I’ve long found the Paleo Diet plausible, but I can’t quite agree with its premise:
The primary tenet of evolutionary medicine is that the profound changes in the environment (e.g., in diet and other lifestyle conditions), which began with the introduction of agriculture and animal husbandry approximately 10,000 years ago, occurred too recently on an evolutionary timescale for natural selection to adjust the human genome.
Evolution doesn’t occur on a geological time scale because it’s a glacially slow (and steady) process, but because there’s rarely a need and opportunity to change in a big way.
If an omnivorous species finds that it can’t hunt prey animals and gather varied plant foods anymore, but it can eat grains, that is a huge new selection pressure. A few hundred generations is plenty of time to evolve a response to that. After all, one generation will cull the herd quite a bit, and it only takes a few generations to artificially select a new breed of dog or cow.
The issue with humans, as I see it, is that the most successful humans, for thousands of years, were those who held onto the hunter-gatherer diet and some of the hunter-gatherer lifestyle by becoming aristocrats — don’t poach the king’s deer! — and lording over the poor peasants, who had to subsist on a monotonous diet while performing monotonous labor.
Evolutionarily, it’s good to be the Khan, and that means that only some humans faced strong pressure to adapt to agriculture, while others retained the old ways and did not face that strong pressure to adapt to agriculture — they faced strong pressure to succeed at war. Then their downwardly mobile descendents ended up as farmers and tradesmen, where aristocratic traits weren’t so adaptive.