Monday, March 19, 2007

Galor and Moav: Property rights as an evolutionary force   posted by Herrick @ 3/19/2007 12:32:00 AM

Recently, I've posted on economists' attempts to use genetics to explain long-term economic growth. So far, I've talked mostly about data. Today, theory gets its due.

Oded Galor (Brown) and Omer Moav (Hebrew U and Royal Holloway) have a simple story: The agricultural revolution set off a process of rapid human evolution that itself created the industrial revolution.

The longer version: In a hunter-gatherer society, everything's a team effort. Each day's successes and failures are shared with a fairly large clan. That provides insurance, which is quite valuable. However, since there's no "I" in team, that means that in a hunter-gatherer world, evolution can only work at the group selection level. And as Razib has noted, group selection is simply a weaker force than family-level selection.

Then comes the agricultural revolution. Such a world, they say, led to the rise of the nuclear family as the unit of production, as the unit of wealth transmission, and hence, as the unit of evolutionary selection. More productive nuclear families, working on their own plots of land, were wealthier and hence healthier and hence passed on more of their genes into future generations. The end of insurance meant the end of group selection.

In the main body of their paper, Galor and Moav emphasize the "quality v. quantity" choice as the key evolutionary choice: Parents who chose to have lots of kids would pass on fewer genes, while parents who chose to invest more in the education/nutrition of a smaller number of kids passed on more of their genes. So the "choosing child quality" allele become the favored allele. However, they explicitly note that they could have just as easily written the model as one where more intelligent offspring were more productive.

My subject line is disingenuous: Galor and Moav nowhere claim that property rights were an evolutionary force. However, they do need some mechanism in their model to move them from the group-sharing of the hunter-gatherers to the family-sharing of the agriculturalists. "Property rights," whether tacit or explicit, seem to do that just fine. What's mine is (sorta) mine, even if the king takes half and I share some with my neighbor. Still a far cry from the hunter-gatherer world.

It's easy to see how this theoretical model can fit into a Diamond-style Guns, Germs, and Steel model: Regions of the world that have more easy-to-domesticate plants and animals ex ante (e.g., Eurasia) have a more thorough agricultural revolution, which leads to more rapid spread of the human-capital-promoting alleles throughout the population ex post. Rice begat 'rithmetic.

Galor and Moav's paper, "Natural Selection and the Origin of Economic Growth," was published in the Quarterly Journal of Economics (a top-5 econ journal) in 2004. A working paper version is here. A less-technical review of the new field that Galor and his coauthors created, known as "Unified Growth Theory," is here. Section 5.2 of the latter paper gives a quick overview of their theory. The closing paragraph of the review is worth citing:

The most promising and challenging future research in the field of economic
growth....would be the exploration of the interaction between human evolution
and the process of economic development.