Fairness concerns are thought to guide resource allocation behavior toward mutually satisfactory outcomes, but behaving according to principles of fairness can be personally costly. The observation that humans are willing to engage in costly cooperative behavior, has led to a long-standing debate about why cooperation persists even when pitted against immediate self-interest (Tomasello and Vaish, 2013). A prominent approach that has been applied to understanding the cognitive processes that determine cooperative behavior is the dual-system model, which pits a fast intuitive system against a slow deliberate system as determinants of human decision making. While the dual system approach has gained traction as a leading theoretical model to account for cooperative decision making, there is considerable debate amongst dual system theorists about which system is dominant in cooperative decisions. One leading theoretical perspective suggests that humans are inherently selfish, but through deliberate, effortful control this tendency toward self-maximizing can be inhibited in favor of costly cooperative behaviors (Trivers, 1971; Stevens and Hauser, 2004). Alternative models propose that cooperation is intrinsically motivated (Batson and Shaw, 1991; Hoffman, 2000; Warneken and Tomasello, 2009), largely intuitive, and independent of effortful control (Rand et al., 2012; Zaki and Mitchell, 2013). Importantly, framing the question of the nature of cooperative decision making as originating from either intuitive or deliberate cognitive processes overlooks the fact that cooperation comes in many forms, and in all probability both processes are important determinants of cooperative behavior with the relative contribution varying considerably across cooperative types and contexts. As we begin to map the relative role of intuition and deliberation in cooperative decisions it is important to study their emergence and subsequent development to understand how these processes function in specific cooperative contexts, such as fairness behaviors, which are thought to play a fundamental role in the organization of human cooperative relations.

A well-established approach to assessing the contribution of intuitive and reflective decision processes on cooperative behavior is to examine the impact of decision time on cooperative behaviors. The dual-process model of decision making proposes that decisions arise from distinct cognitive systems: a fast, intuitive, or ‘hot’ system that is efficient but relies on heuristics and is susceptible to bias and predictable errors, contrasted with a slow, deliberate or ‘cold’ system that is more cognitively demanding but can be applied flexibly and rationally through deliberate control (Sloman, 1996; Gilovich et al., 2002; Kahneman, 2011; Greene, 2014; Corbit et al., 2023a). Importantly, the dual-process model is hotly debated within the behavioral sciences with some theorists supporting a single-process model where deliberate and intuitive decisions represent differences in degrees rather than qualitatively distinct systems (Kruglanski and Gigerenzer, 2018). Furthermore, others argue that forming a distinction between single- and dual-process models is intractable given current empirical evidence (De Neys, 2021). While the application of dual-process models of decision making remains a topic of debate there is substantial agreement that manipulating response time is an experimental approach that typically correlates to the two cognitive processes, with fast decisions more often recruiting an intuitive process and slow decisions more often relying on deliberate processes (Capraro, 2024).

Recently, a considerable literature has emerged that explores the relative contribution of intuitive and reflective processes on cooperative decisions. Several lines of converging evidence suggest that adults may be intuitive cooperators under specific contexts. For example, in public goods games, where adults must decide between outcomes that are self-maximizing or cooperating to provide a larger benefit to their group, decisions made under time pressure or those primed with intuitive thinking are more likely to be cooperative (Cappelletti et al., 2011; Cornelissen et al., 2011; Rand et al., 2012; but see Bouwmeester et al., 2017). Further, meta-analytic evidence suggests that intuitive cooperation is more likely to occur under pure cooperation conditions, where cooperation does not provide a personal benefit, and when it is unlikely to be exploited (Rand et al., 2014; Rand, 2016). In the ultimatum game, wherein participants can decide to accept or reject offers of resource and behavior closely maps to fairness preferences, a meta-analysis found that adults were more likely to reject unfair offers when intuitive decision processes were promoted (Capraro, 2024). Further, the effect of intuition on sharing decisions, as when allocating resources to a single passive recipient, may show less impact of intuitive decision processes according to recent meta-analyses that found no evidence for an impact on altruistic sharing from promoting intuitive or reflective decision processes (Fromell et al., 2020; Capraro, 2024). Together this this evidence suggests that amongst adults the impact of intuitive and reflective decision can vary considerably based on the type of cooperative decision and the context within which cooperative decisions are made.

Recently, researchers have begun to apply a dual-process model to study the development of cooperative decision making with mixed results. In one study, toddlers who were fast to provide help in response to an experimenter’s need showed a higher rate of helping over repeated trials compared to those who were slow to respond (Grossmann et al., 2020). For older children (3–7 years of age), sharing decisions that were made under time pressure tended to be more generous compared to decisions that were made after a 10-s delay (Plötner et al., 2021). Additionally, in a modified public goods game that gave children (7–12 years of age) a choice between 2 resources for themselves or 1 each for themselves and three group members (costly cooperation), children were more likely to cooperate when their decisions were made under time pressure compared to a 10-s time delay or a neutral condition where decision time was unconstrained (Corbit et al., 2023a). While these studies highlight an important role for intuitive cooperation throughout early to late childhood, another recent study reveals a different pattern when children are given a choice to share resources equally or give more to themselves. In this study children (4–9 years of age) were given a choice between an equal distribution of resources (2 each) or a selfish distribution (3 self, 1 recipient) and their decision times were recorded (Chajes et al., 2022). Young children (4–6 years of age) rarely chose the equal option, but when they did, these decisions were slower compared to the selfish ones. Older children (7–9 years of age) were more likely to choose the equal distribution, but in this case their decisions were not predicted by decision time (Chajes et al., 2022). Taken together, these findings suggest that from an early age children show a tendency toward intuitive cooperation across several cooperative contexts, but this pattern might not extend to costly fairness.

