Infants' expectations about resource distributions in a sharing situation

Introduction

There has been increasing interest in the emergence of early socio-moral understanding in the past two decades. Extensive studies have demonstrated that infants and toddlers show sensitivity to morally-related behaviors (see Woo et al., 2022, for a review). One line of such research has provided converging evidence that infants show a sense of fairness. Specifically, previous studies have found that infants' fairness considerations emerge in their first year of life (e.g., Buyukozer Dawkins et al., 2019; Ziv and Sommerville, 2017) and become more stable in their second year (e.g., Schmidt and Sommerville, 2011; Sloane et al., 2012). Overall, these studies have found that infants as young as 4 months old expect a distributor to allocate resources equally to two recipients.

The current literature shows that infants' sensitivity to fairness in resource allocation is multifaceted, encompassing various experimental methodologies. Studies using violation-of-expectation paradigms demonstrated that infants detect violations of fairness norms (e.g., Meristo et al., 2016; Sloane et al., 2012; Ziv and Sommerville, 2017). Specifically, infants looked longer at scenes depicting unequal than equal resource distributions. In addition, infants preferred fair distributors to unfair distributors as pronounced by their preferential looking and manual choices (e.g., Burns and Sommerville, 2014; Lucca et al., 2018). For instance, in one study, 13- and 17-month-olds infants were more likely to choose to interact with a fair distributor than an unfair distributor (Lucca et al., 2018). However, infants' preference for fair distributors may not yet reflect an explicit, language-based moral evaluation of fairness. Although 20-month-olds preferred a fair distributor in a simple choice task, neither 20–30-month-olds reliably selected the fair distributor when the task required them to map the evaluative word “good” onto one of the distributors (Franchin et al., 2019).

Beyond simply distinguishing between fair and unfair distributors, infants' sensitivity to fairness guides broader social evaluations and expectations about how others should respond to these agents. For example, infants expect punishment for unfair agents and rewards for fair agents in the context of resource distributions (e.g., DesChamps et al., 2016; Geraci and Surian, 2023; Meristo and Surian, 2014). Their own behavior also reflects such evaluations. Infants selectively help fair rather than unfair agents, suggesting that fairness information influences not only their attention and expectations but also their social actions (Surian and Franchin, 2017a). Moreover, infants' fairness judgments are not based solely on numerical equality. They also take into account contextual information relevant to whether an allocation is justified, including recipients' deservingness, prior actions, and merit (e.g., Surian and Franchin, 2017b). Together, these findings suggest that infants' sensitivity to fairness involves an emerging capacity to evaluate distributive actions in relation to both social consequences and contextual considerations.

The findings regarding infants' differentiation between fair and unfair resource distributions are consistent with the previous research conducted with older children and adults. As children grow older, they increasingly show inequality aversion and/or preference toward equality when they are asked to share resources between themselves and others (e.g., Fehr et al., 2008). For instance, children as young as 3 years responded negatively to unequal resource allocation and actually shared resources equally between themselves and other individuals who had collaborated with them (e.g., LoBue et al., 2011; Warneken et al., 2011). Therefore, infants' sensitivity to inequality may be a precursor to the norm-guided concern for fairness and egalitarianism presented later in life.

The early sense of fairness does not operate in isolation. Theoretically and empirically, infants' fairness considerations are linked to their propensity to prosociality (Sommerville, 2018). Previous research has found that infants' sense of fairness is linked to their own sharing behavior. For example, 9-month-olds' naturalistic sharing (i.e., sharing that occurs spontaneously in everyday life) predicted whether an infant detected unfairness in resource allocation (Ziv and Sommerville, 2017). In addition, 15-month-olds' willingness to engage in altruistic sharing was linked to their visual attention to unfair distributive outcomes (Sommerville et al., 2013). These studies suggest that infants' prosocial actions, particularly sharing, may serve as a building block for their understanding of fairness norms, and their fairness sensitivity may be linked to their other-regarding concerns.

