The following comments on the validity of a evolutionary approach to nutrition are from an email that I wrote to an Objectivist philosopher skeptical of the paleo diet. (The email was sent many moons ago, and I only just found it again.) My comments stand pretty well on their own, I think, and I hope that they’ll be of interest to folks interested in thinking about paleo in a philosophical way.

I cannot point you to a single study that definitively proves the superiority of a paleo diet. For a hundred different reasons — most of which probably aren’t on your radar — such a study is not possible. (Gary Taubes and Mike Eades have written on that problem.) Nonetheless, a whole lot of smaller, more delimited studies (as well as well-established biology) support the claims made by advocates of a paleo diet. Plus, people report looking, feeling, and performing better — with improved lab values — on a paleo-type diet. Each of us has our own experiences and experiments to draw on too.

Hence, as I said in a thread on Facebook: “I think I’ve got very good grounds for saying that a paleo diet is (1) healthy for most people, (2) far superior to the diet of most Americans, (3) exceedingly delicious and satisfying, and (4) worth trying to see if you do better on it, particularly if you have certain kinds of health problems.”

I’m not claiming certainty, nor do I assume that my current diet is optimal. We have tons to learn about nutrition and health. Yet that’s hardly a reason to ignore what we do know — or to suppose that we can just keep eating however we please without experiencing pernicious consequences down the road.

Moreover, people are doing themselves harm by eating the standard American diet. In my own case, I was on my way to type 2 diabetes (based on my doctor’s blood glucose tests) and liver disease (based on a CT scan showing non-alcoholic fatty liver disease). We can’t assume that the standard American diet is a safe default just because it’s all around us — just as people shouldn’t assume that the standard American religion is a safe philosophical default.

To address your skepticism about an evolutionary approach to nutrition, let me ask you the following… Imagine that you were given a dog to care for, but you’d never seen or heard of a dog before. Would you say that the fact that dogs are very close relatives of wolves is irrelevant to the question of what you ought to feed this dog? Wouldn’t that evolutionary fact suggest that the dog needs meat, meat, and more meat — not tofu or corn or alfalfa?

That evolutionary inference certainly wouldn’t be the last word on proper diet for the dog by any stretch of the imagination. Yet that inference would help guide your inquiry into the optimal diet for the dog — and guide your feeding of him in the meantime. That evolutionary perspective would be particularly helpful if the government and its lackeys were busy promoting a slew of false views about optimal canine diet. Ultimately, it would help integrate and explain your various findings about canine nutrition, since the nature of the canine was shaped by its evolutionary history.

On this point, your comparison to evolutionary psychology is not apt. Evolutionary psychology is a cesspool. But that’s not because inferences from our evolutionary history are difficult, although that’s true. Evolutionary psychology is a cesspool because it depends heavily on some false philosophical assumptions — particularly determinism and innate ideas.

The same charges cannot be made against an evolutionary approach to nutrition. We know that every organism is adapted to eat certain kinds of foods rather than others. We know that human biology was shaped over the course of millions of years, during which time we ate certain kinds of foods but not others. That suggests the kinds of foods that we’re best adapted to eat. Moreover, we can see in skeletal remains that when people switched to other kinds of foods, particularly grains, they declined remarkably in basic measures of health. Then consider what know about the nature of wheat, including its effects on the gut. Top that off with the positive effects people experience — improved well-being, fat loss, better lab values, less autoimmunity — when they stop eating wheat. Then you’ve got a compelling case against eating wheat.

The evolutionary perspective is not merely a useful starting point in such inquiries, to be discarded with advancements in modern science. It’s relevant causal history: it explains why we respond as we do to wheat. That enables us to integrate disparate findings about wheat (and other foods) into a unified theory of nutrition. That’s hugely important to developing nutrition as a science.

  • Andrew

    As evolved biological animals, it’s bizarre to suggest we ignore evolution as it pertains to diet. At the same time, the passing dismissal of evolutionary psychology erodes your argument. Neck-down Darwinism is an inconsistent position.

    I do think some of the context from the piece to which you are responding would be helpful. It makes a difference if skeptics are questioning evolution itself vs. advocating 20th century nutritional reductionism (or other).

  • Gideon Reich

    Very well stated! And quite frankly I happen to agree on Evolutionary Psychology. Not that there aren’t some evolutionary components to the brain but as Diana pointed out, the kinds of conclusions typically drawn go far beyond reasonable evolutionary thinking. See Steven Pinker’s books for many things one could agree with, yet even more that I disagree with.

