Super-additive cooperation.

Repeated interactions provide an evolutionary explanation for one-shot human cooperation that is counterintuitive but orthodox1-3. Intergroup competition4-7 provides an explanation that is intuitive but heterodox. Here, using models and a behavioural experiment, we show that neither mechanism reliably supports cooperation. Ambiguous reciprocity, a class of strategies that is generally ignored in models of reciprocal altruism, undermines cooperation under repeated interactions. This finding challenges repeated interactions as an evolutionary explanation for cooperation in general, which further challenges the claim that repeated interactions in the past can explain one-shot cooperation in the present. Intergroup competitions also do not reliably support cooperation because groups quickly become extremely similar, which limits scope for group selection. Moreover, even if groups vary, group competitions may generate little group selection for multiple reasons. Cooperative groups, for example, may tend to compete against each other8. Whereas repeated interactions and group competitions do not support cooperation by themselves, combining them triggers powerful synergies because group competitions constrain the corrosive effect of ambiguous reciprocity. Evolved strategies often consist of cooperative reciprocity with ingroup partners and uncooperative reciprocity with outgroup partners. Results from a behavioural experiment in Papua New Guinea fit exactly this pattern. They thus suggest neither an evolutionary history of repeated interactions without group competition nor a history of group competition without repeated interactions. Instead, our results suggest social motives that evolved under the joint influence of both mechanisms.

Changing cultural attitudes towards female genital cutting.

As globalization brings people with incompatible attitudes into contact, cultural conflicts inevitably arise. Little is known about how to mitigate conflict and about how the conflicts that occur can shape the cultural evolution of the groups involved. Female genital cutting is a prominent example. Governments and international agencies have promoted the abandonment of cutting for decades, but the practice remains widespread with associated health risks for millions of girls and women. In their efforts to end cutting, international agents have often adopted the view that cutting is locally pervasive and entrenched. This implies the need to introduce values and expectations from outside the local culture. Members of the target society may view such interventions as unwelcome intrusions, and campaigns promoting abandonment have sometimes led to backlash as they struggle to reconcile cultural tolerance with the conviction that cutting violates universal human rights. Cutting, however, is not necessarily locally pervasive and entrenched. We designed experiments on cultural change that exploited the existence of conflicting attitudes within cutting societies. We produced four entertaining movies that served as experimental treatments in two experiments in Sudan, and we developed an implicit association test to unobtrusively measure attitudes about cutting. The movies depart from the view that cutting is locally pervasive by dramatizing members of an extended family as they confront each other with divergent views about whether the family should continue cutting. The movies significantly improved attitudes towards girls who remain uncut, with one in particular having a relatively persistent effect. These results show that using entertainment to dramatize locally discordant views can provide a basis for applied cultural evolution without accentuating intercultural divisions.

Promotion of behavioural change for health in a heterogeneous population.

Public health policy often involves implementing cost-efficient, large-scale interventions. When mandating or forbidding a specific behaviour is not permissible, public health professionals may draw on behaviour change interventions to achieve socially beneficial policy objectives. Interventions can have two main effects: (i) a direct effect on people initially targeted by the intervention; and (ii) an indirect effect mediated by social influence and by the observation of other people's behaviour. However, people's attitudes and beliefs can differ markedly throughout the population, with the result that these two effects can interact to produce unexpected, unhelpful and counterintuitive consequences. Public health professionals need to understand this interaction better. This paper illustrates the key principles of this interaction by examining two important areas of public health policy: tobacco smoking and vaccination. The example of antismoking campaigns shows when and how public health professionals can amplify the effects of a behaviour change intervention by taking advantage of the indirect pathway. The example of vaccination campaigns illustrates how underlying incentive structures, particularly anticoordination incentives, can interfere with the indirect effect of an intervention and stall efforts to scale up its implementation. Recommendations are presented on how public health professionals can maximize the total effect of behaviour change interventions in heterogeneous populations based on these concepts and examples.

