– 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.

– by James R. Roney

In many nonhuman mammals, females emit clear cues of time periods when they are able to conceive: from large sexual swellings in some primates, to odors that reveal ovulatory timing. In humans, overt signaling of this kind appears absent, and scientists like Don Symons and Beverly Strassmann theorized that concealment of ovulatory timing may have facilitated the evolution of human pair bonding. Nonetheless, a series of studies have provided evidence that women smell more attractive near ovulation (reviewed here), raising the possibility that although the cues are more subtle than in nonhuman species, perhaps human ovulatory timing is not completely concealed. So, which is it, concealed or not?

In prior research, my lab used signal detection theory to test whether attractiveness shifts in women’s odors were substantial enough for perceivers to accurately diagnose ovulatory timing. The intuition is this: even if odors collected near ovulation smell better than odors collected at other times on average, is there still enough overlap in fertile vs. non-fertile odor attractiveness that perceivers cannot reliably categorize whether an odor sample was produced during the fertile window (the fertile window is defined as cycle days when conception is possible)? Our findings provided evidence for just such a conclusion: even for samples from the same woman, the signal detection analyses showed so much overlap in fertile vs. non-fertile sample ratings that attractiveness ratings could not diagnose fertile window odors with any appreciable accuracy.

A limitation of the above study was that its findings apply only to conscious perceptions of odor attractiveness. But adaptations designed to respond to odor cues of ovulatory timing do not have to produce subjective impressions of odor attractiveness. As long as those mechanisms respond to such cues in functional ways (for instance, by priming sexual desire or courtship efforts), then human ovulatory timing may be effectively unconcealed. And indeed, some prior research had provided evidence that men may respond to women’s ovulatory scents with increases in hormones and sexual thoughts. Perhaps, then, something really subtle is going on: men accurately diagnose ovulatory timing through subconscious hormonal and psychological responses.

We sought to test a replication of such hormonal and psychological responses in a recent study. Women collected both underarm and genital scent samples on 6 nights spaced five days apart over a period of 30 days. We chose 28 women odor donors with confirmed ovulation in their collection cycles and drew samples from three cycle regions from each woman: during the fertile window, before the fertile window (the follicular phase), and after the fertile window (the luteal phase). One hundred eighty-two male raters were randomly assigned to each smell one of the odor samples (or plain water as a control) and each odor sample was smelled by one man. We collected saliva samples before and after the smelling in order to test for reactive changes in men’s testosterone and cortisol, and we also collected a series of post-stimulus survey measures that assessed the priming of sexual concepts, attribution of sexual arousal to the women scent donors, sexual desire, and motivation to approach others.

The statistical tests most directly relevant to the question of concealed ovulation are those that compare responses to the fertile window stimuli to the responses to all other stimuli. None of those tests produced statistically significant results in this study. Thus, we found no evidence that men respond differently to ovulatory scent cues in terms of hormonal or psychological responses. Bayesian follow-up analyses also suggested strong evidence in favor of the null hypothesis for all dependent variables. These findings occurred despite our study generally having greater statistical power than prior studies that reported positive findings.

Our results differed from some reported in prior studies, and so further research on the question of adaptive responses to ovulatory scent cues could provide important additional evidence. Nonetheless, when considered together with our prior work using signal detection analyses to assess cycle phase shifts in scent attractiveness, the findings from this study suggest that body odors do not reveal women’s ovulatory timing.

Of course, scents are just one sensory modality through which ovulatory timing might be perceived. Cycle phase shifts in faces, voices, and behaviors also have some empirical support, although prior studies have not always rigorously determined ovulatory timing in such studies via use of biological markers (such as urinary luteinizing hormone tests, which were used in the research profiled in this blog post). Future research that both precisely determines ovulatory timing and applies signal detection analyses to any observed cycle phase shifts may lead to a more rigorous set of conclusions regarding the concealment of human ovulatory timing.

Read the original article: Roney, J. R., Mei, M., Grillot, R. L., & Emery Thompson, M. (2023). No effects of exposure to women’s fertile window body scents on men’s hormonal and psychological responses. Evolution and Human Behavior, 44(4), 305-314.

– by Carlton Patrick

When Clarence Thomas was nominated to serve on the United States Supreme Court, it was Joe Biden, then a Senator from Delaware, who chaired the Senate Judiciary Committee and oversaw the confirmation process. During the hearing, Biden questioned Thomas at length on his views on natural law, saying that while the discussion might “confound the people…whether someone applies natural law is of phenomenal significance, and there is not a single legal scholar you can question who would not tell you that is not true.”

