Genomic Data from an Ancient European Battlefield Indicates On-Going Strong Selection on a Genomic Region Associated with Lactase Persistence Over the Last 3,000 Years

Lactase persistence (LP), the continued expression of lactase into adulthood, is the most strongly selected single gene trait over the last 10,000 years in multiple human populations. It has been posited that the primary allele causing LP among Eurasians, rs4988235*T (Enattah et al. 2008), only rose to appreciable frequencies during the Bronze and Iron Ages (Mathieson et al 2015; Olalde et al. 2018), long after humans started consuming milk from domesticated animals. This rapid rise has been attributed to an influx of peoples from the Pontic-Caspian steppe that began around 5,000 years ago (Allentoft et al. 2015; Furholt et al. 2016). We investigate the spatiotemporal spread of LP through an analysis of 14 warriors from the Tollense Bronze Age battlefield in northern Germany (~3,200 BP); the oldest large-scale conflict site north of the Alps. Genetic data indicate that these individuals represent a single unstructured Central/Northern European population. We complemented these data with genotypes of 18 individuals from the Bronze Age site Mokrin in Serbia (~4,100 to ~3,700 BP) and 37 individuals from eastern Europe and the Pontic-Caspian Steppe region, predating both Bronze Age sites (~5,980 to ~4,250 BP). We infer low LP in all three regions, i.e. in northern Germany, south- eastern, and eastern Europe, suggesting that the surge of rs4988235 in Central and Northern Europe was unlikely caused by Steppe expansions. We estimate a selection coefficient of 0.06, and conclude that the selection was on-going in various parts of Europe over the last 3,000 years.