Grain, disease, and innovation

By Razib Khan | June 18, 2011 2:04 am

I just finished reading a review of the literature since 1984 on the bioarchaeology of the transition to agriculture. Stature and robusticity during the agricultural transition: Evidence from the bioarchaeological record:

The population explosion that followed the Neolithic revolution was initially explained by improved health experiences for agriculturalists. However, empirical studies of societies shifting subsistence from foraging to primary food production have found evidence for deteriorating health from an increase in infectious and dental disease and a rise in nutritional deficiencies. In Paleopathology at the Origins of Agriculture (Cohen and Armelagos, 1984), this trend towards declining health was observed for 19 of 21 societies undergoing the agricultural transformation. The counterintuitive increase in nutritional diseases resulted from seasonal hunger, reliance on single crops deficient in essential nutrients, crop blights, social inequalities, and trade. In this study, we examined the evidence of stature reduction in studies since 1984 to evaluate if the trend towards decreased health after agricultural transitions remains. The trend towards a decrease in adult height and a general reduction of overall health during times of subsistence change remains valid, with the majority of studies finding stature to decline as the reliance on agriculture increased. The impact of agriculture, accompanied by increasing population density and a rise in infectious disease, was observed to decrease stature in populations from across the entire globe and regardless of the temporal period during which agriculture was adopted, including Europe, Africa, the Middle East, Asia, South America, and North America.

The abstract makes the conclusion more cut & dried than it is. It’s the result of aggregating their literature review and arriving at a net conclusion. Yes, on the balance agriculture did result in the deterioration of health. The old truism that farmers are a small and ill lot in comparison to hunter-gatherers seem to be correct in the generality. But the literature review also makes it clear that when it comes to something like stature there are often periodic reversals of the trend toward decrease in size. There may be spottiness of the record, and sampling error, but I began to wonder if we might not be seeing evidence of evolution & innovation in action!

Consider the checkered history of the potato in Ireland. In the 18th century the Irish shifted toward the potato faster than most other European peoples, and so entered into a phase of massive population expansion. On a per unit basis the potato was nutritional gold. Unfortunately we all know that the blight of the 19th century triggered a series of social and demographic catastrophes.


But, the insight here is that we may have to think of the “transition to agriculture” as a more complex affair. My conceptualization is most easily illustrated by a chart:

First you see the low population-low morbidity stable-state of the hunter-gatherer society. Per unit productivity is low, keeping a check on the maximum carrying capacity. But because populations are dispersed many of the infectious diseases which we take for granted are simply not issues for hunter-gatherer bands. Next you see the transition to agriculture. This increases per unit productivity by a order of magnitude, resulting in a situation of “land surplus.” A huge population explosion follows, and now the stage is set for the rise of infectious diseases. As the population reaches carrying capacity individuals are under nutritional stress. Additionally, the agriculturalists will also no longer have access to game & herbs to supplement their calorie-rich but micronutrient and protein poor diets. They’ve given the land over to raising enough food to maintain their population. Now diseases of mass agriculture begin to spread, and the new farmers have no resistance. Already subject to greater morbidity because of the nature of their diet, they become victims of a pandemic.

In classic Malthusian fashion morbidity abates as population density declines. Additionally, the survivors will now have some immunity to the infectious agents. We are past “peak morbidity.” Evolution also now begins to select individuals who are more well adapted to the rigors and stresses of agricultural life. The population reaches carrying capacity again, but though morbidity is still above the hunter-gatherer stage, it does not hit its previous high.

This does not prevent populations from being beset by “exogenous shocks.” A famine results in a sharp population reduction, but after the environment becomes favorable again the population bounces back. Also, the temporary land surplus benefits the survivors.  Despite the power of “endogenous” parameters, there are always going to be periodic random environmental catastrophes or windfalls modulating the population size and average well being.

Finally, a secondary “agricultural revolution” occurs. A new innovation, most likely a superior cultivar or food crop, arrives on the scene. Like the original transition to agriculture you see an immediate per unit increase in productivity. This means that there is a practical land surplus. Because the population is now “catching up” to its carrying capacity the morbidity drops again. What happened in Ireland in the 18th century, or in China after the “Columbian Exchange,” may be modeled by this phenomenon. Finally the population is at a new higher carrying capacity.

Even this is simplified. But I think it takes into account the reality that both biology and culture evolve. And it may explain some of the shifts outside of the standard Malthusian economic model, which assumes a relatively static technological environment.

