In the comments below there was a mention of the fact that East Eurasians are less genetically varied than people to their west. The main reason for this is probably the serial bottleneck of modern people as they left Africa/Near East ~50,000 years ago. Similarly, people of the New World and Oceania are also less genetically diverse, because they’re at the “end of the line.”

But, that doesn’t mean that East Asian populations were particularly small after the founding compared to West Eurasians. It’s simply that genetic diversity over the long term is sensitive to bottlenecks, rather than rolling census counts (long term effective population is a harmonic mean).

With that taken care of, I think we need to be open to the possibility that the peculiar patterns of population expansion in East Asia could be a function of its Pleistocene paleoecology. From what I know in biogeography temperate China is more speciose in trees than temperate Europe. The reason offered is that China had more “ecological depth” due to its geographic configure. During the “Last Glacial Maximum” areas of Europe suitable for forests retreated and disappeared as the Mediterranean blocked further progress. In contrast, China expands in a continuous zone far to the south and east.

European hunter-gatherers have noticeably low genetic diversity and repeated population turnovers. The Mesolithic peoples of Europe were themselves the product of a late Pleistocene expansion, and quite genetically homogeneous (these groups “break” the iron correlation between distance from Africa and homozygosity). It seems plausible that European Pleistocene populations drew from a much shallower demographic reservoir than East Asian ones. This, to me, may explain why population turnover and lineage expansions were a more common feature of the West Eurasian landscape than in East Asia, where the local hunter-gather cultures came through the Ice Age with more robustness and deeper roots.

Well, at least part of the reason. I doubt it explains everything…

Note: You may wonder why I posted a photo of David Epstein’s Range: Why Generalists Triumph in a Specialized World. I’m to a great extent generalist. I know enough pop-gen to have an intuition about effective populations and genetic diversity, as well as enough human genomics background and experience to know the empirical distributions. When I was eight I spent a fair amount of time reading about climate science, and so know the Koppen system to this day and the differences between temperate Europe and East Asia (maritime vs continental as well as huge latitudinal difference and why). Finally, at some point in college, I was interested in biogeography and read a paper that explained why species richness varies across the two temperate (non-boreal) zones of Eurasia.

And that’s how this post came about.