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I am a politically-progressive, ethically-herbivorous anthropoid pursuing a paleontology education in the Los Angeles Basin. I am largely nocturnal, have rarely been photographed, and cannot thrive in captivity.

15 December 2012

Food For Thought

I'm on winter break after a semester that was much busier than I anticipated. So, I'm gonna try to get some fresh material up over the next few weeks.

To start with, here's a thought I had the other day: a great deal of the cholesterol denialism found in the paleo and low-carb communities seems informed by a fundamental misunderstanding about the nature of adaptations. Ditto for a great deal of anatomical denialism among vegans, many of whom embrace myths that humans are obligate frugivores.

Consider the following two statements.
1) Homo sapiens are more adapted to meat-eating than other primates.
2) Meat-eating is unhealthy, at least in large amounts.

There's no necessary contradiction in those two statements, but I think a lot of paleo and low-carb folks think there is.

And, to be fair, so do a lot of vegans.

I've encountered many statements on paleo blogs to the effect that natural selection wouldn't have made us better at meat-eating if meat-eating was so dangerous to our long-term health. Or, put another, slightly different way, meat-eating can't be unhealthy because we are adapted to it.

In the vegan community, sentiment tends to run in the opposite direction, taking the form of the tiresome "humans are natural herbivores" meme: because meat-eating is unhealthy, humans therefore are not really adapted to it, and we're just fooling ourselves if we think otherwise.

Both forms of denialism rest on an assumption that adaptation carries with it an obligation (in this case, on obligation to eat other animals): paleos & low-carbers embrace fossil evidence and the implied obligation but deny the health evidence about cholesterol and saturated fat; while vegans embrace the health evidence while rejecting the implied obligation, which leads them to deny the fossil evidence.

So, here's the mistake they both make: being adapted to something doesn't necessarily make it "good" from the standpoint of individual health. There are many adaptations that come with a high price, and many others that have outlived their usefulness and have thus become burdens to be overcome rather than traits to be indulged.

A few examples from modern humans illustrate the point:

  • The unique human voice box, the anatomical source of our ability to use complex language, also makes it impossible for us to breathe and swallow at the same time... which means we're much more likely to choke to death on our food than other animals are. Language comes with the inherent risk of death by choking.
  • Chronic lower back pain is a direct consequence of our upright posture; hominoid primates have a transverse lumbar process that is serially homologous with the spinous process (rather than with the styloid process, as it is in other mammals), allowing us to assume more upright postures. But this mutation puts a lot of mechanical stress on the lower vertebrae, often leading to herniated discs. This is a risk few other mammals run, because the weight of their upper bodies is distributed along a longer axis.
  • Sickle cell anemia and the various forms of thalassemia are preserved in the human genome because they provide heterozygotes with greater resistance to malaria... despite the fact that heterozygotes suffer debilitating long-term health consequences from these adaptations, and recessive homozygotes die from them. For humans no longer living in malaria-prone areas of the world, these adaptations are now useless, and have become burdens rather than boons.

So, too, can it be for meat-eating. There's enough fossil evidence to plausibly argue that the genus Homo was given an edge in fitness by being better adapted to meat-eating than other primates. This allowed them to flourish on savannahs, under the selection pressures of the Pleistocene.

But this does not imply that meat-eating became healthier, from the point-of-view of degenerative disease. We still carry within us the mechanisms of atherosclerosis inherited from 22 million years of hominoid evolution, not to mention almost 200 million years of mammal evolution. We are, like nearly all extant organisms now living on this planet, a species of Rube Goldberg devices full of jury-rigged solutions that need only be good enough. If the traits of early Homo were good enough, there'd have been no need for the underlying biochemistry of cholesterol and atherosclerosis to be changed much, if at all.

Any advantage provided by adaptations to meat-eating would have been for the purpose of reproductive success, not "optimal health." That is, it would have provided early humans with a way of obtaining calories reliably enough, for long enough, to beat their rivals in the race to die with the most kids. Evolution, as I've pointed out before, is fundamentally about sex, not food or health. If being better at meat-eating allowed our ancestors to avoid starvation long enough to see their kids grow up, then it would have been preserved despite its atherosclerotic and other effects.

And thus, it's entirely possible that said adaptations are now burdens rather than boons, since we no longer face the selection pressures of life on the Pleistocene savannah. Something that helped us in the past can now be hurting us, and thus "eating like our ancestors" might be a terrible idea.

