The evolution of functionally referential meaning in a structured world.

Animal communication systems serve to transfer both motivational information--about the intentions or emotional state of the signaler--and referential information--about external objects. Although most animal calls seem to deal primarily with motivational information, those with a substantial referential component are particularly interesting because they invite comparison with words in human language. We present a game-theoretic model of the evolution of communication in a "structured world", where some situations may be more similar to one another than others, and therefore require similar responses. We find that breaking the symmetry in this way creates the possibility for a diverse array of evolutionarily stable communication systems. When the number of signals is limited, as in alarm calling, the system tends to evolve to group together situations which require similar responses. We use this observation to make some predictions about the situations in which primarily motivational or referential communication systems will evolve.