Katherine McAuliffe

“I had so much it didn’t seem fair”: Eight-year-olds reject two forms of inequity

Research using economic games has demonstrated that adults are willing to sacrifice rewards in order to prevent inequity both when they receive less than a social partner (disadvantageous inequity) and when they receive more (advantageous inequity). We investigated the development of both forms of inequity aversion in 4- to 8-year-olds using a novel economic game in which children could accept or reject unequal allocations of candy with an unfamiliar peer. The results showed that 4- to 7-year-olds rejected disadvantageous offers, but accepted advantageous offers. By contrast, 8-year-olds rejected both forms of inequity. These results suggest that two distinct mechanisms underlie the development of the two forms of inequity aversion.

Female Mate Choice in Mammals

Studies of mate choice in vertebrates have focused principally on birds, in which male ornaments are often highly developed, and have shown that females commonly select mates on the basis of particular phenotypic characteristics that may reflect their genetic quality. Studies of female mate choice in mammals are less highly developed, and they have commonly focused on female mating preferences that are likely to be maintained by benefits to the females own survival or breeding success. However, recent experimental studies of mate choice in mammals—especially rodents—provide increasing evidence of consistent female preferences that appear likely to generate benefits to the fitness of offspring. As yet, there is no compelling evidence that female mating preferences are less highly developed in female mammals than in female birds, although these preferences may more often be masked by the effects of male competition or of attempts by males to constrain female choice.

The ontogeny of fairness in seven societies

A sense of fairness plays a critical role in supporting human cooperation. Adult norms of fair resource sharing vary widely across societies, suggesting that culture shapes the acquisition of fairness behaviour during childhood. Here we examine how fairness behaviour develops in children from seven diverse societies, testing children from 4 to 15 years of age (n = 866 pairs) in a standardized resource decision task. We measured two key aspects of fairness decisions: disadvantageous inequity aversion (peer receives more than self) and advantageous inequity aversion (self receives more than a peer). We show that disadvantageous inequity aversion emerged across all populations by middle childhood. By contrast, advantageous inequity aversion was more variable, emerging in three populations and only later in development. We discuss these findings in relation to questions about the universality and cultural specificity of human fairness.

Costly third-party punishment in young children

Human adults engage in costly third-party punishment of unfair behavior, but the developmental origins of this behavior are unknown. Here we investigate costly third-party punishment in 5- and 6-year-old children. Participants were asked to accept (enact) or reject (punish) proposed allocations of resources between a pair of absent, anonymous children. In addition, we manipulated whether subjects had to pay a cost to punish proposed allocations. Experiment 1 showed that 6-year-olds (but not 5-year-olds) punished unfair proposals more than fair proposals. However, children punished less when doing so was personally costly. Thus, while sensitive to cost, they were willing to sacrifice resources to intervene against unfairness. Experiment 2 showed that 6-year-olds were less sensitive to unequal allocations when they resulted from selfishness than generosity. These findings show that costly third-party punishment of unfair behavior is present in young children, suggesting that from early in development children show a sophisticated capacity to promote fair behavior.

Development of in-group favoritism in children’s third-party punishment of selfishness

Significance Humans are unique among animals in their willingness to cooperate with friends and strangers. Costly punishment of unfair behavior is thought to play a key role in promoting cooperation by deterring selfishness. Importantly, adults sometimes show in-group favoritism in their punishment. To our knowledge, our study is the first to document this bias in children. Furthermore, our results suggest that from its emergence in development, children’s costly punishment shows in-group favoritism, highlighting that group membership provides critical context for understanding the enforcement of fairness norms. However, 8-y-old children show attenuated bias relative to 6-y-olds, perhaps reflecting a motivation for impartially. Our findings thus demonstrate that in-group favoritism has an important influence on human fairness and morality, but can be partially overcome with age. When enforcing norms for cooperative behavior, human adults sometimes exhibit in-group bias. For example, third-party observers punish selfish behaviors committed by out-group members more harshly than similar behaviors committed by in-group members. Although evidence suggests that children begin to systematically punish selfish behavior around the age of 6 y, the development of in-group bias in their punishment remains unknown. Do children start off enforcing fairness norms impartially, or is norm enforcement biased from its emergence? How does bias change over development? Here, we created novel social groups in the laboratory and gave 6- and 8-year-olds the opportunity to engage in costly third-party punishment of selfish sharing behavior. We found that by age 6, punishment was already biased: Selfish resource allocations received more punishment when they were proposed by out-group members and when they disadvantaged in-group members. We also found that although costly punishment increased between ages 6 and 8, bias in punishment partially decreased. Although 8-y-olds also punished selfish out-group members more harshly, they were equally likely to punish on behalf of disadvantaged in-group and out-group members, perhaps reflecting efforts to enforce norms impartially. Taken together, our results suggest that norm enforcement is biased from its emergence, but that this bias can be partially overcome through developmental change.

