Affective Marking as a Bifurcation Point Between Irony and Deception in Evolved Communicators

How does non-literal language evolve, and what determines whether populations develop cooperative (ironic) versus exploitative (deceptive) communication strategies? We present an artificial life simulation in which populations of neural-network-controlled agents evolve communication strategies in a foraging environment with bidirectional information asymmetry. Both irony and deception involve the same surface mechanism — signal inversion, where an agent uses a signal whose established meaning mismatches the true state of the world. We show that the presence of an affective channel (tone) acts as a bifurcation point: when agents can mark signals with tone, populations evolve intentional irony; when the affective channel is absent, populations evolve deception instead. Across 7 ablation conditions with 20 independent evolutionary runs each (500 generations, 50 agents), we find that: (1) conditions without an affective channel produce zero intentional irony and significantly elevated deception rates (p = 0.013 and p < 0.001 after FDR correction); (2) several conditions with tone show marginally above-baseline tone-inversion coupling, though these effects do not survive multiple-comparison correction, indicating that the coupling is a weak evolutionary tendency rather than a robust strategy; (3) irony occurs more frequently in the listener-to-scout feedback channel (~18%) than in the scout-to-listener commentary channel (~14%), consistent with irony functioning partly as social feedback on deceptive behavior; and (4) the irony-deception balance depends non-linearly on partner retention pressure. These findings identify affective expression as a necessary condition for cooperative non-literal communication, and provide a proof-of-concept framework for studying the evolution of non-literal language.