"certain European populations have a mutation that causes lactase to be produced throughout their lives". Lactase persistence is interesting. There has been selection pressure for persistence in Northern European (eg: about 98% of Irish people have lactase persistence) populations but not in Southern Europe (under 40% in Italy) and one might even say "almost selection against" in Asia (under 10% in China). Apparently, the gene first evolved in the Near East, possibly tied to first domestication of the auroch and then spread radially from there into Europe. Convergent evolution, ie: lactase persistence using different genes, also came about in the Bantu population in Sub-saharan Africa which enabled this population to spread further south and overtake San populations (bushmen). Perhaps this is the same selection pressure in action.