Critics often lambast the Primal Blueprint and other ancestral/paleo ways of eating for what they see as fatal flaws:

First, that we don't know what our ancestors were truly eating.

Second, that there wasn't just one paleo diet.

Third, that even if we could know exactly what our ancestors were eating, it doesn't mean those foods were the ideal foods; they were trying to eat whatever was available, not whatever was most nutritious or synergistic with their genome.

Before I address these, I want to make an important point. The anthropological record provides a framework for further examination of nutritional science; it does not prescribe a diet. It gives us somewhere to start so we're not flailing blind men dropped off in the middle of a strange city. That is why we're interested in what early humans ate (and didn't eat).

It may surprise you to know that I think the first assertion is absolutely right. We don't know exactly what our ancestors were eating. There are no pleistocene food journal entries scrawled on a cave wall someplace, and many of the primary sources we can access - phytoliths (which indicate the presence of vegetal material) and stable carbon/nitrogen isotopes (which indicate the source of dietary protein) - require analysis and interpretation, thus becoming secondary sources. If you thought food frequency questionnaires were unreliable, try figuring out if the phytoliths found on Neanderthal dentition originated from the direct consumption of plants or the consumption of fermenting plant inside a recently hunted animal's stomach, or whether the isotope analysis of African hominins from a few million years ago indicate diets high in grass seeds or diets high in grass seed-eating herbivores.

However, we absolutely do know what early humans did not eat: We know these things because these foods either didn't exist until the late 1880s (seed oils like corn) or only graduated from expensive luxury item to widely-used staple food in the 1700s (white sugar).

As to the second claim, of course there is no one true ancestral diet with a strictly curated, specific list of dietary DOs and DON'Ts. Humans have managed to populate every barely hospitable nook and cranny of this planet. If living things grow, slither, crawl, flap, swim, or otherwise reside there, we will set up shop in order to eat them.

However, patterns do emerge. First, there's the aforementioned total absences - seed oils,sugar - plus a dearth of cultivated grains. Wild versions of grains existed (after all, the first agriculturalists needed something to domesticate), but there's little evidence to suggest they were major parts of most early human diets.

Second, there's animal consumption. We just love eating sentient, mobile organisms. There's never been a traditionally vegetarian culture, and every hunter-gatherer population ever studied consumes animals (PDF).

Third, there's plant consumption. Plants are trickier than animals because they keep fighting back after you've killed (and sometimes cooked) them.

There are other patterns, which I'll discuss in future posts.

The third charge is a common one, and it takes many forms. The one I get a lot is that early humans were desperate scavengers, just barely skating by and eking out a diet of diseased rodents, chitinous bugs, tree bark, and lichen. Since he didn't "know any better" and was just eating what he could without regard for nutrients, what early humans ate shouldn't inform our dietary choices. Well, it's a specious argument. Whether our ancestors were dumb brutes stumbling through life without ever considering what they ate (they weren't) or unaccredited ethnobotanists with intricate knowledge of medicinal, toxic, and nutritious plants and animals (they probably were) doesn't matter in the slightest.

Let's say that natural selection adapts an organism to a given environment by selecting for an advantageous trait. What if the environment shifts, as they do, and the trait the original environment selected no longer works the same way? This is an evolutionary mismatch. It can happen with any environmental shift, like a change in diet.

Mismatches between an organism and its environment are core concepts in evolutionary biology. They aren't controversial. In fact, evolution requires evolutionary mismatches, because mismatches represent selective pressures on an organism that lead to adaptations (which of course lead to more mismatches, and so on).

It's easy to see how diet fits in: if environment shapes an organism's evolution (via natural selection and evolutionary mismatch), and diet represents an aspect of the environment, then diet (in addition to many other environmental factors) must affect how an organism develops. I don't see how you can argue against that. You can argue that this specific food was or wasn't part of the ancestral dietary environment, or that Grok had no idea what he was doing, but you can't argue against the relevance of the ancestral dietary environment.

There were no "ideal foods"? Okay. That's not the point. I'm just establishing that there were simply "dietary patterns that shaped the metabolisms, nutritional requirements, endocrine systems, and brains of the walking, talking, loving, pondering collectives of cells and microbes we call ourselves."

I don't know about you, but it seems like examining these dietary patterns might offer helpful clues for modern humans currently embroiled in a classic case of evolutionary mismatch. Mismatches are very interesting when you're a detached academic observing the trajectory of another species, but on the ground level, to the organism experiencing it, mismatches lead to diseases, pain, and suffering. They're awful.

Luckily, there's evidence that dietary changes are relevant. When zookeepers noticed the gorillas were getting diabetes and heart disease on scientifically-formulated gorilla chow, they said, "Hey, let's try providing a diet approximating the one these great apes might eat in the wild. I'm thinking leafy greens, alfalfa, green beans, and tree branches." The gorillas thrived. So did the grizzlies and the elephants when placed on diets that approximate (rather than replicate) their wild diets.

Are we so different?