The theory of evolution is “unreasonably effective” (in Wigner’s terms) in that it seems to apply to both biological evolution and cultural change -- domains that might seem completely unrelated. Nowhere is this parallelism clearer than in the domain of language, where there is both an evolved biological basis for language and processes of cultural evolution that lie behind the diversification of languages. Language is clearly a bio-cultural hybrid -- we are biologically equipped for language in general, but inherit the specific cultural form of the languages in which we are socialized. This symposium explores the genetic foundations of language, the phylogenetic patterns of cultural diversification in language, and the ongoing interplay between biological and cultural evolution. Individual papers will address the relation between linguistic ability, brain, and genes; the biological basis for communicative interaction; the phylogenetic patterns in language diversification both in form and content; the effects of population genetics on language diversification; and the case of village sign languages: the interplay between genetics and language type. The papers suggest that one reason that evolutionary theory applies so well to both biological and cultural phenomena is that the two are intertwined and in ongoing interaction.