Existing accounts of the origin of human communication assume a pre-existing behavioral system shared among members of a social group. This paper is concerned with the origin of that system; specifically, it explores its characteristics and functionality as well as the circumstances under which it could have appeared. A number of agent-based computer simulations test whether the capacities for arbitrary imitation and pattern completion can lead to a behavioral system that could be co-opted for communication. The results show that arbitrary imitation and pattern completion may indeed generate a population-wide shared behavioral system whose structure reflects the structure of the environment, and therefore could easily have been co-opted for communication. This system may have paved the way for other biological capacities widely believed to be necessary for communication, such as shared intentionality and symbolicity, to co-evolve.