Parental relatedness through time revealed by runs of homozygosity in ancient DNA

Little is known about how human parental relatedness varied across ancient populations. Runs of homozygosity (ROH) in the offspring's genome can give clues. Here, the authors present a method to identify ROH in ancient genomes and infer low rates of close kin unions across most ancient populations. Parental relatedness of present-day humans varies substantially across the globe, but little is known about the past. Here we analyze ancient DNA, leveraging that parental relatedness leaves genomic traces in the form of runs of homozygosity. We present an approach to identify such runs in low-coverage ancient DNA data aided by haplotype information from a modern phased reference panel. Simulation and experiments show that this method robustly detects runs of homozygosity longer than 4 centimorgan for ancient individuals with at least 0.3 x coverage. Analyzing genomic data from 1,785 ancient humans who lived in the last 45,000 years, we detect low rates of first cousin or closer unions across most ancient populations. Moreover, we find a marked decay in background parental relatedness co-occurring with or shortly after the advent of sedentary agriculture. We observe this signal, likely linked to increasing local population sizes, across several geographic transects worldwide.

Automated summary

The study reveals low rates of close kin unions in most ancient populations through analysis of ancient DNA data, as well as a marked decay in background parental relatedness coinciding with or shortly after the advent of sedentary agriculture. This signal, likely linked to increasing local population sizes, is observed across several geographic transects worldwide.