However, despite the close link between infants' expectation of equal resource distributions and their sharing behaviors, the current literature does not provide clear evidence regarding whether and how infants react to (un)fair resource allocation in the context of sharing. To our knowledge, most of the previous studies regarding infants' fairness sensitivity examined the distributive situations in which a distributor allocates resources to two other individuals (i.e., a 3rd-party allocation). Little research so far has investigated infants' concerns for fairness in a 1st-party resource allocation in which an agent shares his/her own resources with their partner. Unlike a 3rd-party allocation, the sharing context always involves a cost to a sharer. Thus, a distributor's action always influences their own wellbeing. It is unknown whether infants recognize this difference (i.e., cost of sharing) in processing events related to resource allocations or whether they merely employ the equality norms to resource allocation settings in general. Given the age gaps between the emergence of fairness consideration (i.e., 1st and 2nd year of life) and stable presentations of selfless sharing behavior during childhood (i.e., 3-years of age in some studies, but 7- or 8-years of age in others; Fehr et al., 2008; LoBue et al., 2011; Warneken et al., 2011), identifying early distributive concerns toward sharing behavior will shed light on the direction for early intervention for moral development (Geraci et al., 2023).

Therefore, the current study aims to investigate whether infants in their second life expect resources to be distributed equally, even in a first-party sharing situation where a distributor shares resources between themselves and their partner. Using a violation-of–expectation paradigm, we presented 14–19-month-olds with live events in which an individual shared resources either equally or unequally with another individual, and then analyzed infants' looking times during the events. In Experiment 1, infants were randomly assigned either to the Experimental or Control condition. Those in the Experimental condition watched fair and unfair resource allocations in a sharing context in which a distributor shared resources by moving them from their own tray to their partner's. Those in the Control condition watched the scenes that presented the same action (i.e., moving resources to another tray) but did not include a social component, as there was no recipient, but only one actor was present. The purpose of the Control condition was to test the possibility that infants' detection of unfair allocations in Experiment 1, if any, was not due to their expectation of perceptual symmetry of object placement. We also conducted Experiment 2 in order to investigate whether infants differentiate equal sharing from resource allocation that made inequality but an altruistic outcome toward the recipient (i.e., allocating more resources to a recipient than to themselves). Fourteen- to 19-month-olds were selected as the sample, as previous studies demonstrated that infants in these ages showed more stable detection of unfair resource distributions compared to younger infants (e.g., Ziv and Sommerville, 2017) and that their fairness considerations were linked to their sharing behavior (e.g., Schmidt and Sommerville, 2011; Sommerville et al., 2013).

Experiment 1

Method

Sample

The participants were 46 infants aged 14–19-months (M age = 16 months and 25 days, range = 14 months and 0 days to 19 months and 25 days; 23 boys). Twenty-six additional infants participated but were excluded from the analyses because participants were fussy/crying/distracted (N = 9), infants did not finish either or both of the test trials (N = 4), operational or technical errors occurred during the experiment (N = 4), participants were older than 19-month-olds (N = 3), and they did not look at the scene at least for 5 s during either or both of the test trials (N = 6). Participants were recruited from a metropolitan area of South Korea through advertisements in online parenting communities.

Participants were randomly assigned either to the Experimental or the Control condition. There were 22 infants in the Experimental condition (M age = 16 months and 24 days, range = 14 months and 6 days to 19 months and 25 days; 10 boys) and 24 in the Control condition (M age = 16 months and 26 days, range = 14 months and 0 days to 19 months and 8 days; 13 boys).

We conducted a sensitivity power analysis using G^*Power (Faul et al., 2007) to evaluate robustness of the Event X Condition interaction effect. Given our sample size (N = 46), α = 0.05, power (1-β) = 0.80, and the observed correlation between repeated measures (r = 0.26), the sample size of 46 was determined to be sufficient to detect a minimum critical effect size of f = 0.257 (equivalent to ηp2 = 0.062).

Stimuli and procedure

The experiment was conducted in a quiet lab space at a university. After warming up, infants and their caregivers entered the lab space, which was equipped with an apparatus consisting of a live event stage and two side wings. During the experiment, infants were sitting on their caregiver's lap, approximately 60 cm apart from the center of the apparatus. Infants watched a series of live events during which caregivers were instructed to close their eyes and avoid interacting with their child. In both the Experimental and Control conditions, the live events consisted of one familiarization trial followed by two test trials.

Experimental condition

The purpose of the experimental condition was to investigate whether infants expect a distributor to share their own resources equally with a recipient (see Figure 1).

