The analysis of admixture considering a structured ancestral Native American population also suggests that a stronger regional ancestry is present in the smaller urban centers sampled. The variance of the estimated Native ancestry components is negatively correlated with the logarithm of population size (Table S1), both in the linguistic-based analysis (Figure 5, ρ = −0.611, P<0.05) and in the population-based analysis (Figure 6, ρ = −0.661, P<0.05). The more heterogeneous Native American ancestry of larger urban agglomerations is consistent with them having attracted immigrants from relatively distant areas, thus potentially tracing their ancestry to various, differentiated Native groups. By contrast, smaller urban centers appear to trace their ancestry to fairly defined Native groups, with subsequent maintenance of greater isolation than larger agglomerations. This genetic pattern agrees with demographic data showing that the expansion of major cities in Latin America has often been driven by regional immigration rather than by internal growth[41].
