In historical linguistics, the wave model or wave theory (German Wellentheorie) is a model of language change in which a new language feature (innovation) or a new combination of language features spreads from a central region of origin in continuously weakening concentric circles, similar to the waves created when a stone is thrown into a body of water. The theory was intended as a substitute for the tree model, which did not seem to be able to explain the existence of some characters, especially in the Germanic languages, by descent from a proto-language. At its most ambitious, it is a wholesale replacement for the tree model of languages. During the 20th century, the wave model has had little acceptance as a model for language change overall, except for certain cases, such as the study of dialect continua and areal phenomena; it has recently gained more popularity among historical linguists, due to the shortcomings of the Tree model.