"Human parental relatedness through time: Detecting runs of homozygosity in ancient DNA"


At present day, human parental relatedness varies substantially across the globe, but little is known about the past. Here we use ancient DNA to provide new insights, leveraging that parental relatedness leaves traces in the offspring’s genome in the form of runs of homozygosity. We present a method to identify such runs in low-coverage ancient DNA data using linkage information from a reference panel of modern haplotypes. As a result, the method facilitates analysis of a much larger fraction of the global ancient DNA record than previously possible. Simulation and experiments show that this new method has power to detect runs of homozygosity longer than 4 centimorgan for ancient individuals with at least 0.3× coverage. We used this new method to analyze sequence data from 1,785 humans from the last 45,000 years. Generally, we detect very low rates of first cousin or closer unions across most ancient populations. Moreover, our results evidence a substantial impact of the adoption of agricultural lifestyles: 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 regions worldwide."

Basically, that boils down to the fact that hunter-gatherers practiced more first cousin marriage (and closer) than farmers, but from the paper itself it seems that much more recently there was an increase in inbreeding, and that it was more intense and continues to this day in certain parts of the world.

Very bad idea, imho.

Razib Khan opined:

"The major thing to note is that the estimates suggest cousin-marriage was far less common in the prehistoric and historic past than it is in some modern societies. In particular, it is far less common than it is today in the Islamic world and in India. "