CATEGORIZED UNDER: Agriculture, Anthroplogy, Culture
  • http://contemplationist.wordpress.com Contemplationist

    Excellent model Razib. This is pretty supportive of the Paleo diet claims I gotta say.

  • Simplicio

    @Contemplationist: It’s supportive of a Paleo diet being healthier then that of a Neo-lithic farmer’s diet. It doesn’t really say anything one way or another about if a Paleo-diet is healthier then a Modern Western diet.

    The modern Western diet doesn’t have the same problems (we don’t rely on a single staple crop, for example, and have figured out how to limit the lethality of most infectious diseases), and indeed, we’ve finally regained the height we had in the paleolithic. We’re sort of in the extreme case of the effect Rahib theorizes existed in 19th century Ireland and other places, we’ve perfected agriculture and “dense living” to the point that most of the problems associated with it no longer exist.

    So while there might be reasons to think a paleo-diet is healthier then a modern one, I don’t think this article provides one of those arguments.

  • http://blog.cholesterol-and-health.com Chris Masterjohn

    May I put your graph on my blog (http://blog.cholesterol-and-health.com) if I properly attribute it to you and link back to your blog?

    Thanks,
    Chris

  • Sandgroper

    This is really getting off the topic somewhat.

    In addition to a more varied diet that was better nutritionally, hunter gatherers were relatively disease free, not just because of nutrition, but for other reasons as elucidated in the post.

    Plus you have to think about the fact that evolution has not stopped – think about lactose tolerance and what Razib once referred to as a “hammer blow of selection”.

    If people are lactose tolerant, what makes you think they are any longer particularly adapted to a hunter-gatherer diet, or that they would be better off cutting dairy foods out of their diet?

  • DK

    How about this: nutrition has little to do with any of it? Agriculture, being a great innovation, lead to the population explosion by allowing smaller, weaker and less healthy people to survive and propagate. Same logic with epidemics. Most epidemics require critical population densities (= cities, advanced civilization). Also, animal husbandry catalyzes new infectious strains.

  • http://blogs.discovermagazine.com/gnxp Razib Khan

    #3, yes.

    #5, yeah. that’s not impossible. one can also imagine that HG pops had more between group conflict, with smaller groups.

  • Johnny Bourdeaux

    Obviously, the overall lifestyle changes were of great importance. However, diet almost certainly had an important role too. Grains tend to be rich in phytates that impair the absorption of nutrients (ie Vitamins ADK2), and minerals in particular. Some of the anti-nutrients in grain have been shown to impair vitamin D metabolism which is not good news bearing in mind vitamin D plays a key role in the functioning of calcium in the body. Grains also contain substances that impair digestion, and these won’t help matters either.

    Several controlled experiments have shown, that health parameters can improve on a grain free diet, including dental health. It’s still unknown, how much this is because specifically grains and other factors that changed.

  • John Emerson

    A factor leading to the smaller but better fed population of hunter-gatherers: because hunter-gatherers tend to be mobile, and they tend to rely on meat, they don’t have stores of food (grains, legumes, and root crops like potatoes ) to get them through a bad season or a bad year. Food shortages come in the form of rather quick die-offs (a few bad months) punctuating longer periods of relative abundance for a population which has been kept small by the die-offs. And presumably during these die-offs children would die early on and wouldn’t grow up stunted. (The Inuit had an actual protocol for this: old people starved first, then children, then women, then men).

    A factor stunting agricultural peoples: peasants are by definition not mobile, especially once the good land is all in use. For this reason they are at the mercy of a well-organized military force, and imperial tax collectors would tend to keep the peasantry at the bare subsistence level regardless of agricultural productivity or population levels. In kind taxes/rents on peasant farmers could be as high as 50%.

  • Sandgroper

    “they tend to rely on meat”.

    No they don’t. Ask Greg Laden, who actually knows something about this. The Inuit are atypical in this due to their particular environment. In the general case, HGs are highly mobile to take advantage of seasonal abundance of both plants and animals, and it is the need for mobility of the whole group that is a constraint on both old people and reproduction.

    Agricultural people also had seasonal famines and bad years, often multiple bad years in a row. This was an incentive to improve methods and crops. HGs have their own incentives to find ways to encourage both food plants and prey animal abundance, but less scope for innovation.

