In this blog post, we’ll examine what the Repeated Reciprocity Hypothesis is—using examples of altruistic behavior in everyday life and blood-sharing among vampire bats—and explore how this hypothesis explains altruistic behavior and what its limitations are.
You probably have memories of going on a trip with friends at least once during your school days. One of the concerns that arises when traveling in a group is the issue of costs—specifically, who will pay how much for a trip taken together. The most efficient method is to set up a common fund and pay for expenses from there. However, tragedy strikes when people are so caught up in the excitement of the trip that they fail to think of this solution, or when an awkward number of people—such as three—gather to pool their money. Since not all travel expenses are divided exactly by N, it’s inevitable that during the trip, some people will end up paying less while others pay more. For example, if three people go on a trip and the taxi fare comes to $6, each person should pay $2. In reality, however, one person might pay the entire taxi fare upfront, and the other two could settle the account later by each covering their share of $2. However, there may be cases where the person who is supposed to receive the money—or the one who is supposed to give it—forgets to settle the account. Or, if someone dislikes having to say, “Can you give me the $2 you owe me from earlier?” every time they’re in the middle of enjoying the trip, they might not get properly reimbursed for the taxi fare they paid upfront. If that happens, the person who paid the taxi fare will inevitably be the only one to lose out. As a result, this person set out with a similar amount of money as their two traveling companions, but by the time they return home, they will be the only one left with relatively less money. I certainly noticed that one of my friends was contributing less during the trip, but I didn’t bring it up. Why did I choose not to address this issue, even though I was at a financial disadvantage? One way to interpret this phenomenon is through the Repeated Reciprocity Hypothesis.
The repeated reciprocity hypothesis is one method for analyzing the causes of altruistic behavior among people. Let’s examine a phenomenon observed among vampire bats. Vampire bats are animals that survive by feeding on the blood of other animals. Therefore, every night, they go out hunting to obtain the blood they need to survive. However, these hunting trips are not always successful. There will always be bats that fail to catch prey. So, do bats that have failed to hunt for several days simply starve to death? No. Bats that have successfully hunted regurgitate the blood they have consumed and share it with the hungry bats, thereby preventing their starving companions from dying. This behavior is known as a classic example of altruism, in which an individual shares food obtained through its own efforts with another without expecting anything in return. One might wonder if, according to the kin selection hypothesis, these bats show kindness to one another because they are related. However, it has been found that blood-sharing among vampire bats occurs even between unrelated individuals. Given this, some clever bats might reason that since their fellow bats supply them with blood, there is no need for them to go out hunting themselves. However, it is difficult to explain blood-sharing among vampire bats simply as free-riding. Biologist G. S. Wilkinson closely observed vampire bats, tracking the behavior of the bat that shared blood (A) and the bat that received it (B), and discovered that when A later became hungry, it was highly likely to receive help from B. In other words, when a bat finds itself in a difficult situation, it receives help from another bat—and that bat is often one it had helped in the past. The bat shares its blood with a hungry fellow bat now in anticipation of a time when it might be hungry in the future. The repeated reciprocity hypothesis interprets this behavior as altruistic action in the present, driven by the expectation of future rewards.
The reason why the person mentioned earlier in the introduction did nothing even after suffering a financial loss can also be explained by the repeated reciprocity hypothesis. Let’s consider the act of paying more money by the person mentioned in the introduction as an altruistic act. According to the repeated reciprocity hypothesis, the reason that person acted altruistically during the trip is that he had previously received help from another friend—the one who paid less—or because he anticipated benefits from that friend after the trip ended. If he had publicly stated, “My friend OO is paying less, and that bothers me,” there is a possibility that his relationship with that friend would have deteriorated. From a long-term perspective, since maintaining a good relationship with his friend is beneficial in terms of interpersonal dynamics, he likely refrained from publicly revealing the truth in order to secure the future reward of a good friendship. In other words, he judged that maintaining the friendship—even while incurring an immediate financial loss—would yield greater long-term benefits for himself. Of course, friendships cannot be described in such a cold and simplistic manner, but based on the repeated reciprocity hypothesis, this behavior can also be explained as altruistic action arising from the expectation of future mutual benefits.
To summarize briefly, the repeated reciprocity hypothesis posits that present altruistic behavior arises from the expectation of future rewards. If you’re familiar with the saying “an eye for an eye, a tooth for a tooth,” you’ll find this concept easy to understand because it’s similar. Furthermore, it has the advantage of explaining cooperation and altruistic behavior between non-kin individuals—phenomena that are difficult to account for using the kin selection hypothesis alone. However, the repeated reciprocity hypothesis also has its limitations. It fails to adequately explain why people engage in altruistic behavior even when there is little or no chance of receiving a future reward. For example, in the United States, it is customary to leave a tip after eating at a restaurant. If we interpret this custom through the repeated reciprocity hypothesis, we might conclude that people leave tips because they expect good service from the waiter who served them the next time they visit that restaurant. But what about a customer from a distant foreign country who leaves a tip? The likelihood that they will revisit that restaurant is very low. Even if they were to return months or years later, it is unlikely that the waiter who served them would still be working there, or that the waiter would remember that the customer had tipped them in the past and provide good service as a result. Nevertheless, the fact that travelers do sometimes leave tips demonstrates that there are behaviors that cannot be explained by simple reciprocity alone. These limitations can be addressed by other hypotheses regarding altruistic behavior, such as the group selection theory and the “birds of a feather flock together” theory.
