 The variation for light skin colour was introduced to Europe by the neolithic farmers.After the arrival of the neolithic farmers, a SLC22A4 mutation was selected for, a mutation which probably arose to deal with ergothioneine deficiency but increases the risk of ulcerative colitis, coeliac disease, and irritable bowel syndrome.The Bronze Age saw the development of long-distance trading networks, particularly along the Atlantic Coast and in the Danube valley.