Why are so many people of asain descent lactose intolerant?
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Most mammals actually become lactose intolerant after they stop weening. You need an enzyme called lactase to digest dairy and most mammals stop producing that as they get older. Amongst humans, 65% of adults are lactose intolerant, so the real question is why can some people digest lactose after they’ve grown up?
We’re not really sure. I’ve seen speculation that thousands of years ago, there was a famine that forced people to drink milk for sustenance. The people who had an ability to digest milk had an advantage, so natural selection favored them during the famine. And it probably wasn’t one famine. Lactose tolerance seems to have evolved around 4 times independently in different populations.
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