Based on the evidence reviewed thus far, the impact of intuitive decisions on the development of fairness is difficult to adjudicate due to methodological differences across previous studies examining children’s sharing decisions. For instance, while Plötner et al. (2021) found that time pressure increased generosity relative to a time delay, children in this study were given nine resources to distribute and so distributing equally was not an option. In the case of Chajes et al. (2022), children received the option of distributing resources equally, but equal decisions were also more generous as they gave the recipient 2 resources rather than 1 resource for the recipient if children chose the selfish option. Finally, Corbit et al. (2023a) found that for intuitive decisions children were more likely to give resources to their group, a decision that resulted in an equal distribution with each player receiving 1 resource, while selfish decisions resulted in an unequal distribution with the participant receiving 2 resources and the other players none. In this case cooperative decisions achieved equality but may have been aimed to ensure that the other players got something, rather than being governed by a strict preference for fairness. Thus, to clarify the impact of intuitive decisions on children’s specific concern for fairness it is important to employ a methodology that can adjudicate between a motivation to achieve fairness and other cooperative concerns, such as generosity.

A common method to assess children’s concern for fairness independently of generosity is to examine how they respond to unequal distributions of resources. Achieving fairness by discarding unequal distributions of resources demonstrates a concern for fairness that is non-generous, and so provides insight into fairness preferences that are distinct from generosity (Corbit et al., 2017). Avoidance of unequal distributions to achieve fairness has been described as an aversion to inequity (Fehr and Schmidt, 1999). Inequity aversion takes two forms; disadvantageous inequity aversion avoids receiving fewer resources than a peer, whereas advantageous inequity aversion avoids receiving more resources than a peer. When young children (4–6 years of age) are presented with fewer resources than a peer, they avoid this disadvantageous form of unfairness by rejecting those distributions, a pattern observed across societies (Blake et al., 2015). Remarkably, older children (~7–8 years of age) in some societies also reject unequal resource distributions that advantage them by giving them more than a peer (Blake et al., 2015; Paulus, 2015; Corbit et al., 2017; Kajanus et al., 2019; Li et al., 2022; Corbit et al., 2023b).

Advantageous and disadvantageous inequity aversion are likely supported by different cognitive processes. For instance, disadvantageous inequity aversion might be motivated by spite or envy toward an advantaged recipient (McAuliffe et al., 2011; Shaw and Olson, 2012) and may well represent a mild form of reactive aggression elicited by a negative emotional response to receiving less (Brosnan and de Waal, 2014). Advantageous inequity aversion signals a strong concern for other regarding fairness and may be motivated by avoiding negative social emotions, such as guilt or shame, and adherence to social norms (Blake et al., 2015; Gerdemann et al., 2022). Recent efforts to understand the cognitive mechanisms that produce children’s fairness decisions have found that distinct evaluative (Amir et al., 2023) and inhibitory (Sobel et al., 2024) processes underlie responses to advantageous and disadvantageous inequity. Importantly, although these studies have provided new insights about the cognitive factors that foster the development of fairness concerns, the role of intuitive and reflective decision processes on the development of inequity aversion remains an open question.

The primary goal of our study was to assess the relative influence of intuitive and reflective decision processes on the development of children’s fairness behavior. We were specifically interested in the impact of these decision processes on two forms of fairness, advantageous and disadvantageous inequity aversion. In both the Fast and Slow conditions children rejected unequal advantageous offers more often than equal offers beginning between 6 and 7 years of age, and this tendency increased with age. Importantly, we found that the age-related increase in advantageous inequity aversion was greater in the Fast condition relative to the Slow condition. This pattern provided partial support for H1; although the age of emergence was similar across Fast and Slow conditions, the age-related increase in advantageous inequity aversion was greater in the Fast condition compared to the Slow condition. We failed to find evidence for H2; that deliberate decisions would allow children to inhibit self-maximizing tendencies and increase costly fairness. On disadvantageous trials we did not find that decision time impacted children’s disadvantageous inequity aversion. In both the Fast and Slow conditions, children rejected unequal offers more often than equal ones from 5 years of age, a tendency that increased with age until around 8 years, at which point rejection of unequal offers began to decline. This pattern did not provide evidence in support of either an increase in generosity (H3) or reactive aggression (H4) stemming from intuitive decision processes. Thus, taken together our findings reveal that recruiting intuitive decision processes in fairness decisions may lead to a more robust expression of children’s tendency to reject resource distributions that give them a relative advantage over a peer.

