Milk Does a Body

Evolution of Adult Lactose Absorption

Farming, cheese, chewing changed human skull shape
Aug 2017, phys.org

The agricultural revolution put the human genome in the spin cycle of a washing machine. Plants, though fibrous, are easier to chew than animals. So during the thousands of years while we were discovering the magic of seed-sowing, and eating the results of our pre-science experimentation, our bodies (our jaws especially) were changing in response.

At this time in our development, the rate of change for a genome was equal to the rate of change of our culture, and our diet, and so the two were able to influence each other. Nowadays, those rates have changed so that our culture moves faster than the genome - i.e., just this week we saw the first 'living drug' that changes the patient's genome so that it attacks cancer.

Anyway, this is our history:

The largest changes in skull morphology were observed in groups consuming dairy products, suggesting that the effect of agriculture on skull morphology was greatest in populations consuming the softest food (cheese!).
-phys.org

I just have to rant for a moment about arguments for an extreme vegetarian diet. I'm all for being healthy and eating more vegetables and less animals, but to say that it is not natural for us to eat meat or dairy products is preposterous, and this is one of those reasons why. Furthermore, to conjure support for the rational adoption of a 'paleo' diet that mimcs the caveman's diet, because 'that is the diet that we evolved to eat', is also preposterous. A lot has happened since caveman days. Sure, the homo sapien is (?) years old (let's just say on the order of 100,000 years). But since that time, our genome has continued to change. Dairying practices are not 100,000 years old, but more like 10,000. And the impact this had on the homo sapien genome was tremendous.

We are the only mammal that maintains lactase into adulthood - that is a genetic modification that we did to ourselves. Nature did not do that to us; we did it. According to this article above, we also changed the shape of our skulls because of eating cheese.

So, in short, we are  complex creatures. We are more complex than any new diet can encapsulate. I'm not trying to tell anyone what to eat up in here. But I am saying that instead of asserting that there is something wrong with the way we are, and that we should try to be more like the way we were, the "natural way", is to ignore the unfathomably complex and epic journey we have made as a species, and that we should continue to make, as long as we don't all kill each other, and as long as the planet that gave us life doesn't go and kill us all.

Post Script
Here's a paper on lactase persistence, perhaps the greatest story in human culture ever, because it was the inflection point beyond which our culture moves faster than our genes can keep up with.
Evolution of lactase persistence: an example of human niche construction, 2011