The co-evolution of costly markers and cooperation in social dilemmas

Abstract

Costly cooperation and the evolution of costly signals are both difficult to reconcile with simple fitness maximization, yet both are common in biological and social systems. We study a model in which agents emit costly signals and condition their actions on the signals they observe. The signals are arbitrary, non-costless markers: they need not reveal hidden biological quality, and their value can arise through the heritable response rules associated with them. Across the Prisoner’s Dilemma (PD), Snowdrift (SD), and Stag Hunt (SH) games, we ask when this coevolutionary process can sustain cooperation and how it changes across well-mixed populations, spatial lattices, and fluctuating strategic environments. The simulations show that signals are selected less by their raw production costs than by the cooperative responses they currently elicit. No-signal baseline controls show that the signal response layer is essential for maintaining cooperation in the PD and under the SD update rule studied here, whereas SH already favors cooperative coordination. In well-mixed populations, the mechanism sustains partial cooperation in PD and SD and drives near-complete cooperation in SH. On lattices, cooperation is strengthened further by local assortment. An independence-based mean-field analysis reproduces the qualitative SD and SH regimes but not partial cooperation in the PD. A separately parameterized, phenomenological rarity correction is sufficient to produce a partially cooperative PD regime, illustrating one possible role for omitted frequency-dependent correlations without identifying them uniquely. Our results therefore delineate a class of settings in which arbitrary costly signals persist because they transiently organize cooperative responses and thereby reshape the effective strategic environment.