Origins of raw milk consumption in the Iberian Peninsula and Portuguese territory: archaeogenetics and zooarchaeology

In Europe, lactose tolerance after weaning (lactase persistence – LP) is determined by a single mutation in the MCM6 gene. The timing and mode of the emergence of raw milk consumption in Portuguese territory have not been addressed, despite its significance in Portuguese subsistence and culinary tradition. To identify the earliest instance of the LP mutation, we examined this locus in ancient DNA (aDNA) data from Iberian individuals spanning from the Palaeolithic to the Modern Age, available in the Allen Ancient DNA Resource database. Additionally, we reviewed zooarchaeological data on domesticated milk-producing species from bibliographic sources. In Iberia, the earliest occurrence of the LP mutation dates to the Early Bronze Age. The individual also carried the Y-chromosome Haplogroup R1b, typically associated with the hypothesised Yamnaya movement during this period. In Portugal, the first individual with LP dates to the Roman Period. Zooarchaeological data suggest that milk was consumed in small quantities in Portugal until the Roman Period. Milk production increased more significantly during the Middle Ages, but its impact on LP remains to be determined.