Which account of language origin is more plausible: that language emerged primarily through gestures, or through vocalisations? I present a model of sign creation and change, explaining how people bootstrap communication systems in the absence of a shared language. I test this model over 8 experiments; in each, modern human participants attempted to communicate meanings to a partner through gestures or non-lexical vocalizations. I examined adult communication (experiments 1-3), child communication (experiments 4, 5) and communication with varying task difficulty (experiments 6-8). Across all experiments, my results support an account of language creation in which gesture played an integral role.