Les politiques de santé publique impliquent souvent l'organisation de campagnes rentables à grande échelle. Lorsqu'il est impossible d'imposer ou d'interdire certains comportements, les professionnels de la santé publique ont parfois recours à des actions induisant un changement de comportement afin d'atteindre des objectifs bénéfiques pour la société. Ces actions sont susceptibles d'entraîner deux effets: (i) un effet direct sur les personnes initialement visées par la campagne; et (ii) un effet indirect provoqué par la pression sociale et l'observation du comportement d'autres personnes. Néanmoins, les attitudes et croyances peuvent considérablement varier au sein de la population; ainsi, ces deux effets peuvent interagir et avoir des conséquences imprévues, inefficaces et contre-intuitives. Les professionnels de la santé publique ont besoin de mieux comprendre cette interaction. Le présent document en illustre donc les principes majeurs en examinant deux domaines clés des politiques de santé publique: le tabagisme et la vaccination. L'exemple des campagnes antitabac montre quand et comment les acteurs de la santé publique peuvent accentuer l'impact d'une action destinée à faire évoluer les comportements en optant pour l'approche indirecte. L'exemple des campagnes de vaccination met en lumière la manière dont les structures d'incitation sous-jacentes, en particulier celles favorisant l'anticoordination, peuvent interférer avec l'effet indirect d'une action et anéantir les efforts déployés pour la mettre en œuvre. Plusieurs recommandations sont formulées afin d'aider les professionnels de la santé publique à amplifier l'effet global des actions de changement comportemental au sein d'une population hétérogène, en s'appuyant sur ces concepts et exemples.

La política de salud pública suele incluir la aplicación de intervenciones rentables y a gran escala. Cuando no es posible imponer o prohibir un comportamiento específico, los profesionales de la salud pública pueden recurrir a intervenciones de cambio de comportamiento para lograr objetivos políticos que sean favorables para la sociedad. Es posible que las intervenciones generen dos efectos principales: i) un efecto directo sobre las personas a las que en principio se dirige la intervención; y ii) un efecto indirecto mediado por la influencia social y por la observación del comportamiento de otras personas. Sin embargo, las actitudes y creencias de las personas pueden ser muy diferentes en toda la población, por lo que estos dos efectos pueden interactuar y producir consecuencias inesperadas, poco útiles y contraproducentes. Los profesionales de la salud pública deben comprender mejor esta interacción. Este documento explica los principios clave de esta interacción al analizar dos áreas importantes de la política de salud pública: el tabaquismo y la vacunación. El ejemplo de las campañas antitabaco muestra cuándo y cómo los profesionales de la salud pública pueden aumentar los efectos de una intervención de cambio de comportamiento si se aprovecha el procedimiento indirecto. El ejemplo de las campañas de vacunación explica cómo las estructuras subyacentes de incentivos, en particular los incentivos de descoordinación, pueden interferir con el efecto indirecto de una intervención y detener los esfuerzos para ampliar su aplicación. A partir de estos conceptos y ejemplos, se formulan recomendaciones sobre cómo los profesionales de la salud pública pueden maximizar el efecto total de las intervenciones de cambio de comportamiento en poblaciones heterogéneas.

Investigating the Structure of Son Bias in Armenia With Novel Measures of Individual Preferences.

Sex ratios at birth favoring boys are being documented in a growing number of countries, a pattern indicating that families selectively abort females. Son bias also explains why, in many countries, girls have more siblings and are born at relatively earlier parities compared with their brothers. In this study, we develop novel methods for measuring son bias using both questionnaire items and implicit association tests, and we collect data on fertility preferences and outcomes from 2,700 participants in Armenia. We document highly skewed sex ratios, suggesting that selective abortions of females are widespread among parents in our sample. We also provide evidence that sex-selective abortions are underreported, which highlights the problem of social desirability bias. We validate our methods and demonstrate that conducting implicit association tests can be a successful strategy for measuring the relative preference for sons and daughters when social desirability is a concern. We investigate the structure of son-biased fertility preferences within households, across families, and between regions in Armenia, using measures of son bias at the level of the individual decision-maker. We find that men are, on average, considerably more son-biased than women. We also show that regional differences in son bias exist and that they appear unrelated to the socioeconomic composition of the population. Finally, we estimate the degree of spousal correlation in son bias and discuss whether husbands are reliably more son-biased than their wives.

Behavioural homogenization with spillovers in a normative domain.

