Along with complexity, the extent of the variability of human language across social groups is unprecedented in the animal kingdom, and we need to understand how this is possible. An underdetermined innate basis is plausible, but there is no consensus about what it is (other than vocal learning and the vocal apparatus), or how it would make it possible to learn varied languages. An alternative, and potentially complementary, explanation suggests that there is a set of communicative instincts and motivations that together make it possible for the infant to bootstrap into the local language, whatever it may be. Some evidence for this is as follows. First, the organization of informal interactive human communication – the core niche for language use – looks much less variable than languages. Thus all language users in this niche take rapid turns at talking even though the speed of this is highly demanding. Similarly, all users avail themselves of the same mechanisms for repairing miscommunication, and use the same restricted system for building coherent dialogues. Second, long before infants have any linguistic knowledge, they take part in ‘proto-conversations’ that exhibit these same universal organizations. Third, where normal spoken language is not accessible to individuals (as when they are profoundly deaf), they still share the same communicative infrastructure. Finally, there are some signs of phylogenetic parallels in other primates. If this is correct, Darwin’s characterization of language as “an instinct to acquire an art” may have its root in communicative instincts as much as specific instincts about language structure