In this blog post, we’ll explore the “Birds of a Feather” hypothesis, which explains altruistic behavior based on sacrifice depicted in movies and game theory.
Have you seen the movie ‘Saving Private Ryan’? In this film, Captain Miller and his eight-man squad are sent on an extremely dangerous mission to rescue a single soldier, Private Ryan. Some of the soldiers even lose their lives in the process of rescuing him. How can we explain this altruistic behavior—sacrificing one’s own life to save another? One of the leading theories that explains this is the “Birds of a Feather Hypothesis.”
Before explaining the “Birds of a Feather” hypothesis, it is necessary to first understand a game theory concept known as the “Prisoner’s Dilemma.” The “Prisoner’s Dilemma” is a theory that explains the choices two prisoners—facing punishment for alleged complicity—will make when their sentences depend on whether they confess or not. The key point of this theory is that the two prisoners cannot communicate with each other. If both prisoners deny the crime, they each receive a 5-year sentence; if only one confesses, the confessor goes unpunished, while the one who denies the crime receives a 20-year sentence. Conversely, if both confess, they each receive a 10-year sentence. In this situation, since confessing is more advantageous regardless of the other person’s choice, both prisoners ultimately choose to confess. This is often cited as a classic example illustrating human self-interest. However, in real society, not everyone acts purely out of self-interest. This is because there are indeed instances, such as the soldiers in ‘Saving Private Ryan’, where people risk their own lives to save others.
The “birds of a feather flock together” hypothesis posits that altruistic and selfish people each tend to gather and interact with others who share similar tendencies. Applying this to game theory, a person who chooses a cooperative strategy reaps the greatest benefit when interacting with others who have also chosen a cooperative strategy. Conversely, a person who chooses a defection strategy is more likely to receive the lowest payoff when repeatedly interacting with others who have chosen the same defection strategy. In other words, the more people with similar tendencies interact with one another, the more cooperative behavior is maintained and can gradually develop in a stable manner. Furthermore, the “birds of a feather flock together” hypothesis is linked to various research findings on human interaction. Research has also shown that when choosing a spouse or colleague, people tend to place greater importance on cultural characteristics or behavioral patterns than on physical traits. In other words, if altruism and selfishness are viewed as behavioral traits, it stands to reason that people with similar tendencies are more likely to associate with one another.
The “birds of a feather flock together” hypothesis becomes even more persuasive if two people can determine, to some extent, whether the other person is altruistic or selfish before they interact. This is because altruistic individuals are naturally more likely to seek out other altruistic people, even when seeking to maximize their own interests. In real life, people often verify whether a counterpart is trustworthy before making a transaction or assess whether someone is reliable by observing their behavior. Examples of this can be seen in online transactions, where buyers check a seller’s credibility, or in situations where people meet in person before a transaction to verify the other party.
Another explanation is that since individuals who choose a defection strategy harm the interests of the group as a whole, social norms may serve to exclude or isolate selfish individuals from the group. These various phenomena can also be understood as evidence supporting the “birds of a feather flock together” hypothesis.
By now, your curiosity about why altruistic behavior occurs should have been somewhat satisfied. The “birds of a feather flock together” hypothesis explains the tendency of people who prefer cooperative behavior to associate with others who share similar tendencies when situations like the “Prisoner’s Dilemma” recur. By focusing on the fact that players can choose their opponents in game theory, this hypothesis provides a compelling explanation for why altruistic behavior can be maintained and developed.
