Social Evolution Forum
FIND sef:
The Dark Side of Cultural Evolution

Cultural evolution is what created the – in many ways – wonderful societies that we live in. It created the potential to free our lives from hunger and early death, and made possible the pursuit of science and art. But cultural evolution also has a dark side, in fact, many ‘dark sides.’

Clearly domestication of plants and animals is what made our civilization possible. All sufficiently complex societies are possible only on the basis of agriculture. But we have paid, and continue paying a huge price for this advance of human knowledge and technology. This idea was brought home to me as a result of several conversations I had with Michael Rose during the Consilience Conference at St. Louis, which I talked about in my previous blog. Michael is an evolutionary biologist at the university of California at Irvine, who studies aging from the evolutionary perspective. I actually read his book Evolutionary Biology of Aging some twenty years ago, but never met him until two weeks ago.

One way people talk about the price of civilization is in terms of evolutionary mismatch (which is one of the focus areas at the Evolution Institute). The idea is that our bodies and minds evolved during the Pleistocene, when we lived in small groups of hunter-gatherers. Now we live in a dramatically different environment, and that causes all kinds of problems. The psychological aspect of the problem was recently discussed by Robin Dunbar and commentators on his Focus Article. The physiological problems include rampant obesity, heart disease, and diabetes.

There is currently no consensus on the role of changing diet and other aspects of lifestyle, most notably exercise, in causing modern-day health problems. Some people argue that our Plestocene bodies are not adapted to high-calorie diets and sedentary life-styles of today. On the other hand, agriculture was invented roughly 10,000 years ago. 400 generations is not an insignificant length of time for evolution to do its thing. Some anthropologists (including another participant of the Consilience conference, Henry Harpending) argue that humans evolved very intensively during this period. One famous example is the evolution of lactose tolerance, that is, ability to digest milk.

Michael Rose develops a more subtle and sophisticated argument, which is explained at length in his 55 theses – a New Context for Health. There is a sophisticated mathematical model underlying his argument, but the basic logic of it is actually quite simple.

We think of people having ‘traits,’ but actually we change quite dramatically as we age. The key ‘trick’ is to realize that people have a suite of traits, and they can be quite different, depending on what stage in life we are talking about. As an extreme example, consider reproductive ability, something of great interest to evolution. Humans do not reproduce until they reach a fairly advanced age of maturation (puberty). Young adults are not very good mothers or fathers, but they improve with age during their twenties. After that reproductive ability declines and eventually disappears. So reproductive ability is actually a trait that varies quite a lot with age.

Another example is hair color. One man can have red hair and another blond hair. However, this will be true only while they are relatively young. Older men become grey, and many become bald. So by the time our two men turned 60, they may have the same hair color (grey), or no hair at all (bald). By the way, it is likely that the reason is not simple ‘degradation,’ reduced function due to aging, but that greyness and baldness evolved to signal maturity and wisdom. To really describe the phenotype of an individual we need to specify at what age it is expressed.

Ability to digest certain foods can also be age-dependent. I have already mentioned the ability to digest lactose, the sugar present in milk. Before we domesticated animals such as cows and sheep, only very young humans had this ability. Natural selection turned this ability off in adults because they never needed it (and it would be wasteful to continue producing the enzyme lactase that aids in the digestion of milk sugar).

Now clearly traits expressed at different ages are not completely independent of each other. An ability to digest milk sugar as an adult depends on the presence of an enzyme that evolved in order for babies to digest their mother’s milk. So traits at different ages can be correlated, either positively, or negatively. An example of negative correlation is the reproductive ability – in many animals, putting a lot of effort in reproducing early reduces the reproductive ability later in life. So the sophisticated mathematical framework for dealing with age-dependent traits has to take into account all kinds of possible correlations, both between the same trait at different ages and between different traits. For example, most individuals have dark eye and dark hair color, or light eye and light hair color, with dark/light and light/dark combinations a relative rarity.

We can now get to the crux of the matter. Because abilities to do something at the age of 10, 30, 50, etc. are separate (even if correlated) traits, they evolve relatively independently of each other. When grains became a large part of the diet, the ability of children to digest them (and detoxify the chemical compounds plants put into seeds to protect them against predators such as us) became critical. If you don’t have genes to help you deal with this new diet, you don’t survive to adulthood and don’t leave descendants. In other words, evolution worked very hard to adapt the young to the new diet. On the other hand, the intensity of selection on the old (e.g., 55 years old) was much less – in large part, because most people did not live to the age of 55 until very recently. Additionally, once an animal gets past its reproductive age, the evolution largely ceases to have an effect (in humans, presence of older individuals was somewhat important for the survival of their genes in their children and grandchildren, so evolution did not entirely cease, but was greatly slowed down).

