Exploitation by asymmetry of information reference in coevolutionary learning in prisoner's dilemma game.

Mutual relationships, such as cooperation and exploitation, are the basis of human and other biological societies. The foundations of these relationships are rooted in the decision making of individuals, and whether they choose to be selfish or altruistic. How individuals choose their behaviors can be analyzed using a strategy optimization process in the framework of game theory. Previous studies have shown that reference to individuals' previous actions plays an important role in their choice of strategies and establishment of social relationships. A fundamental question remains as to whether an individual with more information can exploit another who has less information when learning the choice of strategies. Here we demonstrate that a player using a memory-one strategy, who can refer to their own previous action and that of their opponent, can be exploited by a reactive player, who only has the information of the other player, based on mutual adaptive learning. This is counterintuitive because the former has more choice in strategies and can potentially obtain a higher payoff. We demonstrated this by formulating the learning process of strategy choices to optimize the payoffs in terms of coupled replicator dynamics and applying it to the prisoner's dilemma game. Further, we show that the player using a memory-one strategy, by referring to their previous experience, can sometimes act more generous toward the opponent's defection, thereby accepting the opponent's exploitation. Mainly, we found that through adaptive learning, a player with limited information usually exploits the player with more information, leading to asymmetric exploitation.