A computational analysis has highlighted the poorly understood relationships and elusive histories of modern sign languages worldwide, revealing two major sign language families shaped by geopolitical forces and relevant signing communities. The findings show that the computational methods applied – which have been useful in understanding spoken languages – can be extended to the study of sign languages; as such, they offer promise for addressing the disparities in our understanding of other marginalized and diverse languages and communities. Language – a defining feature of human existence – is constantly changing and evolving. Throughout the world and across time, variations in language often reflect the histories of the communities that share them. Recent advances in computational phylogenetics have been used to detect more nuanced evolutionary relationships among the vocabularies and grammatical properties of different spoken language groups, revealing otherwise obscured histories. Like spoken languages, sign languages are naturally occurring and used worldwide. However, as is often the case for marginalized, understudied languages, the evolution and of sign languages within the communities that use them is far less understood compared to their spoken alternatives. One of the main challenges in this space is the dynamic iconicity of the fluid visual-gestural movements upon which sign languages are built. As a result, linguistic documentation is often insufficiently limited to static images or narrative descriptions.
To address this gap, Natasha Abner and colleagues applied computational phylogenetic methods to study family structure among 19 contemporary sign languages used worldwide. Abner et al. gathered video dictionary entries of core vocabulary from each sign language and developed a database of coded sign forms. Each sign was individually coded based on basic phonetic parameters of the sign form. Phylogenetic analysis of this dataset revealed two independent sign language families – European and Asian – as well as an articulated family tree for each. The authors discovered no evidence of long-term contact between European and Asian sign languages. Notably, however, the findings demonstrated a closer relationship between the Western European sign languages and British and New Zealand sign languages than has been previously assumed. Moreover, Abner et al. show that their Western European sign language family tree reflects the broad influence of French sign language and the geopolitical history of nations that established deaf education schools during the 18th century. Two distinct subfamilies of Asian sign languages were also identified.
