It varies from north to south in Europe. The more southerly you get, the lower the percentage of those who are lactose tolerant.
It’s interesting to read about. It really does seem to be a survival strategy. People lose lactose tolerance, particularly to cows’ milk, in childhood; presumably because they’re no longer nursing and no longer need it. But there are always some who retain it. If your tribe’s sole food source was meat and milk products (including cheese and all the other things people make from milk) you might not survive to pass on your genes if you aren’t lactose tolerant as an adult.
There are undoubtedly some other animal-dependent people in the world, like the Masai in Africa, who have developed lactose tolerance over the centuries. But by and large, Africans are not lactose-tolerant.
But as with lactose tolerance, one can’t help but wonder whether there are other, similar dietary things to which some are acclimated and some are not.
But returning to meat in our own diets, we need to remember that grain-feeding food animals is a fairly recent thing. The very advantage of most food animals is that they can produce high-quality protein by eating things people can’t eat, like grass in the case of cattle and sheep. Hogs are omnivorous, like people and bears. But part of the ancient advantage of raising hogs was that they can support themselves, or nearly so, by simply foraging on their own. One recalls that the Spanish explorers and conquistadors always brought hogs with them on their campaigns, precisely because they didn’t have to bring food for them. The hogs would just live off the land the Spanish went through. Those hogs also brought deadly diseases to the Indians, because some would always escape and hogs carry almost any human disease. But nobody knew that at the time.
But now, we feed grain diets to hogs and cattle to fatten them. Cattle typically get that in the last 80-120 days of their lives, but hogs get it from weaning on. That changes the fat content of the meat and the nature of the fat as well. The same is true of poultry. Chickens and turkeys will eat absolutely anything, naturally, and can support themselves by foraging, except that chickens can’t in the winter. But the poultry we now eat is totally grain-fed, with some additives of secondary animal products like powdered poultry factory viscera and feathers compressed with grain products into pellets.
I’m not sure that’s such a good thing. I remember years ago a hillbilly came to me asking if he could borrow some small amount of money to buy some piglets he wanted to raise to eat. I made a deal with him. I would give him the money to buy those and more, and would buy the grain. He would raise them. But the grain was only a supplement. He used to go around to all the dumpsters behind grocery stores and load up the fruit and vegetables the stores throw out. It’s a lot. He would bring a pickup load every day after work, for the hogs. So the hogs ate little grain. Their diet was mostly vegetables and fruit. I paid for the butchering and we shared the meat. Best pork I ever had, before or since.
But it’s not economical to feed hogs on vegetables and fruit unless you get it free. Too expensive. Unfortunately, some kind of new health regulations prohibited stores from allowing people to "dumpster dive’ even to feed hogs. So that was the end of that.