The importance of culture for human social evolution hinges largely on the extent to which culture supports outcomes that would not otherwise occur. An especially controversial claim is that social learning leads groups to coalesce around group-typical behaviours and associated social norms that spill over to shape choices in asocial settings. To test this, we conducted an experiment with 878 groups of participants in 116 communities in Sudan. Participants watched a short film and evaluated the appropriate way to behave in the situation dramatized in the film. Each session consisted of an asocial condition in which participants provided private evaluations and a social condition in which they provided public evaluations. Public evaluations allowed for social learning. Across sessions, we randomized the order of the two conditions. Public choices dramatically increased the homogeneity of normative evaluations. When the social condition was first, this homogenizing effect spilled over to subsequent asocial conditions. The asocial condition when first was thus alone in producing distinctly heterogeneous groups. Altogether, information about the choices of others led participants to converge rapidly on similar normative evaluations that continued to hold sway in subsequent asocial settings. These spillovers were at least partly owing to the combined effects of conformity and self-consistency. Conformity dominated self-consistency when the two mechanisms were in conflict, but self-consistency otherwise produced choices that persisted through time. Additionally, the tendency to conform was heterogeneous. Females conformed more than males, and conformity increased with the number of other people a decision-maker observed before making her own choice.

Sustained cooperation by running away from bad behavior.

For cooperation to evolve, some mechanism must limit the rate at which cooperators are exposed to defectors. Only then can the advantages of mutual cooperation outweigh the costs of being exploited. Although researchers widely agree on this, they disagree intensely about which evolutionary mechanisms can explain the extraordinary cooperation exhibited by humans. Much of the controversy follows from disagreements about the informational regularity that allows cooperators to avoid defectors. Reliable information can allow cooperative individuals to avoid exploitation, but which mechanisms can sustain such a situation is a matter of considerable dispute. We conducted a behavioral experiment to see if cooperators could avoid defectors when provided with limited amounts of explicit information. We gave each participant the simple option to move away from her current neighborhood at any time. Participants were not identifiable as individuals, and they could not track each other's tendency to behave more or less cooperatively. More broadly, a participant had no information about the behavior she was likely to encounter if she moved, and so information about the risk of exploitation was extremely limited. Nonetheless, our results show that simply providing the option to move allowed cooperation to persist for a long period of time. Our results further show that movement, even though it involved considerable uncertainty, allowed would-be cooperators to assort positively and eliminate on average any individual payoff disadvantage associated with cooperation. This suggests that choosing to move, even under limited information, can completely reorganize the mix of selective forces relevant for the evolution of cooperation.

Identifying culture as cause: Challenges and opportunities.

Causal inference lies at the core of many scientific endeavours. Yet answering causal questions is challenging, especially when studying culture as a causal force. Against this backdrop, this paper reviews research designs and statistical tools that can be used - together with strong theory and knowledge about the context of study - to identify the causal impact of culture on outcomes of interest. We especially discuss how overlooked strategies in cultural evolutionary studies can allow one to approximate an ideal experiment wherein culture is randomly assigned to individuals or entire groups (instrumental variables, regression discontinuity design, and epidemiological approach). In doing so, we also review the potential outcome framework as a tool to engage in causal reasoning in the cultural evolutionary field.

How culture shapes choices related to fertility and mortality: Causal evidence at the Swiss language border.

Results from cultural evolutionary theory often suggest that social learning can lead cultural groups to differ markedly in the same environment. Put differently, cultural evolutionary processes can in principle stabilise behavioural differences between groups, which in turn could lead selection pressures to vary across cultural groups. Separating the effects of culture from other confounds, however, is often a daunting and sometimes intractable challenge for the working empiricist. To meet this challenge, we exploit a cultural border dividing Switzerland in ways that are independent of institutional, environmental and genetic variation. Using a regression discontinuity design, we estimate discontinuities at the border in terms of preferences related to fertility and mortality, the two basic components of genetic fitness. We specifically select six referenda related to health and fertility and analyse differences in the proportion of yes votes across municipalities on the two sides of the border. Our results show multiple discontinuities and thus indicate a potential role of culture in shaping stable differences between groups in preferences and choices related to individual health and fertility. These findings further suggest that at least one of the two groups, in order to uphold its cultural values, has supported policies that could impose fitness costs on individuals relative to the alternative policy under consideration.

Isolating a culture of son preference among Armenian, Georgian and Azeri Parents in Soviet-era Russia.

