[MEGoody]

But when cattle were first domesticated 9,000 years ago and people later started to consume their milk as well as their meat, natural selection would have favored anyone with a mutation that kept the lactase gene switched on.

Why would 'natural selection' favor someone who could drink milk?

[Alter Kaker]

Why would 'natural selection' favor someone who could drink milk?

Because it's a food source. People who couldn't drink milk had less food to subsist on and were less likely to survive.

[muawiyah]

This is not "natural selection" in the sense of which tigers or wolves ate which people, but rather how long the females stayed in good health to breed more babies than the others who couldn't drink cow's milk.

Although we've come up with the term "cheese eating surrender monkey", it's actually the case that those who can eat fresh cheese will probably outlive those who can't.

(NOTE: aged cheese has little if any lactose).

[labette]

"Why would 'natural selection' favor someone who could drink milk?

I would think the casualty rate would be kinda high if milk consumption was attempted before domestication.

[null and void]

Why would 'natural selection' favor someone who could drink milk?

It's an additional food source in a famine. Being able to drink milk could easily be the the difference between life and death.