Charles Efferson

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 Coevolution of Cultural Groups and Ingroup Favoritism

Cultural boundaries have often been the basis for discrimination, nationalism, religious wars, and genocide. Little is known, however, about how cultural groups form or the evolutionary forces behind group affiliation and ingroup favoritism. Hence, we examine these forces experimentally and show that arbitrary symbolic markers, though initially meaningless, evolve to play a key role in cultural group formation and ingroup favoritism because they enable a population of heterogeneous individuals to solve important coordination problems. This process requires that individuals differ in some critical but unobservable way and that their markers be freely and flexibly chosen. If these conditions are met, markers become accurate predictors of behavior. The resulting social environment includes strong incentives to bias interactions toward others with the same marker, and subjects accordingly show strong ingroup favoritism. When markers do not acquire meaning as accurate predictors of behavior, players show a markedly reduced taste for ingroup favoritism. Our results support the prominent evolutionary hypothesis that cultural processes can reshape the selective pressures facing individuals and so favor the evolution of behavioral traits not previously advantaged.

Redefine Statistical Significance

We propose to change the default P-value threshold for statistical significance from 0.05 to 0.005 for claims of new discoveries.

Beyond existence and aiming outside the laboratory: estimating frequency-dependent and pay-off-biased social learning strategies

The existence of social learning has been confirmed in diverse taxa, from apes to guppies. In order to advance our understanding of the consequences of social transmission and evolution of behaviour, however, we require statistical tools that can distinguish among diverse social learning strategies. In this paper, we advance two main ideas. First, social learning is diverse, in the sense that individuals can take advantage of different kinds of information and combine them in different ways. Examining learning strategies for different information conditions illuminates the more detailed design of social learning. We construct and analyse an evolutionary model of diverse social learning heuristics, in order to generate predictions and illustrate the impact of design differences on an organisms fitness. Second, in order to eventually escape the laboratory and apply social learning models to natural behaviour, we require statistical methods that do not depend upon tight experimental control. Therefore, we examine strategic social learning in an experimental setting in which the social information itself is endogenous to the experimental group, as it is in natural settings. We develop statistical models for distinguishing among different strategic uses of social information. The experimental data strongly suggest that most participants employ a hierarchical strategy that uses both average observed pay-offs of options as well as frequency information, the same model predicted by our evolutionary analysis to dominate a wide range of conditions.

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.

Impartial Institutions, Pathogen Stress and the Expanding Social Network

Anthropologists have documented substantial cross-society variation in people’s willingness to treat strangers with impartial, universal norms versus favoring members of their local community. Researchers have proposed several adaptive accounts for these differences. One variant of the pathogen stress hypothesis predicts that people will be more likely to favor local in-group members when they are under greater infectious disease threat. The material security hypothesis instead proposes that institutions that permit people to meet their basic needs through impartial interactions with strangers reinforce a tendency toward impartiality, whereas people lacking such institutions must rely on local community members to meet their basic needs. Some studies have examined these hypotheses using self-reported preferences, but not with behavioral measures. We conducted behavioral experiments in eight diverse societies that measure individuals’ willingness to favor in-group members by ignoring an impartial rule. Consistent with the material security hypothesis, members of societies enjoying better-quality government services and food security show a stronger preference for following an impartial rule over investing in their local in-group. Our data show no support for the pathogen stress hypothesis as applied to favoring in-groups and instead suggest that favoring in-group members more closely reflects a general adaptive fit with social institutions that have arisen in each society.

Viewing men's faces does not lead to accurate predictions of trustworthiness

The evolution of cooperation requires some mechanism that reduces the risk of exploitation for cooperative individuals. Recent studies have shown that men with wide faces are anti-social, and they are perceived that way by others. This suggests that people could use facial width to identify anti-social men and thus limit the risk of exploitation. To see if people can make accurate inferences like this, we conducted a two-part experiment. First, males played a sequential social dilemma, and we took photographs of their faces. Second, raters then viewed these photographs and guessed how second movers behaved. Raters achieved significant accuracy by guessing that second movers exhibited reciprocal behaviour. Raters were not able to use the photographs to further improve accuracy. Indeed, some raters used the photographs to their detriment; they could have potentially achieved greater accuracy and earned more money by ignoring the photographs and assuming all second movers reciprocate.

Are Religious Individuals More Generous, Trusting, and Cooperative? An Experimental Test of the Effect of Religion on Prosociality

We investigated the effect of religion on generosity, interpersonal trust, and cooperation by using games developed by experimental economists (Dictator, Trust, and Public Goods). In these experiments, individuals were paired or grouped with unknown strangers to test the degree to which religion promotes prosocial behavior. We evaluated group- and individual-level effects of religion on prosocial behavior across the three games. Although playing the games in a religious setting showed no overall difference as compared to a secular setting, we did find a weak association between some individual-level dimensions of religiosity and behavior in some of the games. The weak association between religion and behavior is consistent with theory and empirical studies using similar measures – the anonymous pairing and grouping of the economic games may moderate individual-level effects of religion. Our research is a strong complement to the empirical literature because the three studies involved a large and diverse sample and used sensitive instruments that have been found to reliably measure prosocial behavior.

Female genital cutting is not a social coordination norm

New data from Sudan question an influential approach to reducing female genital cutting The World Health Organization defines female genital cutting as any procedure that removes or injures any part of a females external genitalia for nonmedical reasons (1). Cutting brings no documented health benefits and leads to serious health problems. Across six African countries, for example, a cohort of 15-year-old girls is expected to lose nearly 130,000 years of life because of cutting (2). We report data that question an influential approach to promoting abandonment of the practice.

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.