I think it’s worth noting that, subsequent to thousands of years of evolution and selection, local human populations are differently suited to different diets. The most obvious (and frequently cited) example is lactose intolerance among most of the world’s people, specifically those who have not spent the past 8000 years raising (and milking) cows and sheep.
But other examples are more apropos to this column. For instance, many indigenous peoples of Papua New Guinea subsist mainly (if not entirely) on the starch of the sago palm tree; they would probably find more health problems with eating red meat than, say, some Inuit tribes who eat nothing but deer meat from cradle to grave. The fact that Chinese people do better with a largely vegetarian diet is unsurprising, given that rice and soybeans have been staple products there for thousands of years. Run the same study against, for instance, the San people of southern Africa whose desert dwellings make vegetables few and far between, and you’d find very different results, I’d bet.
I think it would probably behoove the vegetarians in question to remember that humans evolved in very different environments and, as such, have different dietary dispositions. What’s good for the goose, in this case, may not be good for the gander.
Thank you for a good post, including a link to the column and some straightforward discussion.
However, your argument is not completely accurate. There is no real evidence anywhere that local populations are differently suited to different diets. All evidence points to just the opposite: that all humans can adapt to any diet as eaten anywhere.
Your confusion is taking individual foods for diet. It is certainly true that up until a few thousand years ago virtually everyone in the world was lactose intolerant as an adult. A mutation that never stopped the manufacture of lactase turned out to have selection advantage as dairying spread. However, it’s still true that most people in most cultures can have some dairy in their diet without symptoms. Cultures developed the use of butter and aged cheeses as well as fermented foods like yogurt and kumiss, all of which are low in lactose. Even in Asia, where the original gene allele for lactase deficiency is widespread, some dairy has historically been part of the overall diet and dairy products are increasingly found in modern foods and stores.
In the same way, allergic reactions and digestive diseases may prevent some people from eating some foods without symptoms, but that doesn’t mean that any populations are not suited to eating these foods. It’s the same for cultural prohibitions for eating pork. A believing Jew or Muslim may get ill if forced to eat pork, but that’s a psychological problem not a gastrointestinal difference.
Explorers have proven for hundreds of years that people can adapt to local foods no matter what they are or where they go. There are even solid experiments in which people ate a literally all-meat diet for a year without any deterioration. For that matter, immigrants change their diet as part of their move to a new country and culture all the time and it’s too common an event to comment upon.
Local preferences developed over a short period of anthropological time have nothing to do with how human anatomy functions. Humans are omnivores. They can and have eaten everything potentially edible on the planet. While there are certain individual foods that are bad for certain individuals, anybody on the planet can adapt to a different overall diet.
Point taken: “dairy” does not necessarily mean “milk,” so a population that is lactose intolerant is not necessarily dairy-poor.
But it still seems to me – although I’ve no cites to back this up – that if you or I tried to consist on a diet entirely of sago palm starch or reindeer meat, we’d suffer from malnutrition pretty quickly. It sounds – correct if I’m wrong – like you’re claiming that we wouldn’t need to go through centuries of evolution to adapt to this diet, but rather put up with a few weeks or months of the trots; in other words, regional diets being suited to regional populations is a product of nurture, not nature.
I do recall hearing somewhere – again, I don’t have any cites – that people of Asian ancestry in the U.S. live longer, healthier lives than other Americans as long as they eat their traditional foods; once they adopt American eating habits (whatever those are), though, they live shorter, less healthy lives than other Americans. This suggests, to me, that there is a genetic component that has at least some impact on ideal diet. This is, unfortunately, all null and void if I can’t point you to the article; anyone else out there in SDMBland recall the study of which I speak?
Yes, exactly. Assuming there’s enough nutrients in the sago palm starch, your body would adapt; not evolve. All humans are pretty much the same in this regard. There’s very little difference between the PNG folks and us in the digestive track. If you took a PNG child and raised them eating another diet they wouldn’t have any problems either.
Suppose you took Americans without Asian ancestory and fed them on a traditional Asian diet, which is presumably healthier. Don’t you suppose they would live longer as well? I’m not clear where genetics enters into this.
One non-dietary counterpoint: most humans will adapt when going from sea level to high altitude. It doesn’t matter where you were born and raised, we all have that ability. Even people raised at high altitude will have altitude problems if they spend a long period of time at sea level; they lose their adaption. But some populations (Sherpas for example) have physiological advantages to spend time at high altitude. People without that ancestory are at a disadvantage. It’s not something that you can adapt to.
Genetics enter into it because Asian Americans who ate an American diet didn’t live as long as Americans without Asian ancestry who ate an American diet. I agree that the traditional Asian diet is better than the modern American diet; that’s not what the study was testing.
That’s an interesting bit about the sherpas. It seems to me, to do a brief thought experiment, that if thousands of years of living at high altitudes would confer physiological advantages at altitude, it’s strange to think that thousands of years of eating a specific diet would not. We see similar small-scale differentiations in local human populations – the already mentioned altitude, skin color adaptations to the degree and intensity of sun, body proportion adaptations to temperature, etc. Why wouldn’t there be small differences between the digestive tracts of an Inuit – whose ancestors have eaten mainly meat for the past 5000 years – and an Iranian, whose ancestors have been eating cereals for longer than practically anyone else on the planet?
