In this blog post, we’ll examine how human altruistic behavior manifests through the reciprocity hypothesis and what limitations it has.

The Relationship Between the Reciprocity Hypothesis and Altruistic Behavior

There are spaces that everyone uses together, such as school restrooms or playgrounds near our homes. We cannot claim these spaces as our own or prevent or restrict others from using them. Spaces or objects used by multiple people in this way are called public goods.
Let’s assume there is no one to clean these spaces. In that case, the people using the public goods would have to take responsibility for cleaning them themselves. However, this raises the question of who will be responsible for cleaning. This is because, regardless of whether a public space is kept clean or not, those who do not participate in cleaning can gain a relatively greater benefit. If the number of people who pursue only their own interests and refuse to clean increases, the public good will eventually become increasingly dirty, and ultimately, no one will be able to use that space. As such, if everyone acts selfishly, the community cannot be sustained.
However, in real-world society, not everyone acts purely selfishly. In fact, many people engage in altruistic behavior, such as shoveling snow in front of their own house and then sweeping the area in front of their neighbor’s house as well. So why do people choose altruistic behavior over selfish behavior, which could yield greater benefits?
There are various hypotheses explaining why altruistic behavior occurs, one of which is the “reciprocity hypothesis.” The core of the reciprocity hypothesis is the “tit-for-tat” strategy, in which one responds exactly as the other person behaves. If the other person defies, I defy in return; if the other person cooperates, I cooperate as well.
This strategy is known to have performed exceptionally well in computer simulation studies designed to find the most efficient strategy in the Prisoner’s Dilemma game, where players choose between cooperation and defiance to earn points based on the outcome. Even though betrayal may seem like the more advantageous option in some situations, the fact that this strategy has yielded good results demonstrates that acting purely selfishly is not always the most advantageous choice in society.
From this, we can infer that people act altruistically because they expect the other person to act altruistically in return. In other words, the reason I give someone a cookie is because I expect to receive a piece of chocolate from them in return. The behavior of chimpanzees grooming each other—a common sight at zoos—is also sometimes explained not simply as a way to help one another, but as a means to secure food or exchange favors in the future. The same applies to humans. The act of lending notes to a friend who couldn’t come to school or accompanying a friend to the infirmary may also be influenced to some extent by this principle of reciprocity. This means that such actions are taken in the expectation of receiving help in a similar situation later on.

Limitations of the Reciprocity Hypothesis and Group Projects

Problems can arise because altruistic behavior is predicated on a reciprocal altruistic response from the other party. A prime example is group projects. In a group project, multiple people work together on a single assignment and are jointly evaluated on the results. Therefore, the group’s overall performance often serves as the evaluation criterion rather than individual effort. In such situations, selfish behavior—such as free-riding—may occur.
Since group projects are usually completed only once before the group composition changes, even if a group member fails to cooperate, there is no opportunity to reciprocate in the same way with that person in the future. Consequently, the “tit-for-tat” strategy described in the reciprocity hypothesis is unlikely to function effectively.
Altruistic behavior is effective only when there is an expectation that the other party will also act altruistically. However, since the groups are reshuffled afterward, if someone attempts to free-ride, other group members may be less inclined to actively participate in the task, which can ultimately result in the task not being completed properly. This example illustrates a limitation of the reciprocity hypothesis: namely, that the “tit-for-tat” strategy may not be effective when the same situation does not recur.
The “repeated reciprocity hypothesis” was proposed to address this limitation. This hypothesis posits that the “tit-for-tat” strategy is effective only when it is applied over a sufficiently long period of time and involves interactions with partners with whom one maintains a long-term relationship. If these conditions are met, the strategy outlined by the reciprocity hypothesis can be highly effective.

What aspects does the reciprocity hypothesis fail to explain?

So far, we have examined the “reciprocity hypothesis,” one of the theories explaining the reasons behind altruistic behavior in humans. The core of the reciprocity hypothesis is the “tit-for-tat” strategy, which involves mirroring the other party’s behavior in one’s next action. However, this approach has the limitation that it is less effective in situations where interactions occur only a few times. To address this, the “repeated reciprocity hypothesis” was developed by adding the conditions that interactions occur repeatedly and that a long-term relationship is maintained with the other party.
The repeated reciprocity hypothesis is highly effective at explaining altruistic behavior in situations involving repeated interactions. However, it cannot fully account for altruistic behavior that occurs in non-repeated situations. To address this limitation, various theories—such as the “group selection hypothesis” and the “kin selection hypothesis”—have been proposed.