Fortune Favours the Bold: An Agent-Based Model Reveals Adaptive Advantages of Overconfidence in War

Overconfidence has long been considered a cause of war. Like other decision-making biases, overconfidence seems detrimental because it increases the frequency and costs of fighting. However, evolutionary biologists have proposed that overconfidence may also confer adaptive advantages: increasing ambition, resolve, persistence, bluffing opponents, and winning net payoffs from risky opportunities despite occasional failures. We report the results of an agent-based model of inter-state conflict, which allows us to evaluate the performance of different strategies in competition with each other. Counter-intuitively, we find that overconfident states predominate in the population at the expense of unbiased or underconfident states. Overconfident states win because: (1) they are more likely to accumulate resources from frequent attempts at conquest; (2) they are more likely to gang up on weak states, forcing victims to split their defences; and (3) when the decision threshold for attacking requires an overwhelming asymmetry of power, unbiased and underconfident states shirk many conflicts they are actually likely to win. These “adaptive advantages” of overconfidence may, via selection effects, learning, or evolved psychology, have spread and become entrenched among modern states, organizations and decision-makers. This would help to explain the frequent association of overconfidence and war, even if it no longer brings benefits today.

过度自信长期以来被视作战争的诱因之一。与其他决策偏差类似，过度自信看似具有破坏性——因其会提升武装冲突的发生频率与代价。然而，进化生物学家提出，过度自信或许也能带来适应性优势：提升抱负、强化决心与韧性，通过虚张声势迷惑对手，并从风险机遇中获取净收益，即便偶尔会遭遇失败。本研究报告了一项国家间冲突的基于智能体的模型（agent-based model）的研究结果，该模型可用于评估不同策略在相互竞争中的表现。反直觉的是，我们发现过度自信的国家会以牺牲实力评估客观无偏的国家与自信不足的国家为代价，在种群中占据主导地位。过度自信的国家之所以获胜，原因在于：其一，它们更有可能通过频繁的征服尝试积累资源；其二，它们更倾向于联合攻击弱国，迫使防御方分散战力；其三，当发动攻击的决策阈值要求压倒性的力量优势时，实力评估客观无偏与自信不足的国家会回避诸多本可获胜的冲突。这些过度自信的“适应性优势”，或许会通过选择效应、学习过程或进化而来的心理机制，在现代国家、组织与决策者中传播并根深蒂固。即便如今过度自信不再能带来益处，这也有助于解释过度自信与战争之间频繁出现的关联。