Sunday, November 11, 2007

Group lifespan differences? Maybe it's agriculture   posted by Herrick @ 11/11/2007 10:26:00 AM

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.....

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