Assessing the impact of 20th century internal migrations on the genetic structure of Estonia

Spatial genetic structure observed in many human populations is in large part attributed to past demographic events and isolation by distance. However, how intensifying migration affects this structure remains understudied. Here we harness a sample of more than 180 thousand individuals to explore the genetic correlates and consequences of contemporary migrations in Estonia. While we show that migration smoothens the genome-wide genetic structure, it intensifies inter-regional differences in polygenic scores (PGS) for certain traits, derived both from population as well as within-sibship studies. The strongest effect is observed for educational attainment which is consistent with previous observations in the UK and suggests this to be a general pattern. We explore those regional differences in PGS in terms of the driving forces behind them and from a temporal perspective, and suggest urbanisation as a major driver for this pattern in Estonia from at least the first half of the 20th century.