Infants first saw one familiarization event in which two actors (1 sharer, 1 recipient) sat side by side with a rectangular-shaped tray in front of each of them. We chose red cubes as the resource, following previous studies that used neutral objects such as disks in studying infants' expectations about resource distribution (e.g., Geraci and Surian, 2011). To highlight the cubes as possessable resources, each actor was presented with a plate, and the cubes were placed on the plates, thereby emphasizing ownership and the transfer of goods. Actor 1 on the right side of the stage (from the infants' point of view) wore a red shirt and had six red cubes on her tray, whereas Actor 2 (in a blue shirt) did not have any cubes on her tray. Both of the actors were staring at their own trays during the entire event without making any remarks.

Following the familiarization, all participants watched two live test events (one equal test event and one unequal test event). The order of the test events was counterbalanced.

During the equal test event, Actor 1 (sharer) allocated 3 out of 6 cubes to Actor 2 (recipient). Upon the start of the trial, both Actor 1 and Actor 2 were looking at Actor 1′s tray. After 1 s from the onset, Actor 2 said “wow” while staring at Actor 1′s tray. Then, 1 s later, Actor 1 grasped the first object with her right hand and then placed it onto Actor 2′s tray. Both Actor 1′s and Actor 2′s eyes followed the first object as it moved, and Actor 2′s gaze was fixed on her own tray afterwards. Then, Actor 1 moved the second and the third cubes to Actor 2′s tray one by one, while her gaze followed each object. Each allocation lasted 2 s.

During the unequal test event, Actor 1 shared only one out of six cubes with Actor 2. The event started with a scene in which both Actor 1 and Actor 2 were looking at Actor 1′s tray. One second into the trial, Actor 2 said “wow” while gazing at Actor 1′s tray. Following an additional 6-s pause, Actor 1 picked up one cube from her tray and placed it in Actor 2′s tray, taking 2 s for the movement. Both Actor 1 and Actor 2 visually tracked the movement of the object. The total length of equal and unequal test events was 12 s each.

Control condition

The Control condition was conducted to investigate whether infants expect objects to be placed symmetrically on the two trays. The procedure of the Control condition was similar to that of the Experimental condition, except that there was only one Actor. That is, no resource allocation between two individuals was made in the test trials. Instead, an individual moved cubes from one tray to another (see Figure 2).

Throughout the Familiarization event, only one actor (wearing a red shirt) was present. Six cubes were on the right tray (from the infants' point of view), whereas the left tray was empty. The actor's eyes were fixed on the tray with 6 cubes.

All participants watched two test events, and the order of the events was counterbalanced. During the symmetry test event, the actor moved 3 out of 6 cubes from one tray to another. The event started with a scene in which the actor looked at the tray with 6 cubes. Upon the 1 s of the trial, the actor said “wow” while staring at the cubes. After another second, the actor picked up the first object with her right hand and then moved it to the left tray. The second and the third cubes were then moved to the left tray sequentially. The actor's eyes were following the cubes as they were moved. Each movement lasted 2 s.

During the asymmetry test event, the actor moved only one out of six cubes from one tray to another. First, the actor in a red shirt was staring at the tray with 6 cubes. After 1 s from the onset, the actor said “wow” while gazing at the cubes. Six seconds later, the actor grasped one cube and placed it onto the left tray. This movement took 2 s. The actor's gaze was fixed on the cube while it was moved. The total length of the symmetry and asymmetry test events was 12 s each.

Measuring looking times

Infants' looking times during the events were measured by two observers who were blind to the conditions. Each observer monitored infants' looking behavior through a peephole concealed on either side of the wings. The observers recorded infants' looking times by pressing a computer-linked button upon the infants' gaze toward the stage. Manual coding of infant looking times is a widely used and validated method in developmental research (e.g., Baillargeon et al., 1985; Baillargeon, 2004; Sloane et al., 2012). All events were terminated if infants looked away for 2 consecutive seconds or if a maximum duration of 60 s was reached. Only the looking times measured by the primary observer were included for analyses, and the second observer's records were used to measure reliability. The averaged reliability between the two observers was 92% in the Experimental condition (92, 94, and 91% in familiarization, 1^st test trial, and 2^nd test trial, respectively) and 90% in the Control condition (89, 90, and 91% in familiarization, 1^st test trial, and 2^nd test trial, respectively).

Results and discussion

Preliminary analyses showed that there were no effects of participants' gender and the order of the test events (Equal first vs. Unequal first) on infants' looking time during the test events, Fs (1, 44) < 0.24, ps > 0.63. Therefore, these two variables were not included in the main analyses.