What this means is that evolution caused rapid proliferation of genes that enabled children and young adults to easily digest novel foods and detoxify whatever harmful substances were in them. Genes and gene combinations that did the same for older people also increased, but at a much, much slower rate. This may sound puzzling – if we have the detoxifying genes that work for young adults, why shouldn’t they work for older adults? The reason is that one gene-one action model is wrong; it’s not how our bodies work. Most functions are regulated not by a single gene, but by whole networks of them. As we age, some genes come on, and others go off, and the network changes, often in very subtle and nonlinear ways. That’s why we need the ‘trick’ with which I started, to consider functions at different ages as separate traits. During the last 10,000 years evolution worked very hard to optimize the gene network operating during earlier ages to deal with novel foods. But the gene network during later ages was under much less selection to become optimized in this way.

The striking conclusion from this argument is that older people, even those coming from populations that have practiced agriculture for millennia, may suffer adverse health effects from the agricultural diet, despite having no problems when they were younger. The immediate corollary is that one thing they can do to improve their health is to shift to something known as the ‘Paleolithic diet,’ or paleo diet, for short. In the simplest form, this means eliminating from your diet any cereals (wheat, rice, etc), legumes such as beans and peas, and any dairy products (e.g., cheese). It is striking that this is almost precisely the opposite of the popular Mediterranean diet, which emphasizes wheat products (bread, pasta), cheese, and legumes (as in the Italian bean soup, in pasta fagioli, and in hummus).

We are now getting to something I have a personal (rather than a scientific) interest in. I am about to turn 55, and although I am generally in good health, various worrying indicators – cholesterol, sugar – have been inexorably inching up. A couple of years ago I read Ray Kurzweil Fantastic Voyage, but I was unpersuaded by his prescriptions to better health and longevity. Kurzweil’s prescription is, at basis, a calorie-restricted diet. Like the great majority of human beings, I find it extremely difficult to starve myself. More generally, his approach to human health and longevity is that of an engineer – you turn that dial down, another one up, and get the result you want (according to his book, he spends one day a week connected to a machine that removes bad things from his blood and adds good things). I am very doubtful that such an approach will work on an evolved system with multiple nonlinear feedbacks, which is the human body. So changing one variable (e.g., reducing the cholesterol level in the blood) may have unintended – and usually negative – consequences elsewhere (perhaps increasing the risk of cancer).

To conclude, the paleo diet is the first diet, of the ones I heard of, that has a sound evolutionary basis going for it. This was a deciding factor in persuading me to try it out, which I did, starting about two weeks ago. It apparently takes about six months to see its full effects, so stay tuned for progress reports.

11 Comments

Join the discussion

11 Comments

  1. tmtyler says:

    Mild calorie-restriction is still helpful. The ancestral diet probably sucked, and isn’t to be emulated in detail by modern folk – IMHO.

    • Peter Turchin says:

      I found that simply eliminating all cereals from the diet has resulted in a ‘crypto-calorie restriction.’ No bread, not pasta, no rice… substituting cauliflowers, squash, asparagus, etc works well in terms of resulting in filling meals, but clearly such meals have a much lower energy content.

  2. The problem with the modern diet is not that it differs much from the so called paleolithic diet (it does not), but that a large portion of it is processed by the criminally incompetent processed food industry. It is not a good idea to select huge amounts of seeds to eat, but such a habit fades into almost insignificance if the seeds first have the germ and bran removed by the millers. As much as 75% of the potassium is lost from a food that is already marginal in potassium for instance. The sugar industry is even worse. That industry removes 100% of ALL essential nutrients. There is nothing wrong with milk as a food, except that it is devoid of copper. So small amounts of milk would not be harmful to those able to digest lactose as long as copper was being acquired elsewhere (see link to charles_w.tripod.com ) . On top of that, processors add numerous poisons to food such as aluminum, fluoride (probably responsible for Alzheimer’s disease), aspartame, capsaicin from chili (which I suspect is causing type 1 diabetes, see link to charles_w.tripod.com ), and etc. On top of that nutrients are added and subtracted in wildly varying amounts. This can lead to imbalances such as the dangerous imbalance between potassium and thiamin as resulting in heart disease (see link to charles_w.tripod.com ). So paleolithic is not the important concept. The important concept is processing as practiced as opposed to correct processing.

