What if it's due to neither environmental nor genetic factors but ideas. Europe was backward until it re-absorbed classical learning and absorbed newer ideas from the Orient, which led to the renaissance and everything that followed. Did Europeans suddenly gain 40 IQ points in that time? No. Did their environment change? No.

For some reason a lot of people have a huge problem with this explanation, actually preferring either environmental determinism or racism. This is in spite of what seems to be a lot of historical evidence for it in the form of causal influence: ideas are introduced somewhere (inventions, methods, philosophies, languages, mathematics, literature, etc.) and large changes follow.

His entire section/epilogue on "Why China isn't actually a counter example to my whole thesis, tee-hee!!" AKA Chapter 13 literally goes into "well the emperor there had so much power and could unilaterally keep their technology levels down with stupid trade restrictions so that's why Europeans put them through the century of humiliation and eclipsed them!" and other nonsense is straight up massive Sinophobia and very racist.

Diamond makes broad genetic/intelligence claims about whole populations, rankes societies as "advanced/backward" constantly and describes conquest as inevitable

"in mental ability New Guineans are probably genetically superior to Westerners"

"modern "Stone Age" peoples are on the average probably more intelligent"

"some societies seem hopelessly conservative, inward looking, and hostile to change."

Actual quotes from this so called bastion of liberalism

"China’s connectedness eventually became a disadvantage" [because] "a decision by one despot could and repeatedly did halt innovation."

China = monolithic, obedient, centralized, despotic, stagnant; Europe = pluralistic, competitive, innovative.

Diamond turns "Chinese authoritarianism" into a transhistorical condition produced by the land itself. I'm all about the LVT and Georgism and all but this is doing too much service for land.

In other words, the old Orientalist story survives perfectly well after the race science has been supposedly removed from the chassis. Better still, Diamond treats Ming maritime policy, imperial bureaucracy, and Mao’s Cultural Revolution as variations on the same ancient geographical bug, as though two thousand years of Chinese politics were basically the Yangtze River repeatedly pressing the "authoritarianism" button with it's floods!!!