To examine the outcomes of the violation-of-expectation paradigm, we employed a 2 (Event: Equal vs. Unequal) X 2 (Condition: Experimental vs. Control) repeated-measures ANOVA (analysis of variance), with Condition as a between-subject variable and Event as a within-subject variable (see Figure 3). There was no significant main effect of Event or Condition, Fs (1, 44) < 2.55, ps > 0.12, but we found a significant interaction between Event and Condition, F (1, 44) = 4.33, p = 0.04, ηp2 = 0.09. Follow-up pairwise comparisons with Bonferroni adjustment revealed that infants looked reliably longer at the unequal test event (M = 33.27, SD = 16.46) than the equal test event (M = 23.98, SD = 18.61), in the Experimental condition, p = 0.02. However, there was no difference in infants' looking times for the equal (M = 23.86, SD = 13.60) and unequal test events (M = 22.03, SD = 10.99) in the Control condition, p = 0.62.

The longer looking times during the unequal event compared to the equal event in the Experimental condition found in this VOE task demonstrated that infants aged 14–19 months expect an individual to share an equal amount of resources between themselves and another individual. Furthermore, the results of the Control condition ruled out the possibility that infants in the Experiments condition simply expected the perceptual symmetry of the objects displayed on the two trays. When the actor in the Control condition made the movements that were the same as those of the sharer in the Experimental condition but were different in that there was no recipient, the infants no longer expected an equal number of resources to be placed on both trays. This result is in line with the numerous previous studies showing that infants expect and prefer equal resource distribution among two individuals (e.g., Geraci and Surian, 2011; Meristo et al., 2016; Schmidt and Sommerville, 2011), but further suggests that infants in their second year of life hold expectations of the equal division of resources not only in third-party allocation situations but also in first-party sharing contexts where an agent shares their own resources.

However, given the nature of the sharing context examined in this study, it is unclear whether the result merely reflected infants' consideration of equal distributive norms as found in the previous study or whether the result demonstrated infants' expectation of prosocial, altruistic acts that involve benefitting other individuals. It is also possible that infants in this study may expect an individual to be more selfless by sharing more resources with another individual (sharing 1 resource vs. sharing 3 resources). To test these possibilities, we conducted Experiment 2 to figure out whether infants differentiate another type of unequal distribution that creates the same ratio between allocated resources (i.e., 1:5), but this time, it is more altruistic as more resources were given to the recipient (i.e., the sharer gets only one while giving out 5 resources out of 6).

Experiment 2

Method

Sample

The sample consisted of 27 infants aged 14–19-months (M age = 17 months and 0 days, range = 14 months and 3 days to 19 months and 21 days; 14 boys). Participants were recruited from a metropolitan area of South Korea through advertisements in online parenting communities. Four additional infants were tested but excluded from the sample due to technical/experimental errors.

The results from 27 infants in Experiment 2 were compared to those from 22 infants in the Experimental condition of Experiment 1. We conducted a sensitivity power analysis using G^*Power (Faul et al., 2007) to evaluate robustness of the Event X Experiment interaction effect among in total of 49 infants. Given our sample size (N = 49), α = 0.05, power (1-β) = 0.80, and the observed correlation between repeated measures (r = 0.18), the sample size of 49 was determined to be sufficient to detect a minimum critical effect size of f = 0.262 (equivalent to ηp2 = 0.064).

Stimuli and procedure

The experiment was also conducted in a quiet lab space as in Experiment 1, and the procedure was similar except that the unequal-altruistic test event was conducted instead of the unequal test event. Participants in Experiment 2 also received live events consisting of one familiarization trial followed by two test trials. The order of test trials was counterbalanced.

The familiarization event was conducted exactly the same as in the Experimental condition of Experiment 1. As in Experiment 1, Actor 1 (sharer) allocated 3 out of 6 cubes to Actor 2 during the equal test event, but in Experiment 2, the first cube was moved 6 seconds after Actor 1′s utterance (“wow!”). This change was made in order to make the lengths of the two test trials equal. The total length of the two test events was 16 seconds each, as 5 out of 6 cubes were allocated to Actor 2′s tray in the unequal-altruistic test event. The unequal-altruistic event started with a scene in which both Actor 1 and Actor 2 were looking at Actor 1′s tray. One second into the trial, Actor 2 said “wow” while staring at Actor 1′s tray. After another second, Actor 1 picked up one cube from her tray and moved it to Actor 2′s tray. Then, Actor 1 moved 4 more cubes to Actor 2′s tray one at a time. Each allocation took 2 s (see Figure 4).

