The evolution of language families is shaped by the environment beyond neutral drift

Abstract

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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Fig. 1: Density distributions of phylogenetic signals for K and λ, and violin plots with distributions per environmental factor.
Fig. 2: Environmental factors reflected on family trees.
Fig. 3: Percentages of subsets in line with evolutionary hypotheses.

Data availability

Data availability is detailed in Supplementary Methods 1. Individual data files are described in Supplementary Data 17 in the Guide to the Supplementary Information.

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Acknowledgements

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.

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C.B. was responsible for project inception, statistical and phylogenetic analyses, and writing of the paper. D.D., A.V. and G.J. contributed data, phylogenetic analyses and writing.

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Correspondence to Christian Bentz.

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Supplementary information

Supplementary Information

Supplementary Results 1–4, Supplementary Methods 1–6, Supplementary Note 1

Reporting Summary

SI Guide

Supplementary Data set 1

Dediu’s forest data

Supplementary Data Set 2

Maximum likelihood trees data

Supplementary Data Set 3

Environmental variables data

Supplementary Data Set 4

All phylogenetic signals data

Supplementary Data Set 5

Phylogenetic signals for distances to lakes, rivers, and oceans data

Supplementary Data Set 6

Wilcoxon test results by tree set

Supplementary Data Set 7

Wilcoxon results by family

R code file

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

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