    • Andrew

      Criticisms of evolutionary psychology invoking determinism tend to be made by dilettantes (I use that term descriptively, not pejoratively). For general clarification, see “Evolutionary Psychology: Controviersies, Questions, Prospects, and Limitations.American Psychologist. 2010.

      There are also commonly problems and biases in conflating determinism with imprecise models of free will that undermine such discussions. While not the most definitive work on the topic, Sam Harris provides an approachable starting point and goes into some detail in his book on the topic.

      • Jennifer Snow

        Most evolutionary psychology claims are also made by determinist dilettantes, and the second or third-hand articles published by journalists are staggeringly bad, such as one I read that women may be “programmed” to prefer hairy men because hair may make it easier to detect insects on the skin and thus hairy men may be healthier . . . of course, this completely fails to explain why many human populations that live in insect-riddled conditions have next to no body hair. It could just be that women don’t give a crap about body hair and that cold conditions are more likely to activate our follicles to produce more and darker fuzz.

        If evolutionary psychologists want to be taken seriously, they should devote themselves to first understanding how and to what degree genetics and genetic expression affect human psychology before they start making claims.

        • Andrew

          When I seek to damn an entire field of scientific inquiry, my typical approach is to select the worst example of pop-science journalism I can recall from memory, and substitute that for the peer-reviewed papers of thousands of individual researchers. I agree, it’s much easier than selecting and critiquing a published paper actually representative of the field published by an actual scientist. Unfortunately, this tactic is correctly categorized as propaganda, and neither philosophy nor science.

  • Nick

    Why don’t you include the skeptic’s email?

    • Diana Hsieh

      Because it was a private email exchange between friends, and I didn’t think it proper to quote his words without his permission, let alone to publish his email address (!!).

  • Ray Audette

    Here’s the dog version of Paleo;

  • philosopher24601

    Just for the historical record, here is what the philosopher in question sent to Diana in response to the message above. The philosopher has no record of receiving a response. Surely a response at this point would be enlightening to all.


    First let me reiterate that I’m not skeptical that there is evidence for this diet. My main question is whether this evolutionary argument counts as evidence, or at least as significant evidence. If it doesn’t, then I think a lot more emphasis needs to be placed on the other kinds of evidence. I realize you’re not saying that the diet is a certainty. At best I think knowledge of a diet can count as a strong possibility. Just so it’s clear: a strong possibility is a working hypothesis that can and ought to guide one’s thinking and action in significant ways, so this isn’t dismissive of the hypothesis.

    There is much to say about your response. I could say more about why I think no dietary knowledge at this point could count as better than a strong possibility, but let me just focus on the status of the evolutionary argument, and the very excellent question you asked me about it. The question was fruitful because it helped me to clarify my views on this subject, and when I tried to answer the question, many of my suspicions were confirmed.

    > As for the evolutionary argument, let me ask you the following… > Imagine that you were given a dog to care for, but you’d never seenor > heard of a dog before. Would you say that the fact that dogs are very > close relatives of wolves is irrelevant to the question of what you > ought to feed this dog? Wouldn’t that evolutionary fact suggest that > the dog needs meat, meat, and more meat — not tofu or corn or alfalfa?

    I would say *yes*: if I didn’t know anything about dogs, and if I knew that dogs were descendants of wolves, then this evolutionary fact could provide evidence for what the dog should eat.

    But there’s a really important additional assumption here: knowledge of the evolutionary fact would provide this evidence, IF I already knew *what it is good for the wolf to eat.* If I knew that, knowledge of evolution would make knowledge of the wolf’s diet relevant to what the dog should eat.

    So, we do know that we are descended from Paleolithic human beings (I’ll call them “cavemen”). If we knew what was good for these people to eat, then this would be relevant knowledge to establishing what we should eat. It wouldn’t be definitively relevant (since some changes might have occurred to us since our descent from cavemen), but it would be highly relevant.

    So the important question is: do we know what was good for cavemen to eat, whether what they ate was best for their flourishing? Notice that knowledge about what is good for some organism to eat is knowledge of a causal claim. To say X is good for Y to eat is to say that eating X causes Y’s flourishing.

    We probably know a lot about what cavemen *did* eat (there’s only so much that would have been available to them). And knowing what they did eat is also relevant to knowing what was good for them to eat. Obviously what they ate was *good enough* for them to survive and reproduce and leave us as descendants.

