When Environment Becomes Biology: The Dissolving Diamond Dichotomy

Diamond's famous thesis rests on a clean dichotomy: history diverged because of environments, not because of biological differences among peoples themselves. The rhetorical force of Guns, Germs, and Steel depends on these being separable categories — geography on one side, genes on the other, with geography doing all the causal work.

The ancient DNA study quietly dissolves that separation. If hundreds of alleles underwent strong directional selection in West Eurasia within just the past ten millennia — precisely the window Diamond's argument covers — then environments didn't merely substitute for biology as an explanation. Environments were actively writing themselves into biology, shifting predicted complex traits by a full standard deviation. Agriculture, dense settlement, novel pathogens, new diets: these are exactly the environmental differences Diamond catalogues, and they are plausibly the selective pressures the genomic data records.

This doesn't vindicate the racialist arguments Diamond was writing against — if anything, it inverts them. The causal arrow still starts with geography: whatever biological change occurred was downstream of environmental circumstance, not an independent prior cause of civilizational divergence. Diamond could absorb the finding by amending his claim to "not because of pre-existing biological differences." But the amended claim is weaker and stranger than the original, because it concedes that ten thousand years is enough time for environments to produce biological differences, which then become part of the historical process themselves. The tidy one-way street becomes a feedback loop.

The study's authors offer a crucial hedge that keeps this from becoming a just-so story: the trait shifts are measured against polygenic predictors calibrated in modern industrialized societies, and "it remains unclear how these relate to phenotypes that were adaptive in the past." A decrease in predicted schizophrenia risk or an increase in a cognitive-performance score tells us selection acted on these alleles, not that it acted on those traits as we understand them. So the honest synthesis is unsettling in both directions: Diamond's dichotomy is too clean, but anyone rushing to fill the gap with confident claims about what selection was "for" is outrunning the evidence.