– by Diego Guevara Beltrán, Jessica Ayers, Lee Cronk, & Athena Aktipis

Thirty-four experts on cooperation walk into a bar and begin to discuss the ‘true’ meaning of the term ‘reciprocity.’ A biologist offers one definition. She says, “we observe reciprocity when the gift of some food, or another favor, increases the probability for the donor to receive the same thing, or something else, from the receiver”.

Perhaps because that approximates one of Robert Trivers’ definitions of reciprocal altruism, all experts nod in agreement with the biologist. However, not being quite content with this definition, an economist retorts “[that the] formulation is rather sloppy.” His colleague adds that “reciprocity should be conceptualized as reciprocal strategies in repeated games, normative obligations, and individual preferences to respond to kind acts with kind acts and to unkind acts with unkind acts.”

“Yes, yes, but how do we operationalize reciprocity?” asks one psychologist. He says, “The best statistical definition is the contemporaneous correlation of two individuals’ responses within time-series regression analyses and as partner effects among these variables.” Intrigued but bewildered, another psychologist adds “reciprocity is reciprocity, that’s what I was taught! Because he gave to him and he gave to me, then I gave to her, albeit indirectly. But I couldn’t keep track of who gave what to whom, what I owed to him, or who I should groom. Maybe we should just avoid this definitional animosity and just call all transfers something-something reciprocity!”

A review of the literature yields a proliferation of reciprocity-related terms – thirty-four at last count. That might lead you to believe that experts indeed agreed with the bewildered psychologist. Perhaps experts want to avoid definitional animosity and decided to call all transfers “something-something” reciprocity. With several conflicting, overlapping, and even a few redundant terms, it was clear there is no consensus among scholars regarding what truly constitutes reciprocity. In fact, these terms continue to proliferate, as evidenced by the preceding paper in the same issue of Evolution and Human Behavior (i.e., “dynamic indirect reciprocity”). This lack of consensus and the continued proliferation of terms motivated us to review the term reciprocity and survey cooperation experts about it.

In our study, we asked 85 cooperation experts to rate the extent to which they believe thirty scholarly definitions of the term reciprocity were truly reciprocity. Some of these definitions (e.g., indirect reciprocity: return is expected from someone other than recipient of benefit) are common in the literature, while others (e.g., homeomorphic reciprocity: exchange of things that are the same) not so much.

We first wanted to know whether experts’ responses would help us identify underlying dimensions of reciprocity (i.e., characteristics that cluster some, but not other, terms together). Applying factor analyses, we find that the scholarly definitions of the term reciprocity can be represented by four broad dimensions: (1) Balanced Transfers (i.e., transfers that are of equal or equivalent value), (2) Reputation-based Transfers (i.e., transfers where individuals give to others who have given in the past and receive from others if they have given in the past, (3) Debt-based Transfers (i.e., transfers where individuals keep track of, and expect repayment for, what they give to others), and (4) Unconditional Transfers (i.e., transfers that do not revolve around concepts of debt or account keeping). This four-factor framework captures greater variation in types, or dimensions, of transfers than previous frameworks (e.g., direct, indirect, and generalized reciprocity).

We encourage experts to consider adopting these terms. In doing so, we can provide specific qualifiers to a transfer while at the same time reducing the possible number of dimensions that describe a transfer based on whether, or the extent to which, they are balanced, debt-based, reputation-based, or unconditional. For example, we saw that several experts used the same term (e.g., indirect reciprocity) to describe multiple different reciprocity terms. Hence, our framework would allow experts to avoid using overlapping terms to describe different dimensions of transfers, ultimately improving communication within and between disciplines.

We then assessed the level of consensus among experts regarding what truly constitutes reciprocity. There was no consensus regarding what should be considered reciprocity. However, over 90% of experts agreed that unconditional transfers (e.g., generalized reciprocity I: non-conditional sharing and giving of assistance) should not be considered reciprocity. So, although experts do not yet agree on what truly constitutes reciprocity, these findings suggest that the scholarly community can move beyond discussions of whether unconditional transfers should or should not be considered reciprocity. They should not be.

