I just read last night that 80% of Europeans have DNA that was already in Europe before the Last Glacial Maximum (LGM), 23,000-18,000 years ago. Very little was contributed by the migrant agriculturalist. The LGM was the coldest period during the Ice Age.
this?
British Have Changed Little Since Ice Age, Gene Study Says
http://news.nationalgeographic.com/news/2005/07/0719_050719_britishgene.html