Evolution favours positively biased reasoning in sequential interactions with high future gains.

Empirical evidence shows that human behaviour often deviates from game-theoretical rationality. For instance, humans may hold unrealistic expectations about future outcomes. As the evolutionary roots of such biases remain unclear, we investigate here how reasoning abilities and cognitive biases coevolve using the evolutionary game theory. In our model, individuals in a population deploy a variety of unbiased and biased level-[Formula: see text] reasoning strategies to anticipate others' behaviour in sequential interactions, represented by the incremental centipede game. Positively biased reasoning strategies have a systematic inference bias towards higher but uncertain rewards, while negatively biased strategies reflect the opposite tendency. We find that selection consistently favours positively biased reasoning, with rational behaviour even going extinct. This bias coevolves with bounded rationality, as the reasoning depth remains limited in the population. Interestingly, positively biased agents may coexist with non-reasoning agents, thus pointing to a novel equilibrium. Longer games further promote positively biased reasoning, as they can lead to higher future rewards. The biased reasoning strategies proposed in this model may reflect cognitive phenomena like wishful thinking and defensive pessimism. This work therefore supports the claim that certain cognitive biases, despite deviating from rational judgement, constitute an adaptive feature to better cope with social dilemmas.