    I do know about the evidence suggesting that cavemen were bigger and stronger than many modern human beings, which is *some* evidence that what they ate what was good for them. But notice that the evidence for what was good for them is evidence that is independent of the theory of evolution itself. That theory doesn’t tell us what our ancestors ate or that it was completely good for them, it only tells us (at best) that they are our ancestors, and that they ate something good *enough* to leave us as ancestors.

    Notice that the theory of evolution does not tell us that any adaptation is optimal. Evolution itself is not a goal-directed process. It is not true that any trait a being happens to inherit is optimal for its flourishing in an environment–it does not even mean the trait is “progress” compared to its ancestors. The traits we inherit from ancestors may be no good for our environment, and we may die off because of it. That’s as true for us as it was true for cavemen. It’s especially true for cavemen if they were, as Christian emphasizes in his post, rational men, and therefore in possession of free will. What they ate would have been a product of their choice as well, and could therefore have been a good or bad choice, depending upon facts about the nature of their life and environment. You could push the question back to pre-rational animals, but then if their diet was just a matter of preprogrammed behavior, this still does not mean it was optimal for them in their environment.

    So what kind of evidence would it take to know that the cavemen were eating an optimal diet, or one that was improved over their ancestors?

    I don’t fully know: it’s a complicated biological and medical question. It is complicated in large part because it’s a question of cause and effect. We know cavemen had a diet and that it would have had some effect on their flourishing, and it would have had a significant effect. But how does this factor compare to other factors bearing on their flourishing? Why was it their diet and not exercise, lack of predators, lack of competition with other tribes, etc., that resulted in whatever degree of flourishing they had? Perhaps it really was their diet, but it is an exceedingly difficult task of inference biological and historical inference to establish that.

    Here, I think, is the really crucial point: to gather evidence for whether cavemen were eating optimally, we have to first know whether cavemen were flourishing, and then identify its cause. Cavemen are very far away from us, historically. It is hard enough to know whether they were flourishing. I know there is some evidence for this, though it is based on a small number of surviving skeletons, and there is a serious question about how representative of the species these skeletons could possibly be, especially given that the stronger ones are more likely to have been buried well, etc. But what about determining the cause of their flourishing? This is harder still, because we can’t experiment with cave men to assess the relative weight of the diet factor vs. others. Everything we know about them is a product of inference.

    There is one way we could know more certainly what the effect of diet on caveman flourishing would have been: if we already have a general theory of diet that tells us precisely what force the factor of diet has under any given environmental circumstances. If we knew where to look to determine the circumstances of early man, this would tell us how to find evidence of the effects of his diet under those circumstances. But where are we going to get that general theory of diet? We would need to have the theory already to establish that cavemen were flourishing because of their diet. But then we could not use knowledge about cavemen as evidence for a general theory of diet.

    But of course it is precisely a theory of diet we are trying to establish.

    (The point is not that we need theories to establish knowledge of cause and effect. That is the opposite of a proper theory of induction, according to which we get inductive theories by first observing simple causal connections. But obviously we can’t observe anything about cavemen directly, since our entire knowledge of them is a product of inference.)

    We could get evidence for a general theory of diet by observing contemporary diets, though even here it is not direct observation because the body is a complicated mechanism with many variables affecting its flourishing. Still it is far easier for us to assess the causal role of our diet on *our* flourishing, since we are here now and can do experiments on ourselves (or on animals). But if we could get the theory that way, we would obviously have no need of historical knowledge to get it. On the contrary, we need contemporary knowledge to establish the theory, to establish any historical knowledge about the success or failure of past diets.

    So I think there is an important kind of hierarchy violation involved in the attempt to determine the best diet for us based on knowledge of the best diet for cavemen. We couldn’t know whether cavemen were eating the best diet unless we could establish a causal connection between their diet and their flourishing. Perhaps we can do that for them, but if we could, and if we knew where to look for evidence of the effect of their diet on their flourishing, it would probably be because we already had a theory of diet informed by our better knowledge of the effects of our eating on our flourishing. But we don’t have that theory–it’s exactly what we’re looking to establish.

    I don’t think that this means that thinking about diet and medicine in general in evolutionary terms is totally wrong. It is perhaps a useful heuristic device, an interesting thought experiment we can perform if we already have a lot of good evidence for a particular diet, which might summarize the results of that evidence. So the big question is whether we have that other evidence. I don’t think the evolutionary argument is itself is a form of evidence for the reasons given above, and so it and doesn’t lend independent support to a hypothesis about diet. That’s why I think contemporary studies are so important. To whatever extent we have them, they are our main form of evidence for the effectiveness of any diet. If they don’t tell us very much, then this limits the degree of certainty with which we could claim any knowledge of diet.


