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.