A BEAST 2 package to infer contact in language trees

Phylogenetic trees show how languages have diversified over time, but ignore a central aspect of language evolution — contact. Using contacTrees we can infer a phylogenetic tree with contact events, where one language borrowed linguistic traits from another one.

When two languages share certain traits this may be due to inheritance from a common ancestor. Phylogenetic methods use this fact to infer the ancestral relationships — or phylogenetic tree — of a language family. 

Yet, languages can also adapt traits from other languages they are in contact with. This is called linguistic borrowing and is ignored by current phylogenetic methods.

contacTrees combines the two processes: it infers a phylogenetic tree, reflecting the ancestry of languages, and contact edges, representing events where one language borrowed traits from another one. This gives us a new way to study language contact and makes phylogenetic inference resilient to borrowing in the data.

contacTrees is an open source BEAST 2 package. Installation guidelines, usage instructions and source code can be found on github.