The infants' looking times were measured in the same manner as in Experiment 1. The averaged reliability between the two observers was 91% (90, 91, and 93% in familiarization, 1^st test trial, and 2^nd test trial, respectively).

Results and discussion

Preliminary analyses were conducted to examine the effects of participants' gender and the order of the test events (Equal first vs. Unequal-Altruistic first). As there were no effects of gender and the order on infants' looking times during the test events, Fs (1, 25) < 0.90, ps > 0.35, these variables were excluded from the main analyses.

We compared the result of Experiment 2 with that of the Experimental condition of Experiment 1 by using a 2 (Event: Equal vs. Unequal) X 2 (Experiment: Experiment 1 vs. Experiment 2) repeated-measures ANOVA (analysis of variance), with Experiment as a between-subject variable and Event as a within-subject variable (see Figure 5). We found a significant interaction between Event and Experiment, F (1, 47) = 5.56, p = 0.02, ηp2 = 0.11. Follow-up pairwise comparisons with Bonferroni adjustment showed that, unlike the result of the Experimental condition of Experiment 1, there was no significant difference between infants' looking times during the equal test event (M = 28.86, SD = 16.06) and unequal-altruistic test event (M = 24.00, SD = 16.33) in Experiment 2, p = 0.23. This suggests that infants in Experiment 2 were no longer likely to expect resources to be shared equally than to be unequally. An additional Bonferroni corrected adjustment showed that infants' looking times during the equal events did not significantly differ between Experiments 1 and 2, p = 0.33, nor did they during the unequal events, p = 0.06.

The results of Experiment 2 showed that 14–19-month-olds did not differentiate the equal from unequal but altruistic resource allocations in a sharing context. That is, infants did not detect a violation when they compared an action resulting in an equal number of resources among two individuals to a sharing behavior providing more resources to the recipient than the distributor. Due to the null result, we cannot conclude whether infants in their second year hold specific expectations about altruistic sharing as they do of equal sharing. However, combined results from Experiments 1 and 2 suggest that infants selectively treated the selfish unequal outcome (i.e., the unequal event in the Experimental condition of Experiment 1) as a violation, but not necessarily the altruistic, selfless outcome (i.e., the unequal-altruistic event in Experiment 2), even when the numerical ratio of resource allocations remains identical. Although it was not significant, the tendency for infants to look at the unequal-selfish event in Experiment 1 longer than the unequal-altruistic event in Experiment 2 raises the possibility that infants may distinguish between selfish and altruistic forms of inequality. Future research with larger samples will be needed to determine the robustness of this pattern.

General discussion

The current study examined whether infants expect individuals to share resources fairly in first-party sharing contexts in which the distributor's own interests are directly involved. Across two experiments, we examined how 14–19-month-old infants responded to equal, selfish-unequal, and altruistic-unequal resource allocations. The findings suggest that infants' expectations in sharing contexts may extend beyond simple sensitivity to numerical equality and instead reflect early expectations regarding fair vs. selfish behavior.

When presented with the scenes in which a distributor allocated resources equally and unequally between themselves and their partner in Experiment 1, 14- to 19-month-olds expected an equal division of resources between individuals, even when such allocation is costly to the distributor. Our result corroborates the previous evidence showing that infants possess fairness expectations in third-party resource allocation. Extensive research has demonstrated that infants' detection of unfairness in resource allocation emerges in the first year of life and is solidified during the second year (Buyukozer Dawkins et al., 2019; Ziv and Sommerville, 2017). Therefore, our findings suggest that 14–19-month-olds are already equipped with the capacity to generalize their expectations of equal resource distribution from third-party distribution to sharing situations involving the distributor's own self-interest.

The results from the Control condition of Experiment 1 further suggest that infants did not merely detect visual asymmetry, but rather, they have a rudimentary understanding of fairness in social interactions. Specifically, when we remove the social component from the scenes by presenting only one individual acting exactly the same as in the Experimental condition, infants aged 14–19-months did not differentiate the test events. Thus, the results from Experiment 1 as a whole indicate that infants at these ages have an implicit understanding of how resources should be shared between two individuals (Sommerville and Enright, 2018).

