See http://www.nature.com/news/archaeology-the-milk-revolution-1.13471 http://www.nature.com/news/archaeology-the-milk-revolution-1.... Lacose tolerance apparen

See http://www.nature.com/news/archaeology-the-milk-revolution-1.13471 http://www.nature.com/news/archaeology-the-milk-revolution-1.... Lacose tolerance apparently allowed middle-eastern nomads to wipe out and replace the native european hunter-gatherers, and set up an agricultural society in their place. "In a 2004 study, researchers estimated that people with the mutation would have produced up to 19% more fertile offspring than those who lacked it. The researchers called that degree of selection “among the strongest yet seen for any gene in the genome”."