A basic hypothesis is that cultural evolutionary processes sustain differences between groups, these differences have evolutionary relevance and they would not otherwise occur in a system without cultural transmission. The empirical challenge is that groups vary for many reasons, and isolating the causal effects of culture often requires appropriate data and a quasi-experimental approach to analysis. We address this challenge with historical data from the final Soviet census of 1989, and our analysis is an example of the epidemiological approach to identifying cultural variation. We find that the fertility decisions of Armenian, Georgian and Azeri parents living in Soviet-era Russia were significantly more son-biased than those of other ethnic groups in Russia. This bias for sons took the form of differential stopping rules; families with sons stopped having children sooner than families without sons. This finding suggests that the increase in sex ratios at birth in the Caucasus, which began in the 1990s, reflects a cultural preference for sons that predates the end of the Soviet Union. This result also supports one of the key hypotheses of gene-culture coevolution, namely that cultural evolutionary processes can support group-level differences in selection pressures that would not otherwise occur in a system without culture.

When norm change hurts.

Applied cultural evolution includes any effort to mobilize social learning and cultural evolution to promote behaviour change. Social tipping is one version of this idea based on conformity and coordination. Conformity and coordination can reinforce a harmful social norm, but they can also accelerate change from a harmful norm to a beneficial alternative. Perhaps unfortunately, the link between the size of an intervention and social tipping is complex in heterogeneous populations. A small intervention targeted at one segment of society can induce tipping better than a large intervention targeted at a different segment. We develop and examine two models showing that the link between social tipping and social welfare is also complex in heterogeneous populations. An intervention strategy that creates persistent miscoordination, exactly the opposite of tipping, can lead to higher social welfare than another strategy that leads to tipping. We show that the potential benefits of miscoordination often hinge specifically on the preferences of people most resistant to behaviour change. Altogether, ordinary forms of heterogeneity complicate applied cultural evolution considerably. Heterogeneity weakens both the link between the size of a social planner's intervention and behaviour change and the link between behaviour change and the well-being of society. This article is part of the theme issue 'Social norm change: drivers and consequences'.

What is the extent of a frequency-dependent social learning strategy space?

Models of frequency-dependent social learning posit that individuals respond to the commonality of behaviours without additional variables modifying this. Such strategies bring important trade-offs, e.g. conformity is beneficial when observing people facing the same task but harmful when observing those facing a different task. Instead of rigidly responding to frequencies, however, social learners might modulate their response given additional information. To see, we ran an incentivised experiment where participants played either a game against nature or a coordination game. There were three types of information: (a) choice frequencies in a group of demonstrators; (b) an indication of whether these demonstrators learned in a similar or different environment; and (c) an indication about the reliability of this similarity information. Similarity information was either reliably correct, uninformative or reliably incorrect, where reliably correct and reliably incorrect treatments provided participants with equivalent earning opportunities. Participants adjusted their decision-making to all three types of information. Adjustments, however, were asymmetric, with participants doing especially well when conforming to demonstrators who were reliably similar to them. The overall response, however, was more fluid and complex than this one case. This flexibility should attenuate the trade-offs commonly assumed to shape the evolution of frequency-dependent social learning strategies.

Group identities can undermine social tipping after intervention.

Social tipping can accelerate behaviour change consistent with policy objectives in diverse domains from social justice to climate change. Hypothetically, however, group identities might undermine tipping in ways that policymakers do not anticipate. To examine this, we implemented an experiment around the 2020 US federal elections. The participants faced consistent incentives to coordinate their choices. Once the participants had established a coordination norm, an intervention created pressure to tip to a new norm. Our control treatment used neutral labels for choices. Our identity treatment used partisan political images. This simple pay-off-irrelevant relabelling generated extreme differences. The control groups developed norms slowly before intervention but transitioned to new norms rapidly after intervention. The identity groups developed norms rapidly before intervention but persisted in a state of costly disagreement after intervention. Tipping was powerful but unreliable. It supported striking cultural changes when choice and identity were unlinked, but even a trivial link destroyed tipping entirely.

Wrath of God: religious primes and punishment.

