This paper aims to test the hypothesis that language is a complex tool system by drawing an analogy with primate cognition in great apes. Data show that wild chimpanzees manifest considerable cross-group variation in one domain of tool use such as nut-cracking, thus indicating that cultural development affects primate cognition. This correlates with cross-cultural patterns of variation in the grammatical encoding of reciprocity (e.g., “Mary and John love each other”) in natural languages. Therefore, the tool use analogy can explain cognitive foundations and cultural development in linguistic and prelinguistic behavior without having to resort to innate universals.