GENETICS × HEALTH

Learning to Drink Milk

~6,000 years ago

Neolithic · Neolithic · Holocene · Northgrippian

Most mammals lose the ability to digest milk after weaning; many humans no longer do. The European mutation that keeps lactase switched on appears in ancient genomes about 6,000 years ago and became one of the most strongly selected human variants of the last ten millennia. Yet Europeans had milked and fermented for thousands of years before it spread, and lactose-intolerant herders manage fine today, so what exactly the gene was selected for is genuinely disputed.

Why it matters

This is the textbook case of culture rewriting biology: herds first, gene second. The surprise is in the mechanism, since milk-drinking alone barely explains the selection; famine and disease, turning mild indigestion into a killer, fit the data better. Half the fiche's lesson is scientific humility, as the tidy story taught for decades is being reargued with ancient DNA.

Dating & uncertaintyDisputed

The European variant is first seen about 5,960 years ago in Ukraine and spreads widely with the steppe migrations after 4,000 years ago; modelling once placed its selection among Balkan dairy farmers around 7,500 years ago. Why it was favoured is the live dispute: milk use alone explains the trajectory poorly, and famine and pathogen exposure are now proposed as the real drivers.

Sources

1. Evershed et al. (2022), Nature · Dairying, diseases and the evolution of lactase persistence in Europedoi:10.1038/s41586-022-05010-7
2. Ségurel et al. (2020), PLoS Biology · Why and when was lactase persistence selected for? Insights from Central Asian herders and ancient DNAdoi:10.1371/journal.pbio.3000742
3. Itan et al. (2009), PLoS Computational Biology · The origins of lactase persistence in Europedoi:10.1371/journal.pcbi.1000491

Our species’ history as one day

23:32:3427 min 26 s before midnight

if the 315,000 years of Homo sapiens were compressed into a single day