So, there's no need for denialism from either side of this paleo-vs.-vegan debate about diet. It turns out, they might both be right.

25 comments:

  1. I think this is the single most well - informed, even handed and intelligent statement I have ever seen on this topic. I must admit that I am unabashedly going to lift it whole and place it in my worldview. I never, ever comment on blogs, but I just couldn't let this pass without a heartfelt thank you. For a serving LEO having this discussion regularly with a very conservative and nutritionally paleo (from CrossFit, mostly) group of colleagues, this is pure gold. Enjoy your break, and thanks again.

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  3. Brilliant. Thanks a lot! Always good to add some new replies to the always same arguments. :)

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  4. So thoughtful. We need some intelligent thought on paleo from the vegan side, because I think there's good ideas in the paleo scene. Can you be the vegan Denise Minger? Write a book? The space is wide open.

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  5. Well written article. My compliments. The other thing about natural selection according to the late Roy Walford, gerontologist is that the adaptations are supportive of a species, not necessarily survival or longevity of an individual within that species. If a particular strategy ensured quick reproduction and survival to maturity of individuals within a species, that doesn't mean necessarily that older individuals within a community contribute to that species survival. If I remember correctly, Walford referred to it as the Parable of Ross's rats in his book the 120 year diet. Ross divided rats into two groups (not an experiment I ethically condone) and fed them two different levels of protein as a percentage of calories, something like 5 percent and 25 percent. The rats fed the 25 percent chow grew faster and reproduced more quickly but died earlier. It more readily ensured survival of the species since it provided earlier reproduction in the face of environmental stressors (disease, predation) but also gave the adults a shorter lifespan. The rats fed the 5 percent protein chow grew and matured later but lived longer. In short, natural selection is important but if we as individuals want to optimize our longevity, then natural selection and our evolution have to be seen in context. Paul

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  6. Nice post i really glad to read this informative post, thanks to share :)

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  7. Great chain of logic, enjoyable post. I do have questions though regarding the anatomical structure of humans being much more akin to herbivores than carnivores ( I am not denying our ability to successful digest and make us of animal sources). I recently watched a video by MIlton Mills http://www.youtube.com/watch?v=sH-hs2v-UjI.

    I am curious your response to it. Can you link to other posts were you have discussed this already? Or, another resource that you like that shows counter evidence to what he presents. I definitely don't like his tone and zealousness, but he seemed to make some very valid points.

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    1. Hi Michael,

      Sorry it took me a while to get this. Blame the holidays.

      I'd level the same criticism at Mills that I lay on paleo folks who use the same tactic to make the reverse case: namely, that he doesn't distinguish between derived and primitive traits, between adaptation and exaptation, doesn't account for co-optation or convergent evolution, and a whole host of other important and relevant details.

      It's argumentation by laundry list. I don't really have any previous posts dealing specifically with this topic, but I think you just inspired me to write one. :)

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  8. Hey, any time that you think you've got a tough lot because you've (basically) got to deal with a lot of "scientistic" arguments in favor of meat-eating...

    ...consider what it would be like to be a member of a religion that forbids killing mosquitoes...

    ...and yet offers an array of lame excuses to justify eating meat on a daily basis.

    http://a-bas-le-ciel.blogspot.ca/2012/06/vegetarianism-and-theravada-orthodoxy.html

    Sadly, almost nobody thinks scientifically about the posits of science itself; and, thus, "scientism" becomes as dogmatic as any other religion. Of course, almost nobody thinks scientifically about religion, either. Things are rough all over.

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  9. Thanks for this post! Every time you post I am so glad, once for your thoughts and information and also just for feeling less alone as a vegan sceptic.

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  10. What about humans being somewhat closer to an unspecialized frugivore?

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    1. Carlos,

      "unspecialized frugivore" = omnivore.

      These aren't mutually exclusive categories.

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  11. Thanks for the brilliant post. I will be linking people here in the future.

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  12. Hmmm not having sex and not eating meat ... even if you don't live longer at least it will feel a lot longer.

    Consider the following two statements.
    1) Homo sapiens are more adapted to meat-eating than other primates. ( we're also WAAAY better at hunting , fishing , cooking , curing.) And even better than some carnivores at utilizing the whole animal.
    2) Meat-eating is unhealthy, at least in large amounts.Mute point (too much water can be deadly)

    It's just as likely we acquired a mutation that required us to eat meat.