The developmental origins of fairness: the knowledge–behavior gap

Recent research in developmental psychology shows that children understand several principles of fairness by 3 years of age, much earlier than previously believed. However, childrens knowledge of fairness does not always align with their behavior, and immediate self-interest alone cannot explain this gap. In this forum paper, we consider two factors that influence the relation between fairness knowledge and behavior: relative advantage and how rewards are acquired.

Evolving the ingredients for reciprocity and spite

Darwin never provided a satisfactory account of altruism, but posed the problem beautifully in light of the logic of natural selection. Hamilton and Williams delivered the necessary satisfaction by appealing to kinship, and Trivers showed that kinship was not necessary as long as the originally altruistic act was conditionally reciprocated. From the late 1970s to the present, the kinship theories in particular have been supported by considerable empirical data and elaborated to explore a number of other social interactions such as cooperation, selfishness and punishment, giving us what is now a rich description of the nature of social relationships among organisms. There are, however, two forms of theoretically possible social interactions—reciprocity and spite—that appear absent or nearly so in non-human vertebrates, despite considerable research efforts on a wide diversity of species. We suggest that the rather weak comparative evidence for these interactions is predicted once we consider the requisite socioecological pressures and psychological mechanisms. That is, a consideration of ultimate demands and proximate prerequisites leads to the prediction that reciprocity and spite should be rare in non-human animals, and common in humans. In particular, reciprocity and spite evolved in humans because of adaptive demands on cooperation among unrelated individuals living in large groups, and the integrative capacities of inequity detection, future-oriented decision-making and inhibitory control.

Social influences on inequity aversion in children.

Adults and children are willing to sacrifice personal gain to avoid both disadvantageous and advantageous inequity. These two forms of inequity aversion follow different developmental trajectories, with disadvantageous inequity aversion emerging around 4 years and advantageous inequity aversion emerging around 8 years. Although inequity aversion is assumed to be specific to situations where resources are distributed among individuals, the role of social context has not been tested in children. Here, we investigated the influence of two aspects of social context on inequity aversion in 4- to 9-year-old children: (1) the role of the experimenter distributing rewards and (2) the presence of a peer with whom rewards could be shared. Experiment 1 showed that children rejected inequity at the same rate, regardless of whether the experimenter had control over reward allocations. This indicates that children’s decisions are based upon reward allocations between themselves and a peer and are not attempts to elicit more favorable distributions from the experimenter. Experiment 2 compared rejections of unequal reward allocations in children interacting with or without a peer partner. When faced with a disadvantageous distribution, children frequently rejected a smaller reward when a larger reward was visible, even if no partner would obtain the larger reward. This suggests that nonsocial factors partly explain disadvantageous inequity rejections. However, rejections of disadvantageous distributions were higher when the larger amount would go to a peer, indicating that social context enhances disadvantageous inequity aversion. By contrast, children rejected advantageous distributions almost exclusively in the social context. Therefore, advantageous inequity aversion appears to be genuinely social, highlighting its potential relevance for the development of fairness concerns. By comparing social and nonsocial factors, this study provides a detailed picture of the expression of inequity aversion in human ontogeny and raises questions about the function and evolution of inequity aversion in humans.

Human punishment is motivated by inequity aversion, not a desire for reciprocity

Humans involved in cooperative interactions willingly pay a cost to punish cheats. However, the proximate motives underpinning punitive behaviour are currently debated. Individuals who interact with cheats experience losses, but they also experience lower payoffs than the cheating partner. Thus, the negative emotions that trigger punishment may stem from a desire to reciprocate losses or from inequity aversion. Previous studies have not disentangled these possibilities. Here, we use an experimental approach to ask whether punishment is motivated by inequity aversion or by a desire for reciprocity. We show that humans punish cheats only when cheating produces disadvantageous inequity, while there is no evidence for reciprocity. This finding challenges the notion that punishment is motivated by a simple desire to reciprocally harm cheats and shows that victims compare their own payoffs with those of partners when making punishment decisions.

Are cleaner fish, Labroides dimidiatus, inequity averse?

Inequity aversion (IA), a willingness to incur temporary costs to prevent unequal outcomes, is common in humans and thought to be beneficial in the context of cooperative relationships with nonkin, since it might allow individuals to regulate contributions to cooperative activities. Attempts to address whether nonhuman animals also show IA have produced mixed results: some studies found that cooperative species are more likely to show IA while others did not. This ambiguity may arise because animals are typically tested for an aversion to working for differential food rewards, even though most tested species do not regularly cooperate to access food. We used the interspecific mutualism between cleaner fish and their reef-fish ‘clients’ to investigate whether IA exists in a species that regularly cooperates with unrelated individuals in the food domain. Cleaners were tested in pairs of actors and recipients. Actors had to perform a task to provide a food reward to both actor and recipient. Cleaners show consistent food preferences in the wild and under laboratory conditions, allowing us to vary the value of the food reward offered to actor and recipient to test whether actors were less likely to work when recipients received higher value rewards. We performed two experiments: actors worked either for their opposite-sex partner or for a same-sex competitor. We found no evidence that cleaners were sensitive to inequity: actors were equally likely to perform the task in all experimental conditions. We discuss these results in light of theories of the evolution of IA.