Computational phylogenetics reveal the history of sign languages

Sign languages are naturally occurring languages. As such, their emergence
and spread reflect the histories of their communities. However,
limitations in historical recordkeeping and linguistic documentation have
hindered diachronic analysis of sign languages. Here, we use computational
phylogenetic methods to study family structure among 19 sign languages
from deaf communities worldwide. We use phonologically coded lexical data
from contemporary languages to infer relatedness, and suggest these
methods can help study regular form changes in sign languages. The
inferred trees are consistent in key respects with known historical
information, but challenge certain assumed groupings and surpass analyses
made available by traditional methods. Moreover, the phylogenetic
inferences are not reducible to geographic distribution, but do affirm the
importance of geopolitical forces in the histories of human languages.