    I prefer the term animal-eater, meat-eater implies that I only eat muscle, when I actually eat stomachs , intestines, tendons,various glands, livers and hearts too.

    The Shrew ancestor to us all.

    All elephant shrews eat mainly invertebrates, such as insects, spiders, centipedes, millipedes, and earthworms. An elephant shrew uses its nose to find prey and uses its tongue to flick small food into its mouth, much like an anteater. Eating large prey can pose somewhat of a challenge for the elephant shrew. For example, a giant elephant shrew struggling with an earthworm must first pin its prey to the ground with a forefoot. Then, turning its head to one side, it chews pieces off with its cheek teeth, much like a dog chewing a bone. This is a sloppy process, and many small pieces of worm drop to the ground; these are simply flicked up with the tongue. Some elephant shrews also feed on small amounts of plant matter when available, especially new leaves, seeds, and small fruits.[7]

    I like the shrew diet.

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    1. It's just as likely we acquired a mutation that required us to eat meat.

      Well, no, Alex, it really isn't. Any such mutation would have to eliminate or otherwise cancel out 22 million years of hominoid inheritance. And that's just not how evolution works.

      Shrews are not the ancestors of us all. The ancestor of us all no longer exists.

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    2. Not quite sure where Alex gets the "not having sex" part of the equation from. Maybe over-active imagination?

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  13. Don't tell me how evolution works neither you or I know, there are too many variables , we have educated guess, and fun speculation.

    They don't call it a "mutation" for nothing:

    " Human cells cannot perform the crucial last step of vitamin C biosynthesis, the conversion of l-gulono-g-lactone into ascorbic acid, which is catalysed by the enzyme gulonolactone oxidase. As a follow-up to Lehninger's work several years later, Nishikimi and co-workers observed that the gene that codes for gulonolactone oxidase is actually present in humans, but is not active due to the accumulation of several mutations that turned it into a non-functional pseudogene (Nishikimi & Yagi 1991)."

    Buy ancestor to us all I meant all mammals . A modern shrew ,no. Something(insectivorous) like a shrew ,according to Richard Dawkins, yes.

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    1. Don't tell me how evolution works neither you or I know, there are too many variables , we have educated guess, and fun speculation.

      Nope. Dead wrong. We know most of the laws and rules of evolution pretty well. You're simply wrong, it's not an opinion question, or speculation.

      Try taking a college-level course in evolutionary biology.

      Your citation of the De Tullio article only compounds your fail. The lack of vitamin C biosynthesis is not a fundamental change to hominoid inheritance; on the contrary, it's one of the defining features of the clade, and one that pretty much requires our ancestors to eat fruit. But if you look at the chemical signalling pathway, you'll see that all the ancient infrastructure is still there. It didn't go anywhere, which is what allows us to synthesize our vitamin C needs through diet. The biochemistry gets us most of the way there, doing the same job it does in all other animals, and then gets a little boost from our diet. In an environment where abundant exogenous vitamin C is available, there's no selection pressure to maintain the endogenous capacity, and it atrophies... but only at the end point, because the rest of the pathway is still needed.

      Natural selection retains most non-deleterious changes over evolutionary time. It's a huge Rube Goldberg affair. You are built on a hominoid template going back 22 million years, and are stuck with all the traits that implies. An improved ability to digest animals would simply be a modification of a trait that all hominoids already possessed, and thus is neither a fundamental change to the template,nor a requirement to eat meat.

      You only have requirements for specific nutrients, not specific nutrient sources. Your body doesn't care where the nutrients come from, so long as it gets them.

      If you'd actually read Dawkins, you'd understand this better.

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    2. Carnists... Holding on for dear life on any little thread they can muster.

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    3. Excellent ,perhaps you can tell me how many years it takes to lose the vitamin C synthesis ability . (vitamin C is in pretty much all plants not just fruit.)

      I don't doubt evolution , we know it happens.

      I doubt your wacky interpretation of it.

      Vitamin C is a perfect example .

      Let's replace vitamin C with (yet unknown essential nutrient from animals )

      " In an environment where abundant exogenous [YUE nutrient from animals] is available, there's no selection pressure to maintain the endogenous capacity, and it atrophies... but only at the end point, because the rest of the pathway is still needed."

      2 million years of ever increasing animal consumption had no effect?




      Okay. I'm done,peace be with you, Enjoy your religion (Jainism) .

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