Recent evidence indicates that priming participants with religious concepts promotes prosocial sharing behaviour. In the present study, we investigated whether religious priming also promotes the costly punishment of unfair behaviour. A total of 304 participants played a punishment game. Before the punishment stage began, participants were subliminally primed with religion primes, secular punishment primes or control primes. We found that religious primes strongly increased the costly punishment of unfair behaviours for a subset of our participants--those who had previously donated to a religious organization. We discuss two proximate mechanisms potentially underpinning this effect. The first is a 'supernatural watcher' mechanism, whereby religious participants punish unfair behaviours when primed because they sense that not doing so will enrage or disappoint an observing supernatural agent. The second is a 'behavioural priming' mechanism, whereby religious primes activate cultural norms pertaining to fairness and its enforcement and occasion behaviour consistent with those norms. We conclude that our results are consistent with dual inheritance proposals about religion and cooperation, whereby religions harness the byproducts of genetically inherited cognitive mechanisms in ways that enhance the survival prospects of their adherents.

Collectively jumping to conclusions: Social information amplifies the tendency to gather insufficient data.

False beliefs can spread within societies even when they are costly and when individuals share access to the same objective reality. Research on the cultural evolution of misbeliefs has demonstrated that a social context can explain what people think but not whether it also explains how people think. We shift the focus from the diffusion of false beliefs to the diffusion of suboptimal belief-formation strategies and identify a novel mechanism whereby misbeliefs arise and spread. We show that, when individual decision makers have access to the data-gathering behavior of others, the tendency to make decisions on the basis of insufficient evidence is amplified, increasing the rate of incorrect, costly decisions. We argue that this mechanism fills a gap in current explanations of problematic, widespread misbeliefs such as climate change denial. (PsycInfo Database Record (c) 2022 APA, all rights reserved).

Other-regarding preferences in a non-human primate: common marmosets provision food altruistically.

Human cooperation is unparalleled in the animal world and rests on an altruistic concern for the welfare of genetically unrelated strangers. The evolutionary roots of human altruism, however, remain poorly understood. Recent evidence suggests a discontinuity between humans and other primates because individual chimpanzees do not spontaneously provide food to other group members, indicating a lack of concern for their welfare. Here, we demonstrate that common marmoset monkeys (Callithrix jacchus) do spontaneously provide food to nonreciprocating and genetically unrelated individuals, indicating that other-regarding preferences are not unique to humans and that their evolution did not require advanced cognitive abilities such as theory of mind. Because humans and marmosets are cooperative breeders and the only two primate taxa in which such unsolicited prosociality has been found, we conclude that these prosocial predispositions may emanate from cooperative breeding.

The evolution of distorted beliefs vs. mistaken choices under asymmetric error costs.

Why do people sometimes hold unjustified beliefs and make harmful choices? Three hypotheses include (a) contemporary incentives in which some errors cost more than others, (b) cognitive biases evolved to manage ancestral incentives with variation in error costs and (c) social learning based on choice frequencies. With both modelling and a behavioural experiment, we examined all three mechanisms. The model and experiment support the conclusion that contemporary cost asymmetries affect choices by increasing the rate of cheap errors to reduce the rate of expensive errors. Our model shows that a cognitive bias can distort the evolution of beliefs and in turn behaviour. Unless the bias is strong, however, beliefs often evolve in the correct direction. This suggests limitations on how cognitive biases shape choices, which further indicates that detecting the behavioural consequences of biased cognition may sometimes be challenging. Our experiment used a prime intended to activate a bias called 'hyperactive agency detection', and the prime had no detectable effect on choices. Finally, both the model and experiment show that frequency-dependent social learning can generate choice dynamics in which some populations converge on widespread errors, but this outcome hinges on the other two mechanisms being neutral with respect to choice.

The promise and the peril of using social influence to reverse harmful traditions.

For a policy-maker promoting the end of a harmful tradition, conformist social influence is a compelling mechanism. If an intervention convinces enough people to abandon the tradition, this can spill over and induce others to follow. A key objective is thus to activate such spillovers and amplify an intervention's effects. With female genital cutting as a motivating example, we develop empirically informed analytical and simulation models to examine this idea. Even if conformity pervades decision-making, spillovers can range from irrelevant to indispensable. Our analysis highlights three considerations. First, ordinary forms of individual heterogeneity can severely limit spillovers, and understanding the heterogeneity in a population is essential. Second, although interventions often target samples of the population biased towards ending the harmful tradition, targeting a representative sample is a more robust way to achieve spillovers. Finally, if the harmful tradition contributes to group identity, the success of spillovers can depend critically on disrupting the link between identity and tradition.