Lactose tolerance a key to evolution?

No, I’ve never seen any references to this. I could flippantly suggest that the US, UK and many other developed countries, which are in the grip of an obesity epidemic, are examples.

There are well documented examples of the opposite effect though. There’s an area in Japan where the population consumes less (about 20% less) food than the Japanese average because of cultural reasons. This group has a higher than normal population of oldies reaching the 100 year mark.