Paying Back People Who Harmed Us but Not People Who Helped Us: Direct Negative Reciprocity Precedes Direct Positive Reciprocity in Early Development.

The principle of direct reciprocity, or paying back specific individuals, is assumed to be a critical component of everyday social exchange and a key mechanism for the evolution of cooperation. Young children know the norm of reciprocity, but it is unclear whether they follow the norm for both positive and negative direct reciprocity or whether reciprocity is initially generalized. Across five experiments (N = 330), we showed that children between 4 and 8 years of age engaged in negative direct reciprocity but generalized positive reciprocity, despite recalling benefactors. Children did not endorse the norm of positive direct reciprocity as applying to them until about 7 years of age (Study 4), but a short social-norm training enhanced this behavior in younger children (Study 5). Results suggest that negative direct reciprocity develops early, whereas positive reciprocity becomes targeted to other specific individuals only as children learn and adopt social norms.

The evolution of self-control.

Cognition presents evolutionary research with one of its greatest challenges. Cognitive evolution has been explained at the proximate level by shifts in absolute and relative brain volume and at the ultimate level by differences in social and dietary complexity. However, no study has integrated the experimental and phylogenetic approach at the scale required to rigorously test these explanations. Instead, previous research has largely relied on various measures of brain size as proxies for cognitive abilities. We experimentally evaluated these major evolutionary explanations by quantitatively comparing the cognitive performance of 567 individuals representing 36 species on two problem-solving tasks measuring self-control. Phylogenetic analysis revealed that absolute brain volume best predicted performance across species and accounted for considerably more variance than brain volume controlling for body mass. This result corroborates recent advances in evolutionary neurobiology and illustrates the cognitive consequences of cortical reorganization through increases in brain volume. Within primates, dietary breadth but not social group size was a strong predictor of species differences in self-control. Our results implicate robust evolutionary relationships between dietary breadth, absolute brain volume, and self-control. These findings provide a significant first step toward quantifying the primate cognitive phenome and explaining the process of cognitive evolution.

Prospection and delay of gratification support the development of calculated reciprocity.

Humans frequently benefit others strategically to elicit future cooperation. While such forms of calculated reciprocity are powerful in eliciting cooperative behaviors even among self-interested agents, they depend on advanced cognitive and behavioral capacities such as prospection (representing and planning for future events) and extended delay of gratification. In fact, it has been proposed that these constraints help explain why calculated reciprocity exists in humans and is rare or even absent in other animals. The current study investigated the cognitive foundation of calculated reciprocity by examining its ontogenetic emergence in relation to key aspects of children's cognitive development. Three-to-five-year-old children from the US (N = 72, mostly White, from mixed socioeconomic backgrounds) first completed a cognitive test battery assessing the cognitive capacities hypothesized to be foundational for calculated reciprocity. In a second session, children participated in a calculated reciprocity task in which they could decide how many resources to share with a partner who later had the opportunity to reciprocate (reciprocity condition) and with a partner who could not reciprocate (control condition). Results indicated a steep developmental emergence of calculated reciprocity between 3 and 5 years of age. Further analyses showed that measures of delay of gratification and prospection were important predictors of children's rate of calculated reciprocity, even when controlling for age and after including a measure of verbal ability. By contrast, theory of mind abilities were unrelated to children's reciprocal behavior. This is the first systematic investigation of essential cognitive capacities for calculated reciprocity. We discuss prospection and delay of gratification as two domain-general capacities that are utilized for calculated reciprocity and which could explain developmental as well as species-differences in cooperation.

Disgusting Democrats and Repulsive Republicans: Members of Political Outgroups Are Considered Physically Gross.

The status of disgust as a sociomoral emotion is debated. We conducted a stringent test of whether social stimuli (specifically, political outgroup members) can elicit physical disgust, as distinct from moral or metaphorical disgust. We employed stimuli (male faces) matched on baseline disgustingness, provided other ways for participants to express negativity toward outgroup members, and used concrete self-report measures of disgust, as well as a nonverbal measure (participants' facial expressions). Across three preregistered studies (total N = 915), we found that political outgroup members are judged to be "disgusting," although this effect is generally weaker for concrete self-report measures and absent for the nonverbal measure. This suggests that social stimuli are capable of eliciting genuine physical disgust, although it is not always outwardly expressed, and the strength of this result depends on the measures employed. We discuss implications of these results for research on sociomoral emotions and American politics.

The developmental emergence of direct reciprocity and its influence on prosocial behavior.

Humans are a remarkably cooperative species, and one behavior thought to play an important role is that of reciprocal altruism. By ensuring that the immediate costs associated with performing a prosocial action will be recouped in the long-run, reciprocal interactions support the emergence and maintenance of group-level cooperation. Existing developmental research suggests that a tendency toward selective prosocial behavior and an understanding of direct reciprocal interactions emerge in early childhood, but much less is known about the interplay between these two behaviors. In this paper, I review the existing literature supporting the notion that reciprocity mediates early prosocial tendencies and suggest that a greater understanding of the psychological mechanisms underlying reciprocity is needed. Finally, I propose two social cognitive capacities related to prospection that I believe may help to shed light on the psychology of strategic reciprocal interactions and their role in prosocial behavior more broadly.

Give what you get: capuchin monkeys (Cebus apella) and 4-year-old children pay forward positive and negative outcomes to conspecifics.

The breadth of human generosity is unparalleled in the natural world, and much research has explored the mechanisms underlying and motivating human prosocial behavior. Recent work has focused on the spread of prosocial behavior within groups through paying-it-forward, a case of human prosociality in which a recipient of generosity pays a good deed forward to a third individual, rather than back to the original source of generosity. While research shows that human adults do indeed pay forward generosity, little is known about the origins of this behavior. Here, we show that both capuchin monkeys (Cebus apella) and 4-year-old children pay forward positive and negative outcomes in an identical testing paradigm. These results suggest that a cognitively simple mechanism present early in phylogeny and ontogeny leads to paying forward positive, as well as negative, outcomes.

Young children are more generous when others are aware of their actions.

Adults frequently employ reputation-enhancing strategies when engaging in prosocial acts, behaving more generously when their actions are likely to be witnessed by others and even more so when the extent of their generosity is made public. This study examined the developmental origins of sensitivity to cues associated with reputationally motivated prosociality by presenting five-year-olds with the option to provide one or four stickers to a familiar peer recipient at no cost to themselves. We systematically manipulated the recipient's knowledge of the actor's choices in two different ways: (1) occluding the recipient's view of both the actor and the allocation options and (2) presenting allocations in opaque containers whose contents were visible only to the actor. Children were consistently generous only when the recipient was fully aware of the donation options; in all cases in which the recipient was not aware of the donation options, children were strikingly ungenerous. These results demonstrate that five-year-olds exhibit "strategic prosociality," behaving differentially generous as a function of the amount of information available to the recipient about their actions. These findings suggest that long before they develop a rich understanding of the social significance of reputation or are conscious of complex strategic reasoning, children behave more generously when the details of their prosocial actions are available to others.