Terms like “the paleo diet”, “primal lifestyle”, “evolutionary fitness”, and “ancestral health” all operate under the shared premise that our evolutionary past is the key to understanding how to be healthy today. While I certainly don’t agree with any movement that has one size fits all recommendations, I do agree that this premise is an important place to start from. However, it can also be a dangerous place to start from because naive reasoning without evidence can easily lead us astray (we all fall victim to this to some degree). Nonetheless, understanding how and why we evolved the way we did is one key to understanding how we can be healthier and live better today.
I recently finished reading The World Until Yesterday (a book I enjoyed more than I thought I would) which focuses on what we can learn from traditional societies in terms of our health, social relations, conflicts, child-rearing, and treatment of the elderly. As Diamond puts it in the book: “All human societies have been traditional for far longer than any society has been modern.” Even though I don’t agree with everything he wrote, I think Diamond makes a compelling case that we can learn from studying our hunter-gatherer ancestors (even though he doesn’t really advocate a paleo diet per se).
This seems like a reasonable starting point and many evolution enthusiasts share this belief. If one were simply to consider the fact that most of our species’ existence has been spent as hunter-gatherers it would seem that we have much to learn from our ancestors in terms of how to live well, both biologically and culturally. But is this so, or is this a Paleofantasy? 
The paleo diet theory, then, seems to make sense until one examines the evidence. If human evolution is accelerating, as the evidence shows that it is, then it doesn’t matter how long we ate a “paleo diet” for — what matters is what we have now adapted to eat. Then again, let’s not rush to dismiss the paleo diet (and its many variations) simply because some populations have adapted to tolerate grains. Maybe the paleo folks have a point, i.e., just because something is edible it doesn’t necessarily follow that it’s also an optimal (or even good) source of nutrition.
The real issue here is that when you think about it, paleo logic can fail us in terms of how we think about both health and culture (largely due to the narrative fallacy). This makes any sort of dietary advice very difficult to give because certain populations have adapted to eat certain things that others haven’t. The implication is, of course, that there is no such thing as a one-size-fits-all optimal diet for everyone.
Paleo Logic is a good a starting point, but when something sounds nice in theory and doesn’t hold up empirically, then I’d suggest ditching the bogus theory.
 See The 10,000 Year Explosion.