To understand why Senator Biden was so invested in this line of questioning, it is helpful to consider the category of legal disputes that the philosopher Ronald Dworkin calls hard cases. These are instances where a judge must decide a novel controversy that isn’t determined by an existing statute or case law and so the judge must therefore make new law herself. There are countless variations of what principle the judge could use to decide the case. She could decide the case in a way that produces the most equitable or egalitarian result. She could make law that would maximize economic efficiency. Or she could make law that would emphasize conflict reduction, or safety maximization, for example.

But adherents to the natural law philosophy—a list that not only includes Justice Thomas, but also Aristotle, St. Thomas Aquinas, Hugo Grotius, and John Locke—posit that a true, objective set of moral principles exists out in the universe and that laws are only valid to the extent that they conform to this set of principles. Thus, in the face of a hard case, the judge cannot choose among orthogonal principles, and instead must make the positive (or man-made) law accord with the objective natural law that wafts through the ether. Otherwise, the law is simply not valid.

Where do we look to determine these objective principles of natural law? For a long time the dominant theory was that these principles emanate from God(s). Modern defenders of the natural law approach point to a variety sources including Gods, the universe, moral truths, and other metaphysical sources. Regardless of the source, though, most natural law proponents agree that there are certain universal values that are revealed to us through instinct and intuition, and that, as the legal philosopher Jonthan Crowe phrases it “we are characteristically disposed to pursue…and regard them as normatively worthwhile.” Justice Thomas phrases it this way: “the thesis of natural law is that human nature provides the key to how men ought to live their lives.”

What I argue in my article Evolution is the Source, and the Undoing, of Natural Law, is that there is danger in this sort of thinking. Rather than automatically deferring to our gut intuitions, we should investigate where they come from, and use that as the jumping off point for policy discussions about how to make law.

The natural law philosophy derives much of its momentum from the fact that our moral intuitions seem immutable. They are often widely shared, instinctual, robust to temporal and cultural differences. They emerge early in childhood, and are impervious to counter-argument. And it is true that legal codes from vastly different cultures and from different millennia have common features, lending credence to  Cicero’s assertion that the law is “not one thing at Rome, and another thing at Athens” but is instead “universal…unchanging and everlasting.”

But these phenomena can be explained without resorting to superstition. Thirty years of empirically validated evolutionary studies have provided us with a scientific framework for explaining that the reason we share so many moral intuitions, that they show up early in development, and that take on a deontological force is that they are part of our species-wide psychological architecture. They helped to navigate the conflicts inherent in the highly social world of our ancestors where censuring certain actions while praising others would have had significant social consequences. For example, our moral conscience—the intuition that personally taking an action would be the “right” or “wrong” thing to do—helps us accrue praise and reputational clout while avoiding condemnation and punishment. Likewise, our intuitions of justice facilitate the proactive condemnation (and reactive punishment) of certain behaviors by marking those behaviors as ‘wrong’ and attaching an intuitive degree of severity to their wrongness.

Cast in this light, the rubber-stamping of intuition into law urged by the natural law philosophy begins to take on a different view, and many will immediately recognize this as a version of the naturalistic fallacy. By automatically incorporating our moral intuitions into law, we are saying that simply because something evolved, it is per se good, and per se worth institutionalizing. But these intuitions—like all of our intuitions—exist not because they were passed down from a divine arbiter of truth, but instead because they likely granted some fitness advantage to their holder. And, as a result, these intuitions—like all of our intuitions—have the potential to lead us in a wayward direction.

Just as our folk intuitions of physics, economics, or probability can lead us to irrational, inaccurate, or counter-productive conclusions, our moral intuitions can be similarly flawed. They can be selfish, nepotistic, myopic, and capricious. We think the same action is more wrong when it’s done by someone outside of our political group, and less wrong when it’s one of our comrades. We are mortified at the thought of our neighbor’s child dying of hunger but are unmoved when it routinely happens to children living in a Cambodian slum. We flip-flop our moral positions when there is money or reputational benefit associated with doing so. In other words, when consistency in moral judgments runs up against the self-interest of the person making the moral judgment, it is self-interest that often prevails.

In evolutionary terms, these quirks of our moral intuitions are features, not bugs. They would have likely been quite advantageous in terms of navigating the types of recurrent conflicts of interests our ancestors faced. There are no doubt evolutionary advantages to favoring our political allies and our neighbors, or to endorsing different moral positions when doing so would result in a greater economic or coalitional position for us. But, I argue, the fact that our moral intuitions are skewed in these directions is reason enough to give us pause, and to require an argument why (as opposed to a presumption that) they should be used in lawmaking.

Read the original article: Patrick, C. (2023). Evolution is the source, and the undoing, of natural law. Evolution & Human Behavior, 44(3), 175-183.

This article is part of a special issue of Evolution & Human Behavior on Evolution, Justice and Law, edited by Debra Lieberman & Keelah Williams.

– by Peter DeScioli

Why do humans make so many laws? In a new article, I argue that the human ability to make laws evolved by natural selection. I hope to entice you with a few snapshots.

