Can a single mutation spread through a population and species?
The simple answer is yes. I have tried to find actual examples. • Lactase. All babies can digest milk, human milk at least. They have a hormone called lactase that breaks down the lactose (sugar) in milk. But most humans lose that capability early in life: after all, why should humans have evolved to drink milk after they are weaned? “Lactose intolerance” occurs when there is no lactase to break down the milk, and people get stomach upsets and allergic-type reactions. Originally, all adult humans would have been lactose intolerant. Once humans domesticated animals, milk became theoretically available from cows (including yaks), sheep and goats, camels, reindeer, and maybe other species. But it wasn’t truly available except to babies, because adults did not produce lactase. Now here comes the mutation: a mutation that maintains lactase production after weaning. It’s a very simple mutation in theory, because it doesn’t produce any new biochemistry, it simply extends the time over which t