To our knowledge this was the first study that directly tested the impact of intuitive and deliberate decision processes on the development of inequity aversion. There are several related studies that may appear to provide contradictory evidence, but which have important methodological differences. In one study, Chajes et al. (2022) presented children (4–9 years of age) with a forced choice sharing decision between an equal (2 resources each) or selfish (3 for self, 1 for recipient) distribution. Younger children (4–6 years of age) rarely chose the equal option (~20% of the time), but when they did, equal decisions tended to be slower compared to selfish decisions. However, decision time did not predict decisions for older children (7–9 years of age), who were more likely to choose the equal option (>60% of the time). Two methodological differences could account for the divergent pattern of results between the current study and Chajes et al. (2022). First, as noted in the introduction, fair decisions in the Chajes et al. (2022) paradigm were also generous because they increased the number of resources given to the recipient (2 as opposed to 1), whereas fair decisions in the current study were non-generous because rejecting unequal offers reduced the payoff for both the actor and recipient. Meta-analytic evidence from adults suggests that while altruistic giving was not positively impacted by intuitive relative to deliberative decision processes, the tendency to reject unfair offers in the ultimatum game was (Fromell et al., 2020; Capraro, 2024), which could provide some insight into the differences observed in the current study compared to those of Chajes et al. (2022). A second methodological difference relates to decision time. Decision time varied naturally in the Chajes et al. (2022) study, whereas decision time was experimentally manipulated to be under time pressure (Fast conditions) or after a 10-s delay (Slow conditions) in the current study. It is possible that experimentally manipulating decision time in the current procedure may have increased the impact of decision time on fairness preferences compared to procedures where decision time varies naturally across cooperative decisions. Indeed, it has been proposed that correlational designs, where response time varies naturally, correspond to decision conflict rather than intuitive or deliberate decision processes (Evans and Rand, 2019). It is also worth noting that previous studies that have revealed evidence for intuitive cooperation in children’s resource allocation decisions manipulated decision time (Plötner et al., 2021; Corbit et al., 2023a), whereas those that did not find evidence for an intuitive effect allowed decision times to vary naturally (Blake and McAuliffe, 2011; Chajes et al., 2022). The role of intuitive decisions in the development of cooperative behaviors is a relatively new area of empirical inquiry and so more evidence is needed before firm conclusions can be made, especially studies that attempt to replicate the effects and meta-analyses when sufficient data is available (see Rand, 2016; Bouwmeester et al., 2017; Fromell et al., 2020; Capraro, 2024).

An additional methodological feature of the current study that might have impacted our results is that children’s decisions were made on a tablet where the distribution of candies were represented symbolically as cartoon skittles. Although real Skittles were distributed on every trial that participants accepted an offer, it is possible that symbolic distancing affected decisions on the tablet compared to the apparatus employed in previous studies (e.g., Blake et al., 2015). In a study using the classic ‘less is more’ task, which requires pointing to a smaller reward in order to receive a larger reward, 3-year-old children’s performance improved significantly when the rewards were symbolic representations of candies compared to real candies (Carlson et al., 2005). These findings were interpreted to suggest that inhibiting the desire to point to a larger, more enticing, reward was easier when the rewards were represented symbolically. However, studies that have examined the impact of symbolic distancing on fairness decisions have produced mixed results. Ebersbach et al. (2022) found that children (4–6 years old) were more likely to reject unequal offers when they were represented symbolically (tokens vs. stickers). In contrast, Ahl et al. (2023) found that children were less likely to reject advantageous offers in a token-based online compared to an in-person real candy version of the inequity game. If symbolic distancing reduced the inhibitory demands of rejecting unequal distributions in the inequity game in the current study, it would be more likely that reduced inhibitory demands would wash out any benefit from employing reflective decision processes, rather than enhance the benefit of intuitive decisions. Thus, it is unlikely that symbolic distancing can account for increased fairness decisions under intuitive conditions in the current study. Nevertheless, additional research is needed to tease apart the potential role of symbolic distancing on the relative impact of intuitive and reflective decision processes on costly cooperative behavior.

This is the first study to examine the impact of intuitive and reflective decision processes on children’s aversion to advantageous and disadvantageous inequity. We found that fast, intuitive decisions led to a greater age-related increase of advantageous inequity aversion compared to decisions made after a time delay. In contrast, we did not find evidence that disadvantageous inequity aversion was impacted by decision time. These findings suggest that recruiting intuitive decision processes might strengthen the emergence of advantageous inequity aversion during middle childhood.

The datasets presented in this study can be found in online repositories. The names of the repository/repositories and accession number(s) can be found at: https://osf.io/7g6mp/?view_only=6cf39cb2da9d498bacb221352d7392b1.

The studies involving humans were approved by the Research Ethics Board at St Francis Xavier University. The studies were conducted in accordance with the local legislation and institutional requirements. Written informed consent for participation in this study was provided by the participants’ legal guardians/next of kin.

JC: Writing – review & editing, Writing – original draft, Visualization, Validation, Supervision, Software, Resources, Project administration, Methodology, Investigation, Funding acquisition, Formal analysis, Data curation, Conceptualization.