David Reich – Bronze Age shock, the Neanderthal puzzle, & the sudden spread of farming

Ancient DNA reveals recent selection surge and Neanderthal mysteries

1. A.A new high-sample ancient-DNA analysis finds thousands of genomic sites likely under directional selection over the last ~10,000–18,000 years, overturning the view that recent human selection was largely quiescent.
2. B.Selection signals are disproportionately enriched in immune and metabolic traits, with the strongest intensification often occurring in the Bronze Age (roughly 5,000–2,000 years ago), suggesting a major lifestyle/disease ecology shock tied to high density, pastoralism, and pathogen exchange.
3. C.Behavioral/cognitive traits show weaker single-locus signals because they are highly polygenic, but polygenic-score analyses still suggest systematic shifts (including a notable Bronze Age peak for variants associated with schooling/IQ proxies), alongside important caveats about what these proxies mean.
4. D.Reich argues population size is rarely the limiting factor for these observed selection rates; instead, the key constraints are time and the ability to separate selection from migration-driven allele-frequency swings.
5. E.The episode explores big-picture mysteries: why farming arose only after Holocene climate stability despite long-standing human cognitive capacity, and a “Neanderthal puzzle” where mtDNA/Y-chromosome patterns and shared culture hint at a more complex relationship than the standard Neanderthal–Denisovan sister model suggests.