Following a synthesis of naturalistic and experimental studies of language creation, this paper proposes a theoretical model that describes the process through which human communication systems might arise and evolve. Three key processes are proposed that give rise to effective, efficient and shared human communication systems: (1) motivated signs that directly resemble their meaning facilitate cognitive alignment, improving communication success; (2) behavioral alignment onto an inventory of shared sign-to-meaning mappings bolsters cognitive alignment between interacting partners; (3) sign refinement, through interactive feedback, enhances the efficiency of the evolving communication system. By integrating the findings across a range of diverse studies, the paper proposes a theoretical model of the process through which the earliest human communication systems might have arisen and evolved. Importantly, because the model is not bound to a single modality it can describe the creation of shared sign systems across a range of contexts, informing theories of language creation and evolution.