Here's why I'm skeptical of the Communism explanation: The former East Germany produces much more patents per capita than Portugal, southern Spain, and southern Italy even though the former East Germany was previously under decades of Communist rule whereas these other regions were not.Yeah, I was going to say, the border between things was very reminiscent of the old Iron Curtain line in Europe. As such, I feel like the recent destructive influence of Communism that is barely a generation removed might have a greater impact immediate impact as opposed to genetic drift.
Also, does China and Japan have similar prohibitions on cousin marriages? As both countries historically have been highly innovative, Japan especially in the 20th century.
As for China and Japan, Yes, they both have relatively low rates of cousin marriage:
The individual & social risks of cousin marriage
Southern Indians have much higher rates of cousin marriage.