Lactose Intolerance: An Ancestral Trait

Dr. Sarah Tishkoff discusses lactase persistence. (1:58)

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  • The enzyme lactase digests lactose, the sugar in milk.
  • The lactase gene is active in infants, and they are lactose tolerant.
  • After weaning, humans stop producing lactase and become lactose intolerant.
  • Some people carry a mutation that keeps the lactase gene switched on past infancy, resulting in what is called lactase persistence or lactose tolerance.