The article makes a good case for why agriculture could be more important than sunshine: the sun doesn't care about the Yangtze River as a border.

Nice try, but Yangtze River happens to be at the dividing line of north/south, not strictly but close.

Not at all. There have long been obvious differences between north and south china, but the Yangtze isn't the border between North and South, it's the heart of the South. North China is divided from South China by the Huai river (http://en.wikipedia.org/wiki/Huai_He).

Chinese civilization is essentially the story of intensely farming a flood plain. But China has two such plains: the Yellow River defines the north, and the Yangtze defines the south.

so... you agree with me? I don't get your point.