Ternary, gradually changing reputation system found to sustain cooperation in indirect reciprocity
Rissho University
[Background and Purpose]
A research team led by Hitoshi Yamamoto (Rissho Univ. JAPAN) has unveiled new insights into how humans build and update reputations in cooperative social interactions. Human societies have achieved remarkable levels of cooperation, facilitated mainly by mechanisms of indirect reciprocity, where reputation and social norms play crucial roles. While theoretical models have proposed complex, multi-layered systems for how reputation information sustains cooperation, experimental studies often rely on oversimplified binary categorizations. This research aimed to bridge this gap by investigating the type of information and level of granularity required to define and maintain reputation-based cooperation in real-world contexts. The study's results appeared in PLOS One on August 8, 2025.
[Key Findings]
Through scenario-based experiments combined with mathematical modeling, the study revealed that reputations are best understood not as binary (good/bad) but as ternary (good/neutral/bad) categories that change gradually based on cooperative or defective behaviors. Notably, defecting against individuals with bad reputations did not degrade the defector's reputation, suggesting that justified defection is viewed neutrally rather than positively. Theoretical analyses demonstrated that under certain conditions, a tolerant action rule—cooperating with those of good or neutral reputation and defecting only against those with bad reputations—becomes dominant and stabilizes cooperation.
[Significance]
These findings challenge traditional views of abrupt, binary shifts in reputation and highlight the importance of gradual, nuanced updates that mirror real-world social dynamics. The research offers a more realistic model of how social norms evolve and sustain cooperation, providing empirical evidence to support the theoretical claim that multi-valued reputation systems are crucial for maintaining stable cooperation in large-scale human societies.
[Future Directions]
Lead author Yamamoto notes that future research will expand on these findings by examining cross-cultural differences in reputation evaluations and exploring how introducing greater reputation granularity may further influence cooperative behavior. Understanding these dynamics could inform the design of effective mechanisms for sustaining cooperation in digital platforms and globalized communities.
Journal
PLOS One
Article Title
Gradual reputation dynamics evolve and sustain cooperation in indirect reciprocity
Article Publication Date
18-Aug-2025
Blending direct and indirect reciprocity: Tolerant integrated reciprocity found to sustain cooperation in noisy environments
Rissho University
[Key Findings]
A research team led by Professor Hitoshi Yamamoto (Rissho University, Japan) has developed a new model that integrates direct and indirect reciprocity, the two core mechanisms underpinning human cooperation. Unlike previous models that treat these processes separately, this study proposes a tolerant integrated reciprocity strategy that draws upon both personal experience and social reputation. The study's results appeared in Scientific Reports on August 7, 2025.
Through agent-based simulations, the study demonstrates that this integrated approach, particularly when combined with a social norm known as “Standing”, can maintain high levels of cooperation even in noisy environments where errors in judgement and communication frequently arise.
[Background and Significance]
While direct reciprocity (“I help you because you helped me”) and indirect reciprocity (“I help you because you helped someone else”) have traditionally been studied in isolation, real-world decision-making often involves a flexible combination of both.
This research reveals that incorporating tolerance, such as choosing to cooperate even when reputational cues are unreliable, can significantly improve cooperation outcomes. These findings have broad implications for designing resilient cooperation systems in the digital age, where noise and misinformation are common.
Lead author Yamamoto notes that “Human cooperation is a delicate balance of fairness and forgiveness. Our study shows that people do not rely solely on reputation; they also consider how others have treated them directly. This dual-track strategy helps maintain cooperation in uncertain environments and may offer insights for designing better trust systems in online platforms and beyond.”
Journal
Scientific Reports
Article Title
Tolerant integrated reciprocity sustains cooperation in a noisy environment
Article Publication Date
17-Aug-2025
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