A great variety of organisms communicate in a great variety of different ways, from the quorum sensing of bacteria to the harmonies of songbirds. Human communication is, nevertheless, especially and manifestly distinctive, particularly with regards to its expressive range, and it is hard to overstate the central role that communication plays in human social and cultural life. It is commonly assumed, across many disciplines, that what makes human communication so richly expressive is the generative power of natural language. This assumption in turn shapes the research agenda in several areas, including psycholinguistics, semantics, language evolution, philosophy of language, comparative cognition, and others. I will present and argue for an alternative explanation grounded in cognitive pragmatics. Specifically, I will argue that what causes human communication to be so expressively rich is its ostensive character, by which speakers make manifest their communicative intentions, and where audience interpretation is guided by presumptions of relevance. Lexicons, grammars, and the other parts of natural languages are, on this view, structured collections of culturally evolved tools, the proper function of which is to exploit the various opportunities made possible by ostensive communication. I will outline the ecological conditions under which this means of expression can emerge and/or evolve.