Mr Red, your point is very interesting.
There was a programme on TV last night about the Mesolithic period and 'Doggerland', the North Sea land area between what is now UK and France, before the giant tsunami from Scandinavia cut us off from the rest of Europe (a sort of watery Mesolithic Brexit!).

The people that lived there were hunter-gatherers originally, but as conditions changed they turned to farming.
However, hunter-gatherer womenfolk often intermarried with farmers (who were considered to be one-up on the social scale!) No men did this though, they kept within the hunter-gatherer group.

I was most interested as, like you, I wondered about their evolution in diet and their digestion of dairy foods/milk.

My husband is from an originally hunter-gatherer tribe in Northern Ivory Coast and southern Mali. He has slowly adapted to be able to digest dairy foods. Other African peoples have farmed cattle for centuries (Masai for example) Others have remained as non-farmers (eg Baka, originally called pygmies, who live deep in the rainforests)

I believe there are other populations around the world who cannot successfully digest milk foods and are lactose intolerant (many Chinese, Asians etc).

I am from Irish/Scottish stock, and imagine that farming and milk production would have figured prominently in very early times in these areas.

What no-one has entirely evolved to tolerate are trans-fats,refined sugar, additives, artificial flavourings, preservatives and other chemicals!
By the way, can anyone explain how 'lactose intolerant' peoples manage to breastfeed their babies, presumably with...er...milk?