The most obvious example of this is lactose, the sugar in milk. Some 10,000 years ago, before humans started farming, no one could digest this beyond a few years of age.
But today, the rate of lactose tolerance in different parts of the world is a clue to the different histories of farming across the globe. While 99% of Irish people are lactose tolerant, in South-East Asia, where there is very little tradition of farming, the figure is less than 5%. FULL ARTICLE