University debate: "Milk is for babies. Grow up." Vegan: "No other animal drinks milk after weaning. No other animal drinks another species' milk. An adult with a glass of milk is a biological mistake." Anthropologist: "What switches off in a mammal at weaning?" Vegan: "Lactase. The enzyme that digests milk sugar. In nature it shuts down. That's my whole point." Anthropologist: "In most of this audience it never did. Why?" Vegan: "A mutation." Anthropologist: "One?" Vegan: "I assume." Anthropologist: "At least four. Northern Europe, Arabia, and twice over in East Africa. Different peoples, different letters of DNA, same result. All inside the last 10,000 years, and every time among people who kept herds." Vegan: "A coincidence." Anthropologist: "It's one of the strongest marks natural selection has left anywhere in the human genome. The children who could drink it lived, and outbred the ones who couldn't, until it was most of a continent. You've called that unnatural. It's the only definition of natural we've got." Vegan: "Two thirds of the world is still lactose intolerant." Anthropologist: "And two thirds of the world worked out cheese, yoghurt and butter, where the bacteria eat the lactose for you. The Mongols took half of Asia on fermented mare's milk with barely a lactase gene between them." Vegan: "No other species does it." Anthropologist: "No other species has a cow. Blue tits spent half a century robbing the cream off British doorsteps. The only thing holding back the rest of the animal kingdom is thumbs." Vegan: "Evolution isn't a moral argument." Anthropologist: "You opened with nature. I've brought it into the room and now you'd like it to wait outside." Moderator: "Time. Refreshments are at the back." Anthropologist: "Is there milk?" Moderator: "Oat." [She looks at the vegan for some time.]