Writing does not Impact the Evolution of Syntax

The acquisition of writing has a lasting effect on how languages are processed in the brain, raising the possibility that it also affects how they are used and evolve over time. A popular hypothesis is that writing specifically leads to increased use and evolution of complex hierarchical structures in language. While most case studies on individual languages have supported this, it remains unclear whether results scale to larger and more diverse sets of languages. Here we test the prediction for language use by modeling hierarchy depth and sentence length in Universal Dependencies corpora from 30 languages, and the prediction for language evolution by modeling the phylogenetic dynamics of structural asymmetry in clause combinations of 59 languages from three families. We found no effect of writing in either analysis. Hierarchy depth and sentence length do not demonstrably differ between spoken and written use of language, and the introduction of writing had no discernible effect on the evolution of clause combining in grammar. There is weak evidence for a decrease in variance after the introduction of writing in one family, possibly reflecting the impact of increased normativity. In conclusion, our findings challenge popular beliefs about hierarchy and suggest that the evolution of syntax is more driven by culturally variable ideas about style in linguistic expression than by the evolution of writing.