Gradient in grammatical structure of indigenous languages reflects pathway of human expansion in the Americas.

The settlement of the Americas is one of the major episodes of prehistoric human dispersal, and involved multiple temporally and geographically uneven demographic events that continued into the Holocene. Here we suggest the possibility that these complex dynamics are reflected in the spatial structure of Indigenous linguistic diversity. On the basis of newly collated data, we find more pronounced spatial structure in linguistic diversity in North America than in South America after known genealogy and language contact are accounted for. Furthermore, we report a continent-wide gradient in aspects of sound systems and grammatical structure that mirrors early north-south dispersal paths, and that is not explained by local language contact and known phylogenetic relationships.