Human language is a culturally evolving system.

It is well accepted that languages change rapidly in a process of cultural evolution. But some animal communication systems, in particular bird song, also exhibit cultural change. So where exactly is the difference? This article argues that the main selectionist pressure on human languages is not biological-that is, related to survival and fecundity-but instead is linked to producing enough expressive power for the needs of the community, maximizing communicative success, and reducing cognitive effort. The key question to be answered by an "evolutionary linguistics" approach to language is, What are the causal mechanisms sustaining an evolutionary dynamic based on these selection criteria? In other words, what cognitive mechanisms and social interaction patterns are needed, and how do they allow a language to emerge and remain shared, despite profound variation and never-ending change?