on grain agriculture it's true. However, just because it allowed the formation of early cities doesn't mean eating it was good for us. At best it sustained us.
Up until very recently in human history there was no civilization, and humans were primarily nomadic. Since we didn't stay in any one place very long, we did not eat anything which was not already growing wild where we settled. A few short thousand years is not enough time for human physiology to adapt to a food source which was alien to it for many many thousands, even hundreds of thousands of years prior.
We don't eat hay, ruminants do since they have the gut bacteria to digest it, so that is a nonsense argument. Many animals today are adapted to eating grasses, but only one significant group has adapted to eating grains: birds.
Grains are not fruits or vegetables; they don't want to be eaten, they want to scatter and blow on the wind. As such, they are full of defensive proteins (gluten is just one of these) as well as anti-nutrients such as phytates, which actually prevent mineral and nutrient absorption in humans.
The most likely reason the prevalence of grain intolerance is increasing is because the amount of defensive protein in todays hybridized and chemically mutated grains is much higher than it was even 50 years ago. New never before seen, potentially toxic proteins have also appeared and are sold directly to us without any sort of testing.
But don't take my word for it. Just ask anyone who has adopted the Paleo or Primal lifestyle how they feel. They will probably tell you they feel like they've gotten their lives back after giving up a chronic toxin.
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