Over at physicist Steve Hsu's site Information Processing blog, Ron Unz digs up a three decade old term paper he wrote as a Harvard freshman when he persuaded Edward O. Wilson to give him an independent study course on sociobiology. (By the way, Harvard is always criticized as an undergraduate experience for having a glittering faculty who turn out to have no time for lowly juniors and seniors. If you are Ron, though, you just show up as a freshman and talk the world's most prominent biologist into giving you personal service.) Ron sums up his thesis in 2011 as:

Preliminary notes on the possible sociobiological implications of the rural Chinese economy ... (B) The idea is a very simple one, and I'd actually gotten it a couple of years earlier when I was taking a seminar on the rural Chinese political economy back at UCLA. Chinese society had several fairly unique characteristics which together probably caused the evolution of high Chinese intelligence.

(1) For many centuries and to some extent for a couple of millenia, Chinese peasants lived close to their Malthusian limits. The orderly, stable, and advanced nature of Chinese society meant that food supply and poverty were usually the limiting factor on population, rather than wars, general violence, or plagues.

I think this makes some sense. A high disease burden caused by, say, malaria-bearing mosquitoes as in tropical Africa before recent times probably isn't good for selecting for foresight because behavior doesn't have much impact on who lives or dies because who gets bit is pretty random. Instead, selection would be focused on developing defenses against diseases. On the other hand, Ancient Egypt would seem like a similarly "orderly, stable, and advanced" peasant society, but the outcomes don't seem very similar.

(2) Chinese rural life was remarkably sophisticated in its financial and business arrangements, vastly more complex and legalistic than anything you would find among European peasants let alone those in Africa or elsewhere. Hence there was obviously huge selective pressure for those able to prosper under a system of such (relative) financial complexity.

Perhaps, but the the English Common Law, which governed property in England was not easy to understand. It's kind of a medieval programming language for writing contracts full of If-Then-Else statements.

(3) Virtually all Chinese were on an equal legal footing, with none of the feudal or caste legal districtions you would find in Europe or India. Successful poor peasants who acquired wealth became the complete social equals of rich peasants or landlords. Rich peasants or landlords who lost their wealth became no different from all other poor peasants.

(4) In each generation only the relatively affluent could afford to marry, e.g. have parents wealthy enough to afford to buy them wives. The poor couldn't obtain wives for their children, hence didn't have grandchildren.

My impression is that this was true in China from the male perspective. From the female perspective, the great majority of women married, and married young. In contrast, English women who were poor for their class tended to marry late and have fewer children. I don't really know what the implications of this would be.

(5) The unique Chinese custom of "fenjia" meant that land, i.e. wealth, was equally divided among all sons. Since the wealthy tended to have several surviving children, those children automatically started life much poorer than their parents, and needed to reacquire wealth through their own ability. Because of this system, rural Chinese society exhibited an absolutely massive and continual degree of downward social mobility, perhaps unprecedented in human history. Each generation, a good fraction of the poor disappeared from the gene-pool, while the wealthy generally became poor. The richest slice of the population could afford multiple wives and numerous children, but due to fenjia this just tended to impoverish their families to a compensating extent.

I think the idea here is that if you have Five Chinese Brothers, they each inherit 1/5th of the land of their father, and then each must hustle like crazy to make a living. Maybe Number Four Son turns out to be the most fit and has the most descendants. In contrast, under English primogeniture, the eldest son gets the land, so he can probably afford to marry even if he's no great shakes because he's not competing at farming with his younger brothers. The younger sons go into other fields and have to hustle to marry. So, there's more immediate selection on farming talent in China than in England, where the eldest son gets something of a free ride for a generation. But maybe the English system selects for more eccentricity or whatever by forcing younger sons to try to make their way in the world in some other fashion than being a landowning farmer.

(6) The smartest children of the wealthy often received specialized education in hopes they might pass imperial exams and thereby join the "gentry," which might greatly increase the future economic prospects for themselves and their close relatives. So there was indeed some "pull at the top" but I think the genetic impact was pretty small compared to the "push from the bottom."

Right, the number who strongly benefited in terms of offspring from the imperial examination system were a tiny fraction.

(7) Overall, the model is pretty similar I think to what that [Gregory] Clark fellow wrote about England. However, I think the degree of genetic pressure in each generation was enormously greater, fenjia caused automatic downward mobility each generation, and I think the system remained in place for several times longer than the few centuries Clark claims for England. So you'd expect the results to be much greater.

(8) One very important difference with the Cochran-Harpending model for the Ashkenazi Jews of Eastern Europe is that the selective pressure was multifaceted. Ashk Jews merely needed to be smart and make money in order to become selectively advantaged. However, the selective pressure on Chinese peasants pushed in lots of different directions simultaneously. Peasants needed to be smart and have good business-sense, but they were also being selected on the basis of physical endurance, robustness, diligence, discipline, energy-consumption, and lots of other things. So selection for intelligence couldn't come too much at the expense of other vital traits, hence took place much more slowly.

Another question would be how significant was the impact of urban life on the Chinese. Marco Polo marveled at the size of Chinese cities compared to European cities. Finally, my vague impression is that the Malthusian hammer tend to come down on the Chinese more intermittently. Because the full baby-making capacity of females was utilized, Chinese population would grow faster during good times than English population. But when good government broke down and troubles hit, there would be huge die-offs (as recently as the Great Leap Forward). Unfortunately, I don't have a picture in my head for understanding the implications of selection by famine as opposed to selection by constant hunger.