central European farmers are not descended from local hunter-gatherers.

I was quite excited when I started reading that they analysed the DNA from both ancient Central European hunter-gathers and farmers. I wondered if they had tested autosomal DNA to assert that the two populations remained segregated, with no or very little genetic admixture. In fact, there was no autosomal DNA and not even Y-DNA, but just mtDNA. That's a little disappointing to say the least. Besides they only tested 22 hunter-gatherers and 25 Neolithic farmers, so that is certainly not very representative of the whole of Central Europe over ten millennia or so.

It is nevertheless interesting that 18 out of the 22 hunter-gatherers belonged to mtDNA haplogroup U, including 14 to U5 and two to U4. The four individuals belonging to other haplogroups (J, T2e, K) were all from the same site (in Ostorf) and so could be a special case of early admixture, or a different ethnic group of hunter-gathers.

The overwhelming dominance haplogroup U among Mesolithic Europeans points at a relative genetic homogeneity of pre-agricultural Europe. This is consistent with a Nomadic lifestyle and geographic isolation during and immediately after the last Ice Age. U5 is also the haplogroup of the 9,000-year-old Cheddar man from Britain. From the limited data available it appears that U5 could have been the main mtDNA haplogroup of Mesolithic hunter-gatherers at least from Central to Western Europe.

Haplogroups confirmed to have been present among the early Near Eastern farmers are N1a (from another study), HV, H, V, J, T, K and U3. It is almost undeniable that the Y-DNA of these early farmers were predominantly E-V13 and J2b (and possibly G2a).

This still leaves us wondering about the origin of haplogroups I, W and X. My guess based on the current distribution is that W and X came later from the East with the Indo-Europeans (Y-DNA R1a and R1b), while mtDNA hg I could have been present among Scandinavian hunter-gathers (along with Y-DNA I1, as opposed to Y-DNA I2 for the rest of European hunter-gatherers).