I didn’t know that some non-human primates ate meat until a year or so ago. Be The Creature, I think it was, had some footage of chimpanzees or monkeys hunting monkeys and eating them.
I’d have to examine the study protocols carefully before I commented on it. As a general rule, I have problems with the majority of longitudinal epidemiological studies. They look at too small a population for too short a time, and do too poor a job of controlling other variables.
The main objection to this line of reasoning is that most cultures already eat a variety of types of food. All cultures already eat a mixture of proteins, fats, and carbohydrates rather than a single food source. Whether the source of the carbohydrates is from cereals or other types of plants is not a big deal: the enzymes will work equally well on each. Whether the source of the protein is plant or animal is similarly not an issue. As long as a complete set of amino acids are regularly ingested, the body doesn’t care what whole proteins are being broken down to achieve that.
So unlike the other factors you name, there is no selective advantage for bodies to specialize in certain food enzymes. In fact, this would undoubtedly be a disadvantage because food sources change markedly in very short periods of time as climates change, human populations gain expertise in agriculture, plants and animals migrate, and tribes and individuals simply move around.
Again, lactose tolerance is an interesting and unusual exception. It is the rare mutation - neutral in essence for most of humanity’s existence - that suddenly became an advantage because of cultural factors. There’s little reason to think that several such mutations would suddenly become culturally advantageous. That’s too much to expect.
Humans have a tremendous advantage being omnivores who can eat everything and anything from the start. We don’t need anything else besides that in evolutionary terms. We already have the ability to adapt to any type of food naturally on earth in no time at all.
It would actually be nice if your mistaken idea was true: then we could adapt to having all these empty calories from sugars and fats in our modern diet, and not all become obese and otherwise unhealthy from them. But we’re stuck with systems that are 99.99% the same as they were 200,000 years ago or whenever H. sapiens is now thought to have started. They’re great systems and they functioned exceptionally well all this time. We just have to hope that our current bad habits don’t kill us off, because there is no evolutionary way we can adapt to them.
That seems pretty questionable. Under what circumstances is a system immune, as it were, to evolution? Why wouldn’t natural selection reward those individuals who were minutely better suited to the modern American diet? Admittedly, most of the most visible problems with said diet come after the age of reproduction, but good health is certainly rewarded during the mating process. How could the digestive tract become immune to evolution?
Evolution is always a slow process, especially for organisms with a 15-20 year generational span, and it’s gotten even slower, since we’ve started using tools that enable almost all humans to have as many kids as they want. Diets change over much shorter timescales than evolution can handle. In principle, evolution is acting on our digestive system and everything about us, but by the time that people start eating differently, evolution has made such a small change to our innards that it’s completely negligible.
If you are talking about the Khoi san (bushmen”) then traditionally their diet consisted of around 70% plant matter by bulk and around 50% by calorie intake. In no sense were vegetables few and far between. They ate far more vegetable matter and a far greater diversity of vegetables than modern Americans.
No human lives entirely on one plant food. It’s impossible because they are nutritionally incomplete. There are people who live largely on one type of plant food be that rice or potatoes or sago but they supplement the diet with other material. In the case of New Guineans they also eat insects, fish and pork fro protein. Nonetheless protein deficiency amongst these people is almost universal and they would and should eat more meat if possible.
One example that might better fit your argument is the necessity of some Eskimo groups to eat seafood. After millenia of a high seafood diet they have lost the ability to synthesise several vital oils and must obtain them from their diet. A diet deficient in seafood results in brain and nerve damage. This is on some ways analogous to the evolution of lactose tolerance, where the simple fact that a gene was no longer required led to it becoming widespread.
It seems to me a good argument against vegetarianism by nature has been omitted:
We have two eyes set carnivore-wise on the front of our head. This is to enable us to judge the distance to our prey.
If we were strictly evolved to be vegetarians, we wouldn’t need hunter’s eyes. After all, it’s not like the plant you wanted to munch on is going to up and run away from you.
I saw a similar program 10-12 years ago. Chimpanzees hunting a monkey of another species (can’t recall which). The hunting technique was ingenious, though mostly the product of instinct. I think it was a “team” of five or seven chimps. The biggest of the group just walked in a straight line through the jungle, making as much noise as he could to scare up potential prey. On either side of him, other chimps moved quietly and swiftly on the ground and in the trees. The job of these “outriders” was to spot any potential prey running from the big, noisy chimp, and quickly move to get ahead of it in a surrounding maneuver. When they finally caught up with the unfortunate monkey, they proceeded to rip it to pieces and eat its eyeballs (delicacy!) The chimps seemed to find it quite natural to devour the monkey.
Did you see the news footage of the poor people being rescued in New Orleans after Hurricane Katrina? We saw great examples of those who are the primary, major consumers of the “American diet”, and it’s well-known that the poor tend to breed very rapidly, healthy and attractive or not, producing many more avid consumers of the “American diet”. I know more poor people with six kids (“Yeah, gimme eight double cheeseburgers, eight large fries, and eight Cokes!”) than rich people with six kids.
