Increasingly, it looks as if the hunter-gatherers who lived in Europe at the end of the ice age have been largely replaced. Judging from all those U5 mtdna results from ancient skeletons, I’d say that the hunters don’t account for more than 10% of the ancestry of modern Europeans. It looks as if something similar happened in the Bantu expansion: modern Africans are mostly not descended from the hunter-gatherers who lived in those same places a few thousand years ago. The same could be said for south-east Asia, Indonesia, and the Philippines. Farmers spread, more than knowledge of farming.
In part, this may be explained by a kind of first-mover advantage. If a population has already farmed for a couple of thousand years, they should already be more adapted to that ecological niche: in terms of metabolism, immune system, and psychology. So if a few boatloads of Anatolian farmers land in a hunter-gatherer Italy, they will be better at farming than the locals _can_ be. They will be less prone to alcoholism, will have more resistance to crowd diseases, will be better at living a relatively boring way of life. Their population will grow faster than that of the local hunters, even if the hunters are trying agriculture. Extrapolate that trend for a few centuries and they dominate.
West Hunter 
Greg,
We see high incidences of the U5 haplogroup both before and after the transition to farming from hunting/gathering/fishing. This was the conclusion of a study of 92 Danish human remains that ranged in time from the Mesolithic to the Middle Ages. The study found genetic continuity from late hunter/gatherer/fishers to early farmers:
“The extent to which early European farmers were immigrants or descendents of resident hunter-gatherers (replacement vs. cultural diffusion) has been widely debated, and new genetic elements have recently been added. A high frequency of Hg U lineages , especially U5, has been inferred for pre-Neolithic Europeans based on modern mtDNA data, with Hg U5 being fairly specific to Europe. […] Our study therefore would point to the Early Iron Age and not the Neolithic Funnel Beaker Culture as suggested by Malmstrom et al. (2009), as the time period when the mtDNA haplogroup frequency pattern, which is characteristic to the presently living population of Southern Scandinavia, emerged and remained by and large unaltered by the subsequent effects of genetic drift” (Melchior et al., 2010)
Thus, the sharp genetic divide was not between late hunter/fisher/gatherers and early farmers. It was between the earliest farmers and groups that had been farming for at least a millennium or so. The evidence points to natural selection and not to population replacement.
But isn’t mtDNA unresponsive to natural selection? That’s what I used to think. There is growing evidence, however, that some mtDNA loci can change in response to natural selection. In particular, some haplogroups seem to reflect a tradeoff between thermogenesis and ATP synthesis. If true, the decline of U-type haplogroups among early farmers may reflect the different patterns of physical activity between them and hunter/fisher/gatherers.
References
Melchior, L., N. Lynnerup, H.R. Siegismund, T. Kivisild, J. Dissing. (2010). Genetic diversity among ancient Nordic populations, PLoS ONE, 5(7): e11898
An interesting post, an interesting comment: when are the Forces of Progress going to intrude to Stop That Sort of Thing?
“They will be less prone to alcoholism”
Tell that to anthropologist Kate Fox.
Or you know, just ignore Robin Hanson.
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