Interesting theory. The Chinese are fully aware of the "north-south" differences themselves, although they often attribute it to other reasons, such as legacy effects of numerous mongol/manchu/other "barbarian" invasions from the north through out China's history, which often times were stopped around the Yangtze River. This resulted in the north under "barbarian rule" for long period of time, while the south held refugees of original ethnic Han chinese from the north.
> Talhelm said that one of the most striking findings was that counties on the north-south border – just across the Yangtze River from each other – exhibited the same north/south psychological characteristics as areas much more distantly separated north and south.
This from the original article seems to support your "invasion stopped at Yangtze" theory more than a "rice/wheat divide" theory. Rice is grown north of the Yangtze also and the border seems to be on the hills between provinces such as Hubei and Henan.
Interestingly, I've always been taught that the difference is explained because of dryland farming vs irrigated farming (so essentially, rice vs wheat), which leads to difference in development of agriculture and so on. I'm actually surprised that there doesn't seem to be a consensus about that yet.
William McNeill, in Plagues And Peoples [1], makes the point that there are disease gradients that strongly influenced the movement of peoples and the development of culture, and that this gradient in China maps almost precisely to the rice/wheat border. Southern peoples had, by virtue of the ubiquity of disease vectoring mosquitos, an inbuilt defense against even massively superior Northern armies. This may be in large part why the Mongols took so long to conquer the Southern Song, and why Vietnam was able to successfully resist them.