(I’m not dissing the poor. I’m poor myself. And I choose not to breed.)
Evolutionary “progress” is dependent upon a fairly consistant environmental impetus that effects some result on reproductive fitness, or more to the point, the ability to successfully propogate genes; that if it grows consistantly colder, a species will change to maintain effective thermoregulation, for instance. In the case of diet, the recent high-carb/low fiber, refined sugar diet with excess calories year round is aberation in human evolution; even (as has already been pointed out) groups who subsist on a largely simple starch-based diet require supplementary proteins and fats, and no amount of evolution is going to make up for the dietary need for essesntial proteins that we can’t synthesize. Despite the negative health impact of the typical American diet, this has little impact on the ability of Americans to reproduce; even persons with poor dietary habits are sufficiently healthy to have children (and undoubtedly pass on their own bad habits). Whatever the evolutionary effect of that may be it’s unlikely to be very quick or directed.
I see that we have a Larry Niven fan in company. Unfortunately, Niven’s understanding of evolutionary theory is nearly as simplistic and reductionist as his skill at characterization. Having eyes foreward means nothing in particular with regard to diet; there are plenty of predators with side-mounted eyes, and many vegetarian primate species with eyes forward. Side-mount eyes are certainly useful to herd animals who are ever-wary of predators, but binocular vision isn’t particularly useful for gauging relative distances beyond a few feet. (If you don’t believe me, close one eye and try gauging distances at or beyond arm’s length–you’ll have very little difficulty.) Forward-located eyes, at least in primates, probably have far more to do with the nature of socialization and use of facial “gestures”, as well as manipulative abilty, than eating habits.
The real–and only necessary–test of the evolved dietary standards is what material the digestive tract is developed to process. In bovines, for instance, the long tract and multiple stomachs are designed to break down cellulose. In cats, the short intestinal length indicates the need for a high protein diet. In humans, like other omnivores (pigs, bears) the intermediate length of the digestive system, need for vitamins typically found in fruits, need for fiber, and limited tolerance for high protein diets indicates an omnivorous diet. QED.
Owing to the relatively short timespan of modern human divergence in diet, there is little reason to believe that there are significant differences (aside from minor alterations such as lactose tolerance or dietary pressures in small, isolated, highly inbred populations) between populations in terms of nutritional requirements.
As well as looking at the digestive system, we could compare our teeth to other mammals.
Look at a cat or weasel skull, and what do you see? Long thin shearing molars, tiny incisors. Look at a sheep, what do you see? Grinding molars that grow throughout life, with layers of different material that keep the grinding surfaces sharp by differential wear. Look at a human skull, what you you see? Flat crushing molars, similar to the molars of a racoon or a pig or other omnivores and generalist non-grazers.
Of course, humans don’t NEED to eat meat, with a little care you can be perfectly healthy on a no-animal-protein diet.
You can also eat a very meat heavy diet, although scurvy is going to be a real problem, since humans and other primates have lost the ability to synthesize vitamin C. However, raw meat has a little vitamin C, so eating your meat raw will stave off scurvy, and if you can get a few summer berries and greens and preserve them in oil like Inuit you’ll survive. But you’d probably do better with more fruit and vegetables in your diet, you have to be a lot more careful with a nearly all meat diet than you do with an all plant diet.
Well, any vegetarian who stopped to think that chimpanzees eat termites, and that’s been widely known forever, would realize our closest relatives are omnivores. Gorillas are the only primates I know that are vegetarian.
I was under the impression that the leap in the evolution of brain size from small to large was in part due to the eating of meat. However, this could be circumstantial since the ability to obtain meat must have indicated the state of the brain at that point–which is to say it must have been advanced enough to make a weapon and wield it to hunt sucessfully. After reading about how the chimps hunted, I guess this behavior is not that “advanced.” But I’d have to say that if early humans were vegetarian (with or without insects), then started to eat meat, and then developed as omnivores, then this would have lent them an evolutionary advantage. As a few have already pointed out, this would have given humans an adaptable diet where if they were restricted to beef or restricted to the starch from palm trees, they would still be able to survive. Maybe this is the lasting contribution of ancestors who began adding meat to their diet–if not for brain size, then for quick adaptation to their changing surroundings.
Except that it is very likely that humans never had an ancestor that was a strict vegetarian, we’ve probably been omnivores back to the first apes, and the first primates were probably mostly insectivores.
So it’s probably not accurate that our early ancestors were vegetarians who got sick of the carrots and fruit and decided to add some raw meat. We were always omnivorous. The hypothesis that there’s a feedback loop between increased meat, increased brain size, and more efficient hunting, and back to increased meat seems plausible.
But I don’t think we’re much more adapted for eating meat than chimpanzees. We do have much smaller incisors, which chimps use to prepare plant food–biting off and discarding low food value plant parts that are woody and tough to get to the higher-value parts. But humans have probably been using hands plus tools for the last couple million years for those types of tasks. Gorillas might acurately be described as vegetarian, but chimps certainly aren’t, and neither are most other primates.