Thursday, October 16, 2008

Lions and antelope   posted by Razib @ 10/16/2008 12:45:00 AM

Sandy has a post up, Why Do Women Have More Cavities?, where he reviews the John Lukacs paper I pointed to yesterday. He says:
So ultimately female physiology combined with the the changes in diet and increased feritlity are the reasons why women have more cavities than men. Razib mentions that with increased fertility comes a reciprocal increase infant mortality, especially because the agricultural revolution increased communicable diseases. He concludes that hunter-gatherer infants are far more likely to reach reproductive age than infants of an agriculturalist.

But I disagree. Despite the recent popularity of the paleo-diet, the real hunter gatherer lifestyle is not easy. Many hunter gatherer societies have erratic sources of nutrition, very few have regular caloric intakes. John Hawks explained that among hunter gatherers, like the Hiwi, only 43% of the adults were expected to see the age of 30. Furthermore, many hunter gatherer cultures also have food taboos which dictate the diets of females. For example, Australian aboriginal societies restrict protein and fat foods for pregnant and lactating women. Similar traditions exist in Africa too. In Athapaskan societies, females at menarche cannot eat fresh meat.

Mothers who do not consume many calories, reach menarche at an older age and become amenorrheic - irregularly menstruate. If and when they do have a child, they are often of low birth weights, and have a higher risk of dying because they have little to no fat reserves. They consume inadequate amounts of nutrition since the mothers cannot make insufficient amounts of milk. All of which influences birth spacing significantly.

Despite the increased probability of cavities, the Neolithic revolution has generally been a good thing for women and children.

I mentioned in the comments that I'm pretty sure that he misunderstood me. So I'll clarify my conception in this post. Unfortunately, though I'm obviously interested in this particular topic (you know this if you read the blog) I'm not that familiar with the cultural anthropological literature, so all my assertions are very provisional because I don't feel confident I know the literature well. Nevertheless, in regards to my basic logic I'm confident that if Lukacs and others are right in regards to birthrate, what I said has to be true.

Here is what I said:

... In contrast, hunter-gatherer women typically have a reduced number of pregnancies because of behaviors such as extended breastfeeding. Of course, most agricultural societies quickly reached the Malthusian limit (ecological carrying capacity), so the higher fertility was likely balanced out by higher infant mortality. If agricultural women gave birth to more infants a greater proportion of these offspring ended up dying of diseases, etc., than for hunter-gatherers. So at birth any given hunter-gatherer infant is far more likely to reach reproductive age than any given offspring of peasants....

I was careful with the words I used here. I was working with a Malthusian assumption in regards to pre-modern populations. In short, most of the time populations did not exhibit the sort of long term sustained growth rates of the last few centuries. In medieval England, where we have some documentary demographic sources, we know that the population crashed during the Black Death and didn't reach its pre-crash peak for over two centuries. I recount this to make clear I do understand that the flat population growth curves you see for pre-modern demographics are generally "smoothed" and there were wild local fluctuations. But, these fluctuations oscillated around an "ecological carrying capacity."

There is of course another dynamic which occurs some of the time. If, for example, a human population discovers new territory where there is a surplus of land and Malthusian pressures are minimal, you will see a transient logistic growth curve. That is, population will increase up the Malthusian limit, what biologists would term the "carrying capacity." The United States during the period between 1650-1850 is a really good case for this. The number of white Americans rose because of immigration, yes, but there was a very high endogenous rate of growth driven by natural increase. In Albion's Seed David Hacket Fisher reports that in New England there were many towns where the average number of live births in a woman's reproductive span was north of 10! This is of course feasible when you have such a asymmetry between land, resources from which humans can derive sustenance, an the number of humans. Not only were New England families fertile, but European observers such as John Crevecoeur commented upon the relative physiological health of Americans during this period compared to those of the British Isles or the Continent (large, plump, vigorous). When you are below the Malthusian limit there is far less constraint on resources and so individuals are at their nutritional optimum.

Carrying capacity does vary as a function of ecology and culture. There is a reason that Yangtze delta was more densely populated than European Russia in 1700; not only is rice more efficient at producing calories from any unit of land in comparison barely, wheat or oats, but the climate in that region of China allows multiple croppings over the year. These sorts of ecological parameters are common sense. But though the population density might differ by around an order of magnitude, Russian and Chinese peasants had a similar quality of life (though there is differences on the margins, they are not predicted by the difference in density). This is because both populations were pushing up against the Malthusian limit, or carrying capacity, of their locality.