Instead, the scholarly community might consider focusing on outstanding disagreements, such as those identified in our study. For example, some experts believe that transfers are reciprocity only if agents have the intention to reward a giver or incentivize a receiver to give back, while others do not think intentionality is a defining feature of reciprocity. Similarly, some experts believe that reciprocity must involve a cost, while others believe that reciprocity does not involve cost or transfers with negative utility.

Focusing on these issues might help experts reach a consensus regarding what truly constitutes reciprocity. However, we might also supersede these disagreements by adopting the language of Balanced, Debt-based, Reputation-based, and Unconditional transfers. Does it matter for the study of evolution and human behavior whether unconditional giving is or is not reciprocity? We think not. What matters is that we reach a deeper understanding of the ultimate causes and proximate mechanisms underlying the diversity of transfers that have shaped the evolution of human behavior. While our framework does not include information about the ultimate causes of behavior, it provides information about the proximate mechanisms underlying an individual’s decision to engage in a transfer. Overall, we hope our study allows the scientific community to gauge the current level of consensus, or lack thereof, regarding the term reciprocity, and ease communication across academic fields.

Read the original article: Guevara Beltrán, D., Ayers, J.D., Munoz, A., Cronk, L., & Aktipis, A. (2023). What is reciprocity? A review and expert-based classification of cooperative transfers. Evolution & Human Behavior, 44(4), 384-393.

– by Léo Fitouchi (Image credit Frans Huby, Creative Commons 3.0)

Humans want wrongdoers to suffer. From the justice courts of modern societies to the biblical “eye for an eye,” people everywhere have rules for punishing transgressions including theft, murder, assault, or property damage. Why do human societies punish wrongdoers? You might think the answer is simple: to teach offenders a lesson so that they don’t offend again and the group can function well.

This intuition—that punishment serves to enforce collective norms—reflects in many strands of social science. Émile Durkheim, the French founder of sociology, argued that punishment serves to reaffirm the sacred values of the group, thereby reinforcing group solidarity. More recently, evolutionary social scientists assume that humans feel the need to punish norm-violators even when their behavior doesn’t harm the punisher directly—a behavior called third-party punishment. We humans would be normative animals, deeply committed to getting deviants back in line, for the good of the group and at a cost to oneself.

In this view, third-party punishment is not only a universal feature of human psychology; it also explains why humans are so cooperative compared to other species. By imposing costs on antisocial actors, third-party punishment would have selected for higher levels of cooperation during human evolution.

Despite these wide-ranging claims, however, few recent studies have examined how punishment operates in the social contexts where our punitive psychology is assumed to have evolved—namely, small-scale, politically decentralized societies (for notable exceptions, see here, here, and here). Most studies of punishment rely on participants from large-scale societies or, if they include participants from small-scale societies, on artificial experiments such as economic games.

In a recent paper, Manvir Singh and I examine the concrete enactment of punishment in three small-scale societies: Kiowa bison hunters (North America), Mentawai horticulturalists (Indonesia), and Nuer pastoralists (South Sudan). We code ethnographic reports of 91 offenses among the Kiowa, analyze first-hand interviews about 276 offenses among the Mentawai, and review punitive procedures documented among the Nuer.

With find that punitive procedures are often inconsistent with a norm-enforcement function. Most notably, people don’t bother punishing violations that don’t harm them directly. The quasi-totality of the punishments we observe, whether they involve fines, killing the offender, or destroying their property, are administered by the victim themselves or their family in retaliation for the harm suffered. Contrary to the idea that third-party punishment is universal and has shaped the evolution of human cooperation, people often seem indifferent to transgressions that do not affect them directly, even for serious transgressions such as murder.

If people do not punish to enforce collective norms or group cooperation, then what is punishment for? A useful analogy here is the distinction, made in some large-scale societies, between criminal law and civil law. Criminal law deals with violations of the society’s norms, which are punished by third-party officials on behalf of society as a whole. Civil law, by contrast, deals with dyadic disputes between private parties, requiring the offender to compensate the victim for the tort inflicted. Punitive justice in small-scale societies, we argue, serves only the civil function of resolving private disputes between offender and victim and restoring their cooperative relationship that was broken by the offense.

