Empires, alliances and cultural exchanges formed connections between deaf communities around the world that can be traced with a new method for studying sign languages.

Why it matters: There are more than 300 sign languages but they and the communities that use them have been "marginalized, underdocumented and understudied," leaving a gap in understanding about human communication, the researchers write in the journal Science.

What they did: Computational tools have revealed how different spoken languages are related, helping to trace the histories of the people who speak them.

• Applying those same tools to sign languages has been more difficult because the historical records about sign languages are thin and the languages are documented as static images even though they are practiced using fluid movements of gestures, the researchers write.
• A team led by Natasha Abner, a professor of linguistics at the University of Michigan, analyzed the relationship between 19 sign languages by coding different parameters of a sign's form for core vocabulary, including handedness (one- or two-handed), the number of selected fingers, and the location of the signing space in relation to the body and movement.

What they found: The novel computational analysis revealed two separate sign language families — European and Asian — that don't appear to have had any long-term contact between them.

• They found Western European sign languages and British and New Zealand sign languages are more closely related than previously thought.
• They also described a family of Western European sign languages broadly influenced by French sign language, supporting previous findings. "During the rapid expansion of deaf education in the 18th and 19th centuries, many schools and teachers had connections to France and the French educational system," they write.
• A cluster of Czech, Austrian and German sign languages shaped by exchanges in the Prussian kingdom and Austro-Hungarian Empire "resist a purely geographic explanation and affirm that languages reflect the histories of the lands and peoples using them."
• They also detected two subfamilies of Asian sign languages.

The big picture: The methods "offer promise in overcoming the disparities in our understanding of the histories of diverse languages and communities," the team writes.