... (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.
(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.
(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.
(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."
(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.