If I may, an alternative theory.

Chinese countryside after 1949 was a collectivized hell (similar to that in the Soviet Union after collectivization in 1930). Life in the kolhoz (or its Chinese equivalent) is quite similar to serfdom (Soviet peasants had their passports confiscated until 1960s, officially 'for safekeeping). Peasants were the most exploited part of the population, facing the hardest consequences (the great chinese famine, Holodomor, soviet famines of 1921, 1946-47, just to name some of those).

Therefore, it was the best interest of any Chinese (and Soviet) peasant to leave the countryside for the city. Or, if not possible, at least ensure that the children move to the city after finishing school. This would result in massive self-selection, and correlation with IQ is quite possible.

In the "West", the situation is the opposite - the "best" can stay in the countryside (let's say, the most capable son staying in the family farm), while the outcasts, adventurers and "surplus population" leave for the city. In this situation, correlation with IQ is less likely.

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> publish first, think later, great strategy for a successful blog!

Most people are too disorganized and tolerant of sloppiness for this to work, but for you, definitely. Readers don't (always) need a definitive conclusion; they want to get to know you, see your evolving thought processes, and be exposed to stimulating ideas.

> If cities are population sinks which are dependent on a constant influx of people

> and genetic material from the surrounding countryside it is very difficult to talk

> about a specifically urban evolutionary history.

Well, only if 1. there's zero gross migration out of the city, and 2. urban graveyard effects don't exist elsewhere. Even though net migration may all be inward, some individuals can make their way outward to influence the source population.

> Studies of the urban graveyard effect in China are, perhaps not surprisingly, thin on the ground.

Too bad - but there *is* a general sociological principle that subsistence style impacts fertility. Foragers have lower fertility rates, then pastoralists and horticulturalists, and then agriculturalists have the highest rates because of the way children provide an excellent pool for low-skill labor which is at a premium for sedentary farmers. Moving forward, birth rates decline in part because the cost/benefit ratio tilts away from large families, and we see this in the ongoing demographic transition today. Essentially, urbanites are further along the demographic transition than rural farmers, so even without data, it seems pretty safe to assume that the urban graveyard effect wasn't merely isolated to Britain.

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There also problem that Mandarin class of scholar-officials is not truly urban people, Mandarin is landlords with rural income and estate.

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There is one thing I don't get here: Why not assume that the Chinese countryside experienced a great brain drain in the 20th century? If so many people successfully moved into the cities after 1949, couldn't those migrants have been more intelligent than the average countryside person?

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