Fig. 3: Identity by Descent (IBD) segments shared among individuals from DSKC, figure-shaped and Slab graves.

A The violin plot comparing the sum of IBD segments shared between individuals (1) within the geographic proximity group and (2) within the mortuary proximity group. The geographic proximity group includes pairs from different mortuary traditions (DSKC and figure-shaped) found within 200 km in central Mongolia. The mortuary proximity group includes pairs from the same tradition but from sites >200 km apart, with one individual from central Mongolia. The sum of each pair is shown as colored symbols. The two-sided p-value for the Wilcoxon rank-sum test is shown at the top of the plot. B Three pairs sharing over 100 cM of IBD plotted against the simulated IBD of genetically related pairs. The x-axis represents the sum of IBD segments of at least 12 cM, while the y-axis shows the number of these segments. The IBD segments of 14 familial relationships, with 100 replicates simulated using Ped-sim, are represented by distinct colors. Newly analyzed pairs are represented by black triangles, with three labeled pairs sharing over 100 cM of IBD. C The distribution of IBD enrichments between figure-shaped and Slab Grave individuals, generated through permutations. We tested the cultural diffusion model for the Slab Grave expansion in central Mongolia by examining the IBD enrichment shared between figure-shaped individuals from central Mongolia (Fc) and Slab Grave individuals from central Mongolia (Sc). To assess this enrichment, we calculated the ratio of average IBD shared between Fc and Sc (FcSc) to that shared between figure-shaped individuals from eastern Mongolia (Fe) and Sc (FeSc). Each ratio was then normalized using Slab Grave individuals from outside central Mongolia (FcSo and FeSo, respectively) to account for the background IBD level of Sc. A significantly high value of (FcSc/FcSo)/(FeSc/FeSo) would suggest genetic continuity in central Mongolia over time, supporting a cultural diffusion model for the Slab Grave expansion. The ratio was calculated for 10,000 permutations, and the distribution is shown in the figure, with the red vertical line marking the observed value. Source data are available in Supplementary Data 7, 9, and 13, as well as at https://zenodo.org/records/16743201¹⁰³.