Offenses such as theft, murder, or adultery typically trigger retaliation on the part of the victim—a behavior evolved to deter future exploitation. Yet unrestrained retaliation can trigger counter-punishment on the part on of offender, which risks escalating into destructive feuds that end up harming not only disputants themselves, but also their kin or allies, who often get embroiled in the conflict. People have thus had a mutual interest in designing and retaining punitive procedures that seemed well-suited to reconciling disputants and limiting conflict between offender and victim after offenses.

Our results show that the justice systems of the Kiowa, the Mentawai, and the Nuer exhibit many features consistent with this restorative function. First, punishment was entangled with compensation: the offender had to pay costs, yes, but often while providing the victim with material benefits such as pigs, cattle, horses, or other valuables. This allows the victim to experience forgiveness and appeases their urge for revenge, preventing harsh retaliations that could spark destructive feuds. Second, the prescribed level of punishment and compensation was proportionate to the tort inflicted on the victim. This, again, is well suited to satisfy the victim’s urge for revenge while avoiding disproportionate retaliation that could spark counter-revenge. Third, while third parties rarely punished, they often intervened to mediate, pacify disputants, and help them achieve peaceful resolution.

Our results echo longstanding observations of legal anthropologists. For decades, researchers working in small-scale, politically decentralized societies have insisted on the rarity of third-party punishment, the private nature of law, and the compensatory logic of justice. Yet these features of punishment have been largely ignored by evolutionary social scientists and psychologists, leading to misleading assumptions about the evolution of punishment and cooperation. Rather than third-party punishers enforcing cooperation, as often occurs in large-scale, anonymous societies, social order in most human societies may have been far more decentralized, emerging from individuals and families negotiating over how to best treat each other.

Read the original paper: Fitouchi, L., & Singh, M. (2023). Punitive justice serves to restore reciprocal cooperation in three small-scale societies. Evolution & Human Behavior, 44(5), 502-514.

– by Victor Vikram Odouard

Driving my Fiat 500 convertible through the Swiss countryside surrounding Geneva, a sign caught my eye. In large hand written letters, it read “CAiSSE” – “CHeCKOUT” in French. Behind the sign, a heap of pumpkins lay on a threadbare canvas blanket. But unlike most checkouts, no one was there. And unlike most self-checkouts, there were no cameras in sight. No, this little Hofladen relied on the honor system.

Why wasn’t there a horde of pumpkin bandits raiding our humble farmstand?

Scientists have proposed many mechanisms to explain the evolution of altruistic behavior, such as kin altruism, punishment, and direct & indirect reciprocity. These all share a common characteristic: they provide a second-order benefit to altruists, that compensates for the initial cost.

Most of these mechanisms require knowledge of who is cooperating (I will sometimes call altruistic behavior cooperation in this post). Sometimes that knowledge can come from observation, as is the case with reciprocity (I know who did me a favor in the past). But other mechanisms, like third party punishment and indirect reciprocity, require that knowledge of who has cooperated spread to those who were unlikely to observe the interactions in question. This requires a faithful communication system (read: gossip!) that accurately transmits the relevant information.

And here we arrive at the question we pose in this paper: why should we even have such a communication system, when it might be in people’s interests to lie?

The question echoes the original cooperation question – “why should people benefit society by acting altruistically when it can come at a personal cost?” Here, we simply replace “acting altruistically” with “communicating truthfully”. The parallel points to a solution – perhaps the same mechanism that keeps people cooperative can also keep people communicative.

In our paper, we analyze a model of indirect reciprocity to determine whether such a mechanism can exist. Imagine an agent, Ariel. She meets someone else, Blake, and she can make a choice: she can cooperate or defect. If Ariel cooperates, she pays a cost in order to produce a benefit for Blake. Let’s say she does cooperate. Afterwards, Blake can “gossip” about Ariel’s behavior, in this case, “Ariel good”, since she cooperated. In the next interaction, when Ariel meets Corina, and Corina is deciding whether to cooperate with Ariel, Corina is aware of Blake’s gossip – in this case, that Ariel cooperated. Blake’s gossiping thus produces Ariel’s reputation. Corina can then, for example, decide to cooperate with Ariel since she cooperated with Blake. This is indirect reciprocity.

