For one thing, Zuk points out, we are still evolving. “Evolution is this kind of meandering, stumbling path — and even calling it a path isn't good because that suggests you're going from point A to point B. And there is no point B.” For another thing, there was never a time when we were absolutely perfectly adapted to our environment. At the risk of stating the obvious, Paleolithic people had problems too. This was not an idyllic time when we lived in perfect harmony with the Earth and the food chain.With the caveat that she’s not a psychological expert, Zuk can’t help but note there’s a clear element of nostalgia in the Paleo movement: “This feeling like things used to be better, things used to be simpler, things used to be easier.” And of course, the farther back you go, the easier it is to blur the lines of reality and see life through nostalgia’s misty lens. It makes the Paleo premise seem all the more arbitrary. After all, why stop there? If things get better the farther back you go, then, adds Zuk, “Why wasn’t our life on the Savannah an endless yearning to get back to being in the trees?”There’s no question that many elements of contemporary life clash with our bodies from a physical standpoint. “I do recognize there are issues of scale,” says Zuk. “For example, wearing stiletto shoes and walking on concrete all day long is not how our muscles were meant to function.” But it doesn’t follow that we should all do the exact opposite and go barefoot. (That’s another Paleo-esque belief that’s not as simple as it sounds .) Of course, there are versions of stiletto shoes in modern foods as well. “Living on Coke and Cheetos all day is going to be bad for our physiology, because that’s not how our physiology evolved to digest food,” Zuk says. But acknowledging that fact, “is not the same thing as saying we need to act exactly like we acted on the Savannah.”When faced with that argument, Zuk finds that some Paleo advocates tend to walk it back. “They say, ‘Well, we're not really saying you have to eat exactly like people ate then. We're just saying you shouldn’t eat all these highly processed foods.’” Clearly, the Paleo diet is a lot more specific and extreme than just avoiding processed foods, but even if that was the basic premise, it’s hardly a novel concept. “A lot of people will tell you that,” says Zuk “It has nothing to do with being a caveman.”Setting aside the historical veracity of Paleo, nutrition professionals echo similar concerns. “I don’t believe the Paleo diet claims are valid,” says Natalie Butler, RD and senior advisor to the online medical resource Healthline . Like Zuk and Warinner, she points out that some of the basic principles (like reducing highly processed foods) may promote better health in some people. However, “it does exclude proven healthful foods like legumes and potatoes that provide many important nutrients, especially fiber and complex carbohydrates.” She adds that there’s no evidence to indicate that “going Paleo” leads to better health in the long term.We do know that Paleo can be dangerous or even life-threatening to some. Butler points out that a high-protein diet is linked to pregnancy complications, preterm delivery, and fetal health risks. Children and infants shouldn’t be put on this regimen either, though many in the Paleo movement do advocate for “ cave babies .” Last year, Australian celebrity chef Pete Evans’ cookbook was put on hold by the publisher after health authorities called out his baby-formula recipe, which contained toxic levels of vitamin A. “In my view, there’s a very real possibility that a baby may die if this book goes ahead,” said Heather Yeatman, president of the Public Health Association of Australia.Dr. Cordain evidently disagrees. At least, he wouldn’t go so far as saying anyone shouldn’t go Paleo. “People with pre-existing kidney disease should have their nephrologist monitor their condition anytime they increase the protein content of their diet,” he replied when I asked if there were any health concerns to consider. “Ironically, it may be the refined sugars, grains and high glycemic load carbohydrates that may underlie their kidney disease,” he concluded. So, in his opinion, it’s not the Paleo diet that presents a risk to those with kidney problems. It’s that they weren’t eating that way in the first place.In terms of dubious nutrition, Paleo is no more problematic than any popular diet trend. “Pretty much any diet that either demonizes or glorifies one particular food is not going to be a good idea,” says Zuk. I wouldn’t expect Dr. Cordain to cede that point. But I did want to know his take on all the evolutionary holes that others have poked in his theory. In conclusion, I asked how he’d reply to people like Zuk and Warinner, who criticize the very premise. His response, in its entirety:"'Nothing in biology makes sense except in the light of evolution'" — Theodosius Dobzhansky , 1973. A similar statement could be made: Nothing in nutrition makes sense except in the light of evolution."Like so many diet fads, it sounds like common sense. But the science of human evolution and biology is simply more complicated than our common knowledge. It can’t be broken down into seven basic principles or delivered in a handy list of “the foods you were meant to eat.” Any of these experts will tell you that even if we were meant to eat a Paleolithic diet, even if there was just one Paleolithic diet, and even if that diet included, for example, broccoli — that broccoli would be an extremely different vegetable than one you could buy at a store today. For one thing, it wouldn’t exist. Broccoli wasn’t cultivated until approximately 2,500 years ago . Does that make it unhealthy? Of course not. Not even Paleo devotees believe that. In fact, look it up on their food lists and you’ll find that, yes, broccoli is Paleo — though it’s not Paleolithic.This is what I find so concerning about this concept of Paleo as a lifestyle, rather than a diet trend. When, as a culture, we recognize something as a fad, we also recognize that it will likely fade. Elevating “Paleoism” to the status of a lifestyle gives it a sense of age and authority. It indicates a basis in ethics or beliefs, up there with veganism or keeping kosher. Regardless of our individual stances, we respect those who follow those practices (or we ought to).But Paleo isn’t based in ethics or faith. It’s based on a false idea of who we once were and who we are now.