Researchers working with artificial life software have developed a simulation based on a case study of vervet monkeys that demonstrates the emergence of symbol-based communication among the creatures. Their research is described in a recent paper titled, The Emergence of Symbol-Based Communication in a Complex System of Artificial Creatures (PDF format). In the simulation, cooperative interactions that included symbol-based communication raised the fitness of individuals in the face of predatory events. The emergence of self-organizing symbol-based communication in this type of scenario offers interesting evidence of the origin of language in the anti-predatory alarm calls of animals. This ties in nicely with previous research we've reported on done at the Sony Computer Science Lab on the evolution of language from self-organizating speech sounds.