The Dutch are culturally very modern and rather cosmopolitan, despite having a small country (half the size of South Carolina in area) as a homeland. Yet, the genes of Dutch people still strongly predict where someone is from within this country on a North-South axis.
We studied fine-grained population genetic structure and demographic change across the Netherlands using genome-wide single nucleotide polymorphism data (1,626 individuals) with associated geography (1,422 individuals). We applied ChromoPainter/fineSTRUCTURE, identifying 40 haplotypic clusters exhibiting strong north/south variation and fine-scale differentiation within provinces. Clustering is tied to country-wide ancestry gradients from neighbouring lands and to locally restricted gene flow across major Dutch rivers. Despite superexponential population growth, north-south structure is temporally stable, with west-east differentiation more transient, potentially influenced by migrations during the middle ages. Within Dutch and international data, GWAS incorporating fine-grained haplotypic covariates are less confounded than standard methods.
Ross P. Byre, et al., "Dutch population structure across space, time and GWAS design" bioRxiv (January 2, 2020) doi: https://doi.org/10.1101/2020.01.01.892513