Group lifespan differences? Maybe it’s agriculture
Economists Oded Galor of Brown and Omer Moav of Hebrew U. argue in a new paper that the Agricultural Revolution created longer lifespans. A simple version of their model goes like this:
Agriculture–>Disease–>Somatic Investment in stronger bodies–>Longer lifespans once things settle down.
This result hoists Jared Diamond on his own petard: If the Agricultural Revolution really did make life worse (as he frequently argues), then the forces of evolution would have noticed that fact and reacted in some way. Galor and Moav argue that evolution would respond by building stronger bodies in high-disease environments, and the result would be longer lifespans once those dangers of disease recede in the modern world.
More importantly, Galor and Moav argue that we’re still living through the Agricultural Revolution: Groups that went agricultural early on went thorough bigger genetic changes. That means that early agriculture should cause longer lifespans.
An interesting theory, but what’s the evidence? They use Putterman’s new estimates of the year that countries went agricultural, control for a lot of the usual suspects, and find this:
[C]ontrolling for geographical and continental characteristics of each country, as well as income, education and health expenditure per capita, every 1000 years of earlier Neolithic transition contributes to life expectancy 1.6-1.9 years.
A couple of facts about the agricultural transition: The differences across countries are big, according to Putterman:
The average country went agricultural about 4500 years ago (mean and median within a couple of hundred years).
Standard deviation: 2400 years.
10th percentile: 1500 years ago (mostly sub-Saharan countries, plus some New World countries)
90th percentile: 8000 years ago (Eastern and Southern European countries–the Middle East was earlier).
So the cross-country differences appear big enough to be evolutionarily important a priori.
But back to Galor and Moav’s big result: Almost 2 years of life for a thousand years of agriculture: Maybe that number will become a new stylized fact in the economics-and-evolution literature. It’ll be interesting to see if this result comes up in political debates over health care reform…..
Galor and Moav argue that evolution would respond by building stronger bodies in high-disease environments, and the result would be longer lifespans once those dangers of disease recede in the modern world.
This seems unsupported – I thought the “antagonistic pleiotropy” theory was that things that help you when you’re young will hurt you when you’re old (e.g. tesosterone makes you stronger in youth, gives you prostate cancer when old, etc). So a high-disease environment could _lower_ lifespan limits by favoring genes that help you survive long enough to reproduce, but then kill you once you’ve shot your fitness wad (so to speak).
tc, that is my first thought too. i’m going to dig deeper into the paper and come back with a comment. if anyone needs an example of what tc is talking about, think sickle cell anemia or cystic fibrosis. there is some benefit in the het. state that increased the frequency of the derived alleles (in sickle cell it is malaria, which became endemic after agriculture).
tc,
Indeed–Galor and Moav push hard for somatic investment–a win-win story–over a more brutal (and more economic-sounding) trade-off story.
But where there are puzzling facts to be explained–like big differences in average life expectancy across countries and “continental groups” that persist even after controlling for the usual suspects, it’s time to try some theorizing…..So I welcome their efforts.
It’s more likely an increasing degree of adaptation to a high-carbohydrate diet. There are other factors worth considering: wimp neurological adaptations that decrease interpersonal violence,
maybe differential resistance to undiscovered or poorly understood pathogens involved in chronic diseases. Selection for increased IQ could also increase lifespan summat.
I haven’t really read this properly, but I note that the main determinant of life expectancy (at birth) in pre-industrial societies is the level of infant mortality. Typically, about 1 in 3 babies die in the first year, and cumulatively about 1 in 2 by the age of 15. Those who get over the perils of childhood have a reasonable expectation of getting to age 60 or more.
David, if you take people who were very recently hunter gatherers and put them into a modern society, then infant mortality drops to about the same level as the surrounding society due to modern health care, but as adults they suffer higher rates of chronic diseases like Type 2 diabetes and such. There are other factors which help to explain shorter life expectancy, like poorer standards of health care later in life, poorer living standards generally, drinking problems and such, but it seems very evident that a high carb high glycemic index diet affects them particularly badly.
Such a group are already descended from those survivors who had natural immunity to the diseases that killed off all of their contemporaries when they first came into contact with Europeans, so I suspect Greg Cochran is right about progressive adaptation to a high carb diet.