GENETICS × HEALTH

Lactase Persistence

~6,000 years ago

Neolithic · Neolithic · Holocene · Northgrippian

The gene variant that lets most European adults digest milk first appears in ancient genomes about 6,000 years ago.

Lactase persistence designates the maintenance into adulthood of production of the enzyme allowing the digestion of lactose, a character most mammals lose after weaning. The variant responsible in European populations, located upstream of the LCT gene and designated -13910*T, appears in ancient genomes about 6,000 years ago and ranks among the most strongly selected human variants of the last ten millennia. The nature of the advantage conferred nevertheless remains debated: milking and fermentation are attested in Europe several millennia before the variant spreads, and herding populations lacking persistence today consume dairy products without difficulty.

Why it matters

The case documents a modification of the human genome consequent upon a cultural practice, herding preceding selection of the variant. The mechanism most compatible with the data does not involve ordinary milk consumption but situations of crisis: in a non-persistent individual, lactose causes diarrhoea, of no gravity in normal times but capable of producing fatal dehydration during famine or alongside infection. Models based on famine and pathogen exposure reproduce the observed trajectory better than those based on dietary use alone.

Dating & uncertaintyDisputed

The European variant is attested in Ukraine 5,960 years ago and spreads widely with the steppe migrations less than 4,000 years ago; an earlier model placed it under selection among dairying populations between the central Balkans and central Europe about 7,500 years ago. The question of the selective factors remains open.

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