There are more than 7,000 languages spoken in the world today1. It has been argued that the natural and social environment of languages drives this diversity2,3,4,5,6,7,8,9,10,11,12,13. However, a fundamental question is how strong are environmental pressures, and does neutral drift suffice as a mechanism to explain diversification? We estimate the phylogenetic signals of geographic dimensions, distance to water, climate and population size on more than 6,000 phylogenetic trees of 46 language families. Phylogenetic signals of environmental factors are generally stronger than expected under the null hypothesis of no relationship with the shape of family trees. Importantly, they are also—in most cases—not compatible with neutral drift models of constant-rate change across the family tree branches. Our results suggest that language diversification is driven by further adaptive and non-adaptive pressures. Language diversity cannot be understood without modelling the pressures that physical, ecological and social factors exert on language users in different environments across the globe.
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C.B. and G.J. were funded by the German Research Foundation (DFG FOR 2237; project ‘Words, Bones, Genes, Tools: Tracking Linguistic, Cultural, and Biological Trajectories of the Human Past’) and the ERC Advanced Grant 324246 EVOLAEMP. D.D. was funded by The Netherlands Organisation for Scientific Research VIDI grant 276-70-022 and the European Institutes for Advanced Study Fellowship Program. The funders had no role in study design, data collection and analysis, decision to publish or preparation of the manuscript.
The authors declare no competing interests.
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Supplementary Results 1–4, Supplementary Methods 1–6, Supplementary Note 1
Dediu’s forest data
Maximum likelihood trees data
Environmental variables data
All phylogenetic signals data
Phylogenetic signals for distances to lakes, rivers, and oceans data
Wilcoxon test results by tree set
Wilcoxon results by family
R analysis code files
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Bentz, C., Dediu, D., Verkerk, A. et al. The evolution of language families is shaped by the environment beyond neutral drift. Nat Hum Behav 2, 816–821 (2018). https://doi.org/10.1038/s41562-018-0457-6