In this blog post, I’ll summarize how the repeated reciprocity hypothesis explains the evolutionary origins of altruism, as well as its limitations and complementary factors in the real world.
Questions Raised by Literary Imagination
The plot of a novel depicting a city where an epidemic spreads, causing people to lose their sight, stimulates the intuition that humans act altruistically by adhering to morals and norms through the “self” as seen in the eyes of others. The idea that altruism would disappear if others could no longer recognize us seems to many to serve as evidence of human innate selfishness.
However, some scientists argue that altruism may also be a trait that has been selected for during the course of evolution. In other words, the logic goes that if people who exhibited altruistic behavior survived and reproduced more successfully in society than those who did not, that trait could have been passed down to future generations. Since elucidating the origins of altruism provides crucial clues for understanding humans and society, various hypotheses have been proposed, and among them, the most widely discussed is the Repeated Reciprocity Hypothesis.
What Is the Repeated Reciprocity Hypothesis?
The repeated reciprocity hypothesis is based on the principle of reciprocity—that is, conditional cooperation, where “if you cooperate with me, I will cooperate with you next time.” It argues that if one employs a strategy of rewarding cooperation and retaliating against betrayal, cooperation becomes advantageous in the long run, thereby sustaining altruistic behavior.
To illustrate this principle, consider the relationship between a supermarket owner and customers. If a supermarket owner overcharges customers, they will stop shopping at that store, and ultimately, the owner will suffer losses in the long run. A customer’s decision to stop shopping at the supermarket can be seen as retaliation for the owner’s betrayal, and the greater the likelihood of retaliation, the more cooperatively people tend to behave.
Why Repeatability and Uncertainty Are Important
The key point is that for repeat-reciprocity to hold, transactions must be repeated. If there are not enough repetitions, the short-term gains from free-riding outweigh the long-term losses, making it rational to choose to defect. However, even more important than the “number” of repetitions is the uncertainty that participants face—they do not know when the transactions will end.
For example, if the number of transactions is fixed at exactly 10, it is rational for both parties to defect in the final transaction; this fact then affects the preceding transactions, leading to the paradoxical conclusion that defection occurs in every transaction. Conversely, if the end point of the transactions is uncertain and there is a high probability they will continue, the cost of defection increases, making cooperation more advantageous.
Limitations of the Repeated Reciprocity Hypothesis
While the Repeated Reciprocity Hypothesis has the advantage of explaining cooperation in non-kin relationships—which is difficult to account for through blood ties—it does not apply to all situations. In particular, its explanatory power weakens in situations where interactions are not repeated or in interactions involving multiple parties.
For example, a customer leaving a tip at a restaurant in a tourist destination—knowing they will not return—is an act of altruism arising from a one-time transaction, but it is difficult to explain using the Repeated Reciprocity Hypothesis. Furthermore, in interactions involving many people, it is difficult to retaliate individually against a single person’s betrayal, making it hard to resolve the free-rider problem. If retaliation also harms altruistic actors, or if free-riders face only relatively mild sanctions, cooperation is likely to break down.
Three Factors That Strengthen Retaliation in Real Life
Real-world societies differ from simple theoretical models and possess several factors that enhance the effectiveness of retaliation. First is indirect reciprocity. This refers to the practice of excluding or cooperating with a specific person or group based on information obtained from others, even if one has not been directly affected. For example, if a rumor spreads that a supermarket owner is overcharging customers, many people will avoid that store.
Second, in reality, it is often possible to identify who the free-riders are, allowing for more selective and efficient sanctions.
If it is possible to identify who has violated the norm, the community can restore cooperation through targeted retaliation.
Third, people tend to penalize those who deviate from the norm, regardless of whether the transaction is repeated. In other words, there is a psychological tendency to punish betrayers or antisocial behavior, even at one’s own expense. This tendency contributes to maintaining norms and justice, and ensures that cooperation is maintained to some extent even in situations where repetition is not guaranteed.
Conclusion: How Is Altruism Explained?
In summary, the repeated reciprocity hypothesis provides a rational explanation for why altruistic behavior becomes evolutionarily stable when transactions are sustained and relationships with others are long-term. The uncertainty of transactions and the prospect of long-term losses act as deterrents against betrayal, serving as a crucial mechanism that compels us to adhere to social norms and cooperate.
However, this hypothesis alone does not fully explain one-time interactions or the free-rider problem within large groups. Nevertheless, since real-world factors such as indirect reciprocity, identifiability, and the tendency toward normative punishment play a complementary role, there is a strong possibility that we can maintain an altruistic and cooperative society as long as we can identify our counterparts.