  • Eurologist

    “because hunter-gatherers tend to be mobile, and they tend to rely on meat, they don’t have stores of food”

    Of course they do, in abundance. Dried berries, dried fruit, dried tubers and mushrooms, fresh fruit and tubers that last, dried fish, dried and smoked fish and meat, stored animal fat, nuts, and even collected grains – to name a few. Just because they were mobile does not mean they did not have permanent albeit seasonal settlements. Add to that frozen food during cold times / the ice ages.

  • John Emerson

    Granting the point about meat vs. plant food. Yes, HGs are highly mobile to take advantage of seasonal abundance, but famines are during times when there’s no abundance. Eurologist’s list gives a large number of different kinds of stored food, that kind of abundance, but that doesn’t mean that the quantities were large, and the permanent camps didn’t have warehouses. Several bad years in a row will decimate an agricultural people, but my point is that a much shorter famine will have the same effect on a hunter and gatherer people. Furthermore, hunter and gatherer peoples usually are not part of larger political or social entities from which help might possibly come, or to which the starving might flee.

    The nut of my argument is that hunter and gatherer peoples have less capacity for storing food than agricultural peoples and thus can be decimated by a much shorter famine, and partly as a result of this, are seldom near the Malthusian limit during the good years.

  • Sandgroper

    “hunter and gatherer peoples usually are not part of larger political or social entities from which help might possibly come”

    At least in Australia, they had trade and communication networks covering long distances. Agreed it’s not the same thing, but they were part of larger social entities of a sort.

    A lot of the early European explorers in Australia were kept alive by Aboriginal people when they got themselves into trouble, so they had the culture. Undoubtedly, Aboriginal culture embodies the concept of giving what you can give to people in need, even strangers.

    When you can subsist on a wide variety of species, you may be less vulnerable to short term climate fluctuations, particularly if you are below the Malthusian limit in times of abundance. It’s not like they were unfamiliar with the phenomenon of drought, and they had oral histories. Again, it’s not the same thing as a large collective grain store centrally administered, but it gives some dimension of robustness. Presumably for farming communities the taxes went at least partly towards building in this community preparedness. It’s not a totally unreasonable system – it puts some curb on people producing too many children, and makes provision to feed the community in bad times.

    Those are not really big points against, but I just mention them for completeness.

    I see other factors at play in keeping HGs below the Malthusian limit, though – infanticide, mortality through violence, etc. Aboriginal people practised infanticide and had at least notional birth control practices, because a woman could carry only one child over long distances. Whether it was also from some notion of keeping the group down to a number that won’t overtax the available resources is maybe stretching it, it begins to sound like a just-so story. But for HGs who rely on being highly mobile, it really amounts to the same thing.

    But it doesn’t do to generalize. And I get your main point – farming is intuitively a more reliable and predictable way to get a steady supply of food, albeit with much less variety and nutritional value. To an HG who is frequently going hungry and dependent on sources that are frequently unreliable, that would seem valuable. It did, that happened in Australia, Aboriginal people went nuts over biscuits, refined flour, sugar, jam and tea that they could get from whitey in steady predictable supply.

  • Trevor Watkins

    I shall be interested to see the sample sizes in the studies synthesized in this paper. From what I know, in Europe and southwest Asia, the numbers of burials from the pre-agriculturalist period are very, very small – maybe too small to be used as the base for measuring the impact of the arrival of farming, or colonising farmers. Again, from what I know, the pre-Neolithic burials are so few at any one place that it seems to me that there is a good possibility that some kind of selection has taken place or at least that the sample that we have does not represent a representative sample of the population.

    And I am also unhappy at the direct linkage of stature/robusticity to diet. There was another factor involved with the transition to farming in many parts of the world, namely that people began to live in much larger, denser and permanent concentrations, and they lived in close proximity to their animals. The opportunities for communicable diseases were greatly enhanced, as the opportunity for diseases to cross from animals to humans. Was decreased stature and robusticity in the working class urban populations of the industrial revolution a consequence of poorer diet than farm labourers had enjoyed? Or was it a combination of poor diet and poor living conditions?

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This blog is about evolution, genetics, genomics and their interstices. Please beware that comments are aggressively moderated. Uncivil or churlish comments will likely get you banned immediately, so make any contribution count!

About Razib Khan

I have degrees in biology and biochemistry, a passion for genetics, history, and philosophy, and shrimp is my favorite food. In relation to nationality I'm a American Northwesterner, in politics I'm a reactionary, and as for religion I have none (I'm an atheist). If you want to know more, see the links at http://www.razib.com

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