  3. liveoaklinda says:

    wow – love this (kind-of ‘duh’) idea that our digestion ability changes with age. My current goal is to avoid potatoes, refined wheat & refined sugars (with the major exception of wine – that surely must have been part of the paleo-diet, no?).

    • Peter Turchin says:

      Our monkey ancestors have been eating fruits for millions of years. Ripe fruits have a tendency to ferment, so it is reasonable to supose that our ancestors have been eating fermented fruit also for millions of years. We have a pretty elaborate biochemical machinery for digesting alcohol. But distilled spirits (alcohol in high concentrations) are surely novel.

      According to Michael Rose, monkeys actually love to get a high from fermented fruits.

      • I doubt if those monkeys ate spoiled fruit if they could find unspoiled. But in any case, I doubt even more that they were stupid enough to add sulfites to the fruits. It will take more than until October to know if anything is working. Even a life time will not be enough if some other unrelated health problem or advantage intervenes, say being shot by a jealous husband for instance or a natural poison or advantageous substance in one of the foods you eat routinely. I suspect you are on the right track, though. I hope so.

  4. Peter Turchin says:

    @Charles Weber: No argument that the industrial revolution resulted in the introduction of a whole suite of compounds into our diets, many of which could well be slow-acting poisons with grave consequences for our health. It is a plausible hypothesis that the epidemic of obesity among the young people is, to a large degree, the result of this dietary change. However, this does not negate the argument I was discussing that deals with lesser degree of adaptedness among the older people to agricultural (pre-industrial) foods.

    And in any case, following the version of the paleo diet that I adopted (no cereals, no legumes, not dairy) actually forced me to completely eliminate processed foods. Not that I had been eating a lot of them before, but now I don’t eat them at all.

    In the final analysis, the great thing about adopting any diet is that you experimentally find out whether it works for you, or not. After two weeks, it is already clear to me that I can go on this diet indefinitely. Now the question is whether it will have the supposed health effects, or no, which I will know by October. So I couldn’t care less whether randomized trials support it or not. I only want to know whether it works for me.

  5. Very interesting and clear discussion of something I’ve been exploring in my work for several years. I do believe we are, or could/should be evolving, as a species, towards being able to efficiently utilize whole grains and beans and raw milk dairy as alternate proteins to meat. Maybe if we’d just stuck with these novel foods in their natural sate–sans all the processing, refining, etc, that seems to have captured our culinary/industrial imaginations–we’d be a little better at it by now, 10,000 years in. Einstein, I believe, said that the survival of the human species depends on our evolving to a vegetarian diet. I personally don’t like eating animals for ethical and spiritual reasons, and the social-environmental argument against large-scale meat consumption is also strong. On the other hand, beans are not at the top of my personal high-digestibility food list, and according to your post here (with which I agree), things won’t be improving in that department! What’s an aging, post-neolithic veggie to do?! Hello eggs, raw goat cheese, sprouted seeds, nuts… and some tofu/tempeh/miso here and there…

  6. Peter Turchin says:

    Diana, populations evolve, but the cost is all those ‘unfit’ individuals, who get selected away. So if you are one of those ‘unfit’, what do you do?

  7. Good question, and I wonder myself… Fortunately, evolution is a slow boat to China, and we, the ‘unfit’, aren’t selected away in a puff of smoke! Maybe we can try to shift the phenotype by feeding our offspring a little differently than ourselves, in a conscious effort to adapt future generations towards a more globally sustainable diet? Sensibly, of course. For instance, I’ve seen research suggesting that celiac disease developed as an adaptive advantage, the theory being that when wheat first entered human diets, children who could expel gluten toxins through intestinal inflammation-induced diarrhea had a better chance of surviving to reproductive age. But not very comfortably! Hence, not necessary to force wheat on our gluten-sensitive kids! But there are kinder, gentler grains…and traditional ways of preparing them to reduce their anti-nutrient load (soaking, etc).

  8. Ross says:

    ArtDevanyOnline has a great, technical slideshow on this including broad background, biological background and practical pointers. He doesn’t consider himself “paleo”, but is a leader in the field of long-time practitioners.

    Mark Sisson over at MarksDailyApple has a ton of study references, actual cases, and pointers as well.

    Can’t wait to hear about ongoing results, and wish you the very best of luck! (Might want to get some pre-plunge baseline tests done, just for fun….)