Alex V. answered • 02/05/21
PhD student with lab experience and 5+ years of teaching experience
It's surprising because the Hadza come into contact with many animals and other groups that herd animals that produce milk. As such, one would expect that because milk is a good source of nutrients, those Hadza that were able to digest lactose and thus get more nutrients from milk, would have better nutrition and be healthier, have healthier children, etc. By being healthier and having more and healthier children, they would pass this trait on to their relatively more numerous descendants and you'd expect the trait to proliferate in the population. But it's surprising that this isn't the case!