When you compare agriculturalists to hunter-gatherers, you will likely know that the former live at higher densities than the latter. You will also know the former to be far more sedentary than the latter. This is not strictly a function of ecology; almost all regions where agriculture came to dominate were once inhabited by hunter-gatherers. In fact, there is plenty of evidence that many of the latter switched lifestyles to become farmers. Sometimes the process could take some time, for example there is a fair amount of archaeological evidence in southern Sweden that non-agricultural societies had a flourishing trade with agriculturalists for thousands of years. Why so long for the switch? The crops of the Middle East emerged in the Middle East, and so the cultural toolkit took some time to evolve so that it was attractive and preferable to northerners.

Why did hunter-gatherers become farmers? One can posit many reasons. But remember what I said about the logistic growth along the transient? This can take some time. We in the United States don't really know how long it would have taken America to "fill up" so that the European misery index was recapitulated among Yankee yeoman (the frontier did not close until almost 1900). The demographic transition in the late 19th century changed the whole game. If you are a hunter-gatherer, and you see that your neighbor can extract many more calories out of a smaller amount of land and so have a larger family, it might seem like a rather rational choice. If thinly scattered hunter-gatherers switched to agriculture they would slide along the transient of the logistic growth curve for many generations. In fact, the early adopters would never know of the misery which later generations would take for granted! The cultural invention of agriculture changes the whole game, at least temporarily. But eventually the law of diminishing returns kicks in, an the balance between land and population returns. The stationary state has been achieved.

And it is because of the stationary state that I said what I said about fewer offspring reaching reproductive age. If a population is stable then parents only replace themselves. This is true whether one is a hunter-gatherer or a farmer. But, what about Lukacs' assertion that females in agricultural societies had a higher birth rate? Well, naturally then there must have been a higher mortality rate. That is why I referred to pregnancies; if hunter-gatherer women space their births through weaning an abstinence then they might have had many fewer pregnancies than the wives of farmers. But if both populations were at the Malthusian limit the surplus must be "pruned" by mortality, and more surplus implies greater mortality.

Why did hunter-gatherer women wish to space their births? The general hypothesis is that mobile groups need to maintain a reasonable ratio of productive adults to very young children. A hunter-gatherer woman would have had a more difficult time of managing multiple toddlers because of the need to move them on occasion. In contrast, a woman living in a village might be able to manage with multiple toddlers. Additionally, once the children reached the age of 5 or 6 they might have been economically valuable producers. If many of them died of disease before they reached the age of reproduction then the society could gain their production without having to worry about them contributing to higher population growth or taking care of them in their dotage.

As for all the stuff about how miserable hunter-gatherers were, that's pretty much irrelevant without a reference point to the misery of farmers. As I said, I don't know the literature very well. A Malthusian model should predict basically the same wealth for hunter-gatherers an farmers over the long term. That's close to what Greg Clark in Farewell to Alms assumes, though there are qualitative differences in the way farmers consume and hunter-gatherers consume. Life is not a continuous trait, you're alive, or your'e not. Farmers tend to have much less diverse diets than hunter-gatherers for rather obvious reasons. Because of the density of villages an the emergence of higher order social structures which foster more trade and commerce farmers are subject to more powerful epidemics. It seems though that hunter-gatherers often live violent lives, and without economies of scale and recourse to mass social collective action they might be more vulnerable to various types of environmental perturbations over the short term. In other words, these two pre-modern groups both lived like crap compared to today, but somewhat differently.

From all I have read if called on to give the quality of life award to either lifestyle anthropologists would today seem to tap the hunter-gatherers as being on top. It isn't just about dental carries. Farmers are physically smaller and exhibit more evidence of chronic nutritional stress than hunter-gatherers (that is, comparing remains from a locality which made the transition across a span). As noted in some of the papers below the higher fertility of farmers was almost certainly balanced by a higher mortality; a conscious human at the age of 5 seems to have had a greater likelihood of dying early among farmers because there were just more of them floating around.

Here are some papers to support the above claims (more or less):
The origins of agriculture: Population growth during a period of declining health
Biological Changes in Human Populations with Agriculture
Testing the Hypothesis of a Worldwide Neolithic Demographic Transition
Agents Adopting Agriculture:Modeling the Agricultural Transition

If you're a cultural anthropologist who knows more about this please add citations and results in the comments, I'm curious but I don't have the time to really familiarize myself with the literature to make strong judgments. Don't be a CAFR and ramble on about something you don't know about or spend 12 paragraphs on problematizing the word "farmer."

Note: The title: I sometimes think of hunter-gatherers as lion and farmers as antelope. There are many more of the latter because there's a lot more grass than antelope. Additionally, if a lion gets injured there's no way they're going to catch an antelope, it's a high risk profession. But who would you rather be? Note that the European aristocracy generally hunted as opposed to gardened. See Tim Blanning's The Pursuit of Glory: The Five Revolutions that Made Modern Europe: 1648-1815.

Addendum: Unfortunately, this isn't for pre-modern populations necessarily, but I thought readers would find this chart of interest....