The twist in our model is that the indirect reciprocity “twists back” on itself: instead of reputations being based solely on how agents act, they can also be based on how agents gossip. How does this work? Returning to our previous scenario, let’s say Ariel cooperates with Blake, but Blake nonetheless says that “Ariel bad”. Perhaps someone, Diana, saw the whole thing go down, and she communicates “Blake bad”, because he lied. In Blake’s next interaction, with Ed, Ed could therefore decide not to cooperate with Blake.

In this scenario, the machinery being used to maintain cooperation (accurate communication) is being co-opted to maintain itself! In our paper, we ask whether such a self-referential system can actually lead to a stable, high-cooperation state, and we found that yes, it could, in the case where (1) agents made occasional (but not too frequent) errors and (2) the norm punishes defection while nonetheless being self-consistent. Both of these conditions will require further explanation.

The first condition reflects an important fact about many complex systems, which is that heterogeneity can enhance stability: for instance, a virus often has a harder time sweeping through a population with many diverse immune responses to its infection, as it must circumvent many different types of defenses. Taking this one step further, if a population has been infected by many different sorts of viruses in the past, it can mount a diversity of different immune responses to any new pathogen – thus, a diversity of past “disturbances” (viruses, in this case), can make a population more robust by diversifying its immune defenses. This is exactly what we see in our model, where error introduces diversity by causing, for instance, some defections, or some untruthful gossip, where they wouldn’t usually occur. We found that this diversity of small-scale disturbances inoculates the system against more serious destabilizing forces.

As for the second condition, a norm in our setting is a determination of whether a given action is good or bad. A gossip system can encode such a norm: for instance, it might call cooperation and truthfulness “good” and defection and untruthfulness “bad”. Agents can then respond to those judgments: for instance, in one of the above examples, Blake was deemed “bad” for having lied about Ariel, and Diana therefore refused to cooperate with him. But a question arises: does the norm judge Diana’s action, which is in effect enforcing the norm (cooperating with those who followed the truthfulness norm, defecting with those who didn’t), as good? In this simple case, no – defection is considered bad. So Diana is judged as “bad” under the very norm that she is enforcing! This norm is therefore not self-consistent – a norm is self-consistent if it does reward the actions enforcing it. A self-consistent norm instead might deem cooperating with “good” agents good, and defecting with “bad” agents good, and everything else “bad”. This norm, called stern judging, is self-consistent, because it rewards the behaviors that enforce it. For instance, there are some societies that consider theft to be permissible if committed against people in bad standing in the community (for instance, people who unjustifiably stole from someone else). This is a self-consistent norm, as the punishment of individuals in bad standing is permissible under the norm’s own rules.

In our analysis, we find that maintenance of cooperation and communication requires such a self-consistent norm. This highlights that for decentralized norm enforcement, self-consistency is critical. If norm enforcement is centralized, self-consistency need not apply, as different rules may exist for judging the centralized body of enforcers and everyone else. For instance, most people judge killing to be bad, but in some countries, this judgment does not apply to a government doling out the death penalty. However, with decentralized norm enforcement, the people who enforce the norms are the people, and therefore no such distinction can exist. Self-consistency is thus needed.

Our study is fundamentally about whether a self-contained norm-enforcement system, not buttressed by anything external, can maintain high levels of cooperation. The external buttress that provoked our study was communication – most indirect reciprocity models assume an already-truthful communication system. But by noticing here that communicating truthfully is not so different from cooperating (in that both provide a public good), we hypothesized that the same indirect reciprocity mechanism enforcing cooperation could enforce truthful communication, without relying on a preexisting communication. The two conditions under which such a state was stable emphasize other important properties of a self-contained norm enforcement system. First, that it can “create its own diversity”, through error, allowing the system to function without being propped up by some external source of diversity. And second, that the norm is able to “reward its own enforcers”, by being self-consistent – this allows enforcement to occur without requiring a separate body of enforcers, operating under different rules.

Read the original article: Odouard, V.V., & Price, M.H. (2023). Tit for tattling: cooperation, communication, and how each could stabilize the other. Evolution & Human Behavior, 44(4), 359-372.

– 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.