    There was, incidentally, also a long thread of discussion on this topic where the philosopher in question’s views were defended by NS:

    See especially this excerpt, the bulk of which went unanswered in the discussion thread:

    “But Aristotle knew better. He knew that any number of sophistical puzzles could be dissolved (and resulting rationalist solutions obviated) by distinguishing between the order of knowledge and the order of explanation. In his terms, this is the difference between “prior to us” and “prior by nature.” On his view, there is a distinction between knowing *that* something is the case, and knowing *why* something is the case. One can and often must know that something is true before one knows why it is true.

    To use Aristotle’s famous example. One can and must know that thunder is a noise in the clouds before one can know why thunder is noise in the clouds (because of the extinguishing of fire, he said). Or to use another of his examples: one can and must know that there is an eclipse before one can know why there is an eclipse (because the earth occludes the rays of the sun).

    How does one know that something is true before knowing what causes it to be true? In Aristotle’s examples, one just observes: one hears the thunder and one sees the eclipse. But there are ways of knowing beyond direct observation that involve inductive generalization and inference to the best explanation which do not yet involve explanation in terms of a master science. Evolution is the ultimate master science of biology, but there is plenty we can know in biology and in physiology before we know what explains it. I see no reason for thinking that one can’t know what is good to eat without knowing *why* it is good to eat in terms of a master science.

    And I see plenty of reasons for thinking why we *cannot* know why various things are good to eat in terms of biology without first acquiring a theory of nutrition based on physiological experiments performed in our own time. This is what happens in every other science. In order to know why the continents moved apart as they did, we first had to acquire theories of geology and electromagnetics and vulcanology, to understand how rocks and electromagnetic fields and volcanoes actually work, in order to know how they actually would have worked long ago to explain their present arrangement.

    Evolution is a theory for explaining *why* organisms function the way they do. It is not a theory for proving that they so function. We do not need to–and cannot hope to–prove that certain things are good for us by proving first why they are good for us. We don’t and can’t any more than we can hope to prove that the moon is in eclipse by first proving why it is.

    Or to use an example even closer to your position (because yours involves treating as a premise knowledge of distant eons: we cannot prove that the Earth is round by deducing it from knowledge of what caused the Earth to be round millions and millions of years ago. To give such an explanation in terms of the gravity of dust clouds, we would first need the theory of universal gravitation–which couldn’t have been formulated without first knowing that the Earth was round.”

    • christopolis

      thank you a 100 times over. I have had the same thoughts lingering in my mind but hadn’t done the work to clarify.Excellent.

    • Jennifer Snow

      Actually, it’s a pretty fair assumption that our caveman ancestors WERE eating the “best” diet because that’s how evolution works–the ones for whom it WAS the best diet survived and eventually produced us. The ones who weren’t adapted to eating what was available got sick and died and didn’t produce offspring. We are descended the people who were best-suited to eat *precisely* what was available to them, and since humans haven’t been around that long and have lengthy generations, we don’t change so substantially that it’s likely we are now particularly well-suited to eating things our ancestors did not eat. Each person must tailor this to themselves, but the foods that were available to our ancestors are a good starting place to look for compatibility, particularly when you see in the fossil/bone record when new foods were introduced due to agriculture, and people that were tall and healthy became short and riddled with disease.

      Evolution, in short, is one giant selection bias, which we can use to our advantage.

      I have some differences with some ancestral/paleo eaters over this, because they apply their concepts too universally for my taste, recommending absolute rules that may not apply. For instance, I have a radically different reaction to dairy than a large part of the world population, and I tend to have more issues when I omit it than when I eat it. I also have *radically* different food issues than the rest of my family–if you look at my body type and then look at my mom and brothers, you would probably not guess we were related. But this is also an issue of genetic expression–I was raised under radically different conditions than my mom and brothers which led to some pretty severe nutritional deficiencies, rampant insulinemia, an enormously depressed metabolism, etc. My early diet turned me on to extreme fat acquisition mode, and even eliminating as many problem factors as I can manage may not be sufficient to turn me into a trim person–the best I may be able to manage is to weigh 300 lbs. instead of 400 and to have moderate depression/anxiety rather than major depression/anxiety. I keep working at it, but I have to be realistic.

      So, what our ancestors ate is probably not the optimal diet for me. But it’s a huge, huge amount better than what I WAS eating before I learned about this stuff.

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