Trust Before Payoff A Dual-Gate Model of Cooperation

AbstractStandard models treat the probability of cooperation as an exogenous parameter. In practice, individuals construct this probability from subjective information about the partner. I propose a dual-gate model in which cooperation requires a relational prior—the Partner Suitability Index (H)—to exceed a threshold before any payoff evaluation occurs. H integrates four subjective dimensions: perceived identity overlap (G), recalled cooperative history (M), affective evaluation (A), and estimated competence (C). H is unbounded above; surplus suitability progressively suppresses the demand for payoff. At sufficiently high H, the payoff threshold becomes negative: the individual willingly accepts a net personal cost to benefit the partner, entering the partner's fitness equation. The framework is anchored in Hamilton's rule, social identity theory, reciprocal altruism, and affective neuroscience.Keywords: cooperation; dual-gate model; partner suitability; Hamilton's rule; social identity; reciprocal altruism