The bacteria that shaped history: Yersinia pestis – David Reich

David Reich argues Yersinia pestis may have killed a quarter to half of Western Eurasians over a 5,000-year span, potentially triggering Europe’s Bronze Age population replacement.

• Ancient DNA shows Yersinia pestis in 5–10% of randomly sampled deaths in Western Eurasia 4,000–5,000 years ago, implying far higher true infection rates.
• The strain lacked the flea-rat transmission plasmid, suggesting pneumonic (airborne) spread, not bubonic plague.
• ~4,500 years ago, 90% of Britain’s farming population was replaced within ~100 years by steppe migrants; the same pattern appears across all of Europe.
• Reich’s hypothesis: plague-driven population collapse created conditions for steppe people to displace denser farming societies, mirroring European displacement of New World populations.
• A recent Scandinavian paper found well over 10% of farmers buried in 5,000-year-old tombs positive for Yersinia pestis—higher than earlier estimates.
• Yersinia pestis is also documented in the Plague of Justinian, linked to the fall of the Roman Empire, and the medieval Black Death.
• Economist Robert Allen’s theory: the medieval plague drove wage inflation in Britain, making labor expensive enough to incentivize mechanization and spark the Industrial Revolution.

2024-08-26 · Watch on YouTube