Laws may seem unlikely to come from evolution. There are so many laws, and they differ so much across societies. This variation shows that natural selection did not install a single code of laws in the human mind. We do not have ten commandments, or five or twenty, etched into our minds, or else we would see the same code of laws repeated in society after society.”

But does this mean that human evolution has little to tell us about the origin of laws? Not at all. To see why, just compare laws to tools. Humans make countless tools, and tools vary tremendously across societies. Yet, it is well-understood that humans evolved adaptations to make and use tools. The human mind does not have a fixed set of blueprints for ten or twenty tools. Rather, natural selection installed in the mind principles of physics and engineering that humans use to make new tools for new purposes. The same is true of laws: Humans evolved a creative power to make limitless laws by applying a stock of core principles. Humans are lawmakers like we are toolmakers.

With this in mind, we can dissect a sample of laws to find the common parts that humans use to make them. The parts of laws are ideas that we compose into messages, such as Thou shalt not kill, and Whosoever lieth with a beast shall surely be put to death (Exodus, 22:19). Some of the ideas that come up repeatedly include indefinite people such as thou and whosoever, actions such as kill, steal, and lie with, intentions such as wanting and planning, as well as truth, impartiality, possibility, necessity, punishment, and proportion.

Having laid out the parts of laws, we can then inspect them for clues about their evolutionary purpose. What is all this lawmaking for? How do humans use laws in evolutionary competition?

We first consider an apparent likeness between laws and threats. Threats are well-understood signals in games of conflict, and like laws, threats warn of punishment that is conditional on some event, such as If you come any closer, then I will punch you. However, on close inspection, we find that threats and laws differ in each of their parts. For instance, threats address a definite person while laws address an indefinite person, and threats are enforced by the threatener while laws are enforced by the whole community. Given these and other differences, we conclude that laws are not the same as threats, and thus cannot be explained by theories of threats.

Next, we compare laws to moral rules and find a close match:

Like laws, moral rules apply to everyone, they set a condition that is a specific action and requires evidence, they concern an infinite variety of actions, they are enforced by everyone with blame and punishment, and the punishment is proportionate. Moral rules match laws part for part. (DeScioli, 2023, p. 199)

Given this correspondence, we conclude that laws are produced by moral judgment. Moreover, I have previously argued that moral judgment evolved as a strategy for choosing sides in conflicts. Humans use the moral strategy to avoid some of the dangers of choosing sides by alliances and hierarchies. In the moral strategy, people choose sides by rules of action, like opposing a thief according to the rule, Thou shalt not steal, rather than choosing sides by alliances or hierarchy, such as supporting an ally or superior who stole someone’s goods. And since moral judgment is the source of laws, the parts of laws are also patterned by the same function: choosing sides in conflicts while avoiding the dangers of alliances and hierarchy.

Hence, we have found the origin of laws in our strategies for choosing sides. But we are not finished. The ability to make laws creates new games and spurs a multitude of strategies and counterstrategies:

The evolution of laws is not the end of the game but only the beginning. Once humans can compose laws to settle conflicts, the next problem is that they can make too many…. As prolific lawmakers, humans can easily produce a multiplicity of laws too numerous to remember and too discordant to apply. (p. 202)

To prevent a chaotic proliferation of laws, humans evolved the ability to debate which laws to accept into the community’s code and which to reject. Moreover, each person judges potential laws according to their own interests, so people inevitably disagree on many laws, giving rise to a battle to control the laws.

When many people disagree on a law, it is unstable and varies over time and across societies.… Locked in disagreement, the opponents struggle in a tug of war to control the law. (p. 202)

Last, I illustrate the competition to control the laws by examining common skirmishes over laws of violence, property, sex, factions, and power. In each case, we see how opponents struggle to enact opposite laws, meaning laws that would punish opposite sides in a conflict. We also encounter what I call paradoxical laws, such as Thou shalt not betray our faction. Paradoxical laws mimic the characteristic form of laws despite the fact that they undermine the rule of law in general, replacing it with the rule of faction or hierarchy.

The struggle to control the laws also damages science, because committed partisans condemn facts and ideas that could weaken the case for the laws they favor. Indeed, this may be why “the science of human evolution itself has long been accused of subverting the foundations of morality and society” (p. 207). In closing, I offer a defense against this charge:

In defense, it may help to point out that human evolution does not affirm a single code of laws but rather explains why humans make a great variety of laws and then fight to control them. (p. 207)

Read the original article here: DeScioli, P. (2023). On the origins of laws by natural selection. Evolution and Human Behavior, 44(3), 195-209.

This article is part of a special issue of Evolution & Human Behavior on Evolution, Justice and Law, edited by Debra Lieberman & Keelah Williams