The adaptive value of trivial giving: it signals one’s trustworthiness

– by Yuta Kawamura & Misato Inaba

In Japan, there exists a customary practice known as “oseibo”. This is a year-end gift given to a relative, colleague, boss, subordinate, or business partner with whom one shares a somewhat close relationship. In many cases, both parties exchange gifts of similar value that are not excessively costly. Typically, these gifts consist of food items that anyone can purchase (e.g., cooking oil). The exchange of oseibo between two parties rarely occurs just once; instead, it continues for several years or even longer.

Beyond the specific example of oseibo, such social exchanges are common in human society. People sometimes bestow gifts on each other or engage in food sharing with their partners. Nevertheless, these behaviors seem peculiar from the perspectives of direct reciprocity. According to the theory of direct reciprocity, for reciprocal relationship to be maintained, the benefits of cooperation (b) must outweigh the costs paid by the actor (c) (b/c > 1). In other words, social exchange must generate additional benefits. However, the mutual giving described above does not yield any further benefit (b/c = 1): regardless of whether gifts are exchanged or consumed separately, total gain for the two remains constant. This raises the question: why do people continue to exchange such seemingly meaningless gifts?

Our research team investigated the adaptive value of such trivial giving—small-stakes giving that does not yield any further benefit. Our hypothesis was that trivial giving functions as a signal of trustworthiness: that is, trivial giving serves as an indication that the actor is a cooperative person. Consider, for example, facing a natural disaster. To overcome the difficulties, prompt cooperation with neighbors becomes imperative. However, would you trust a neighbor whom you do not know at all? If you regularly show trustworthiness to each other by giving small gifts, you can enhance cooperation more expeditiously.

There is another perspective, however: people may not simply distinguish between trivial and nontrivial giving (i.e., cooperation). Despite receiving trivial gifts, some people might feel gratitude and try to reciprocate. Certain social emotion, such as empathy and gratitude, which may have evolved to facilitate cooperation, may malfunction even in the context of trivial giving.

To examine these competing hypotheses, it will be necessary to assess whether the frequency of trivial giving changes depending on the need to show trustworthiness. If trivial giving functions as a signal of trustworthiness, the behavior should be more likely to occur when there is a need to show that the actor is a cooperative person. We designed a newly modified Prisoner’s Dilemma (PD) experiment. The experiment linked two types of trials: trivial giving trials and cooperation trials. The cooperative trials followed the traditional PD structure. Participants were to decide whether to give 1,000 points to the partner, and if they did, the endowment was multiplied by three (i.e., b/c = 3). In trivial giving trials, however, participants were to decide whether to give relatively small stake (100 points) to the partner or keep it for themselves, and the total payoff remained the same regardless of their choice (i.e., b/c = 1). Participants repeated these trials with their assigned partners. The interaction was over with a one-twentieth probability.

In the real world, a combination of trivial giving and cooperation is commonly observed. Opportunities for trivial giving arise on a daily basis, while unforeseen challenges requiring cooperation to overcome them, such as natural disasters, occur less frequently. To simulate this scenario, the experiment was comprised of a high frequency of trivial giving trials (seven-eighths) and a low frequency of cooperation trials (one-eighths).

Additionally, we manipulated the need to show trustworthiness. In the experimental condition, participants were assigned the same partner for both trivial giving and cooperation trials. In the control condition, participants were assigned a different partner for each type of trial. Thus, while the payoff matrices were identical in both conditions, only in the experimental condition could participants show their trustworthiness in trivial giving trials toward the partner in a future cooperation trial.

The laboratory experiment involving eighty-four Japanese participants revealed that participants are more inclined to engage in trivial giving when they anticipate future opportunities for cooperation with their partners. This result suggests that trivial giving, seemingly meaningless acts, functions as a signal of trustworthiness. However, the experiment was constrained to specific contexts, leaving uncertainty over its applicability in the intricate real world. Considering the context of daily life, people can decide for themselves the magnitude of the signaling costs. Also, in some societies, people have the agency to easily exchange their partners. Further studies should integrate these real-world elements into experiments. Despite these limitations, our findings illuminate the significance of trivial giving, revealing it as a subtle yet powerful signal of trustworthiness that may underpin the fabric of human cooperation.

Read the original article: Kawamura, Y., & Inaba, M. (2023). Trivial giving as a signal of trustworthiness. Evolution & Human Behavior, 44(4), 332-338.