Whenever an article about the paleo diet is published in a major newspaper, at least one commenter expresses dismay that paleo dieters don't realize that humans are adapted to grains and milk. That's a misconception on several levels. First of all, plenty of us are educated enough to know that genetic adaptations can occur rapidly. I remember in high school when I first read The Beak of The Finch, which is about the finches in the Galapagos islands and how their populations genetically respond rapidly to changes in the environment. It takes down the myth that evolution is slow and can't be observed.
In that case, why are we still talking about what our ancestors eat as if it matters? Well, so far the evidence is that some adaptations have occurred in some populations response to neolithic food. Genetic evidence shows that most of the population in modern societies is descended from agriculturalists who had been farming for several thousand years. Clearly, our ancestors were very much able to survive on diets of grains and dairy.
I was just reading this scientific paper, Demeter's Legacy, which is free online and a fascinating read. Yes, there are two major genetic adaptations in agriculturalist populations. One improves the digestion of starch and the other of dairy. Great, we can eat these foods and reproduce. Yay, but it doesn't mean that we are completely adapted to them. There are plenty of foods that are digestible for everyday needs, but damaging in the long term. It's up to us to do the research and figure out if foods are really worth it. I ate bread for most of my life and felt OK, but life for me is not just about surviving, but about thriving. It's important to remember that even though adaptations have occurred, the vast majority of our genes were forged before agriculture.
And for people descended from more recent hunter-gatherers, neolithic foods are even more devastating.
I created a list that I am currently still adding foods to which outlines some pros and cons of various foods from the paleo viewpoint. I think foods should be judged on their merits and there is no "one true" paleo diet...there can't be, since last time I checked I couldn't get wild antelope at the grocery store. It's about learning from the wisdom of the past and choosing food based on those principles, not reenactment.