Furthermore, our findings in Experiment 2 suggest that infants may not have simply responded to the violation of the equality norm but rather have reacted based on the underlying expectations of prosociality. When presented with the equal sharing event and altruistic sharing event, which created the same numerical inequality of resources as in the unequal event in Experiment 1, but in favor of the recipient, infants did not discriminate between the two test events as assessed by their looking times. This result implies that infants may consider both equal and altruistic sharing presented in Experiment 2 acceptable or prosocial, while categorizing the unequal sharing observed in Experiment 1 as violating prosocial norms. Previous studies showed that, when evaluating third-party resource distribution, infants would show sensitivity to principles of equality. However, our study revealed that when observing 1st-party resource allocation in which an individual shares their own resources with a recipient, infants seem to process not only the numerical division of resources but also the intentional aspects behind the allocation, differentiating between selfish and not-selfish offers.

This interpretation aligns with recent theoretical distinctions between distribution and sharing (Zhu et al., 2022). In third-party distribution paradigms, fairness judgments may primarily concern equality of outcomes because distributors are often portrayed as neutral allocators. In contrast, first-party sharing contexts inherently involve ownership, personal cost, and the regulation of self-interest. Consequently, sharing contexts may invite richer social evaluations concerning generosity, selfishness, and prosocial intentions. The present findings therefore suggest that, even during the second year of life, infants may already integrate information about equality with information about agents' social motivations.

More broadly, the current findings contribute to the growing developmental literature on the foundations of human fairness. McAuliffe et al. (2017) proposed that fairness develops from early sensitivity to unequal outcomes toward increasingly explicit and norm-based concerns regarding fairness and cooperation across childhood. Consistent with this developmental framework, previous research has shown that children as young as 3 years of age explicitly endorse equal resource allocation and increasingly engage in costly fair behavior with age, even when fairness conflicts with self-interest (Fehr et al., 2008; Smith et al., 2013). The present findings extend this developmental picture by suggesting that some of the foundations underlying later fairness norms may already be present during infancy. Specifically, infants in the current study selectively responded to selfish-unequal sharing while not treating altruistic-unequal sharing as a clear violation, raising the possibility that early fairness expectations already incorporate sensitivity to selfishness and prosocial concern for others.

At the same time, caution is warranted when interpreting the continuity between infants' implicit expectations and older children's explicit fairness reasoning. Looking-time measures provide evidence regarding infants' expectations about social events but do not directly reveal explicit moral judgments or behavioral preferences. In older children, fairness-related behavior increasingly involves executive functioning, strategic reasoning, norm enforcement, and culturally shaped fairness norms (McAuliffe et al., 2017). Future longitudinal and cross-methodological work will therefore be important for understanding how infants' early expectations regarding selfishness, fairness, and prosociality become integrated into later moral cognition and social behavior.

Several limitations should also be acknowledged. First, the present study did not verify that infants perceived red cubes as desirable resources, although we thought these cubes could work as resources based on previous studies on infants' expectations of resource distribution using neutral objects as resources (e.g., Geraci and Surian, 2011). Future studies could strengthen the results by validating the findings using desirable resources. Second, the sharing context in the present study may have been somewhat limited in ecological richness because we intentionally constrained the distributor's actions during familiarization to minimize ambiguity in resource ownership. Future studies need to utilize more explicit cues to sharing (e.g., the sharer interacts with the objects before allocation, more desirable resources are used) to elucidate infants' expectations of prosocial sharing. Third, although previous research has linked infants' own sharing behavior to their evaluations of unfair resource allocation in the third-party distribution contexts (Sommerville and Enright, 2018), the current study did not assess infants' own prosocial behavior. Thus, it remains unclear whether individual differences in sharing are directly associated with infants' expectations about fairness in first-party sharing contexts. Future research should examine this relation using both behavioral measures of infants' sharing and measures of their responses to fair and unfair sharing events. Fourth, although we included a relatively wide age range, the cross-sectional nature of this study limits our ability to investigate the developmental trajectory of fairness concerns in the sharing context. Given that both infants' sense of fairness and sharing behavior emerge in the first year of life and rapidly develop during the second year, a systematic longitudinal analysis is needed to fully understand the interplay between early prosocial behavior and fairness consideration. Such research should also examine how these expectations are shaped by infants' social environments (Franchin et al., 2019). Although recent work has begun to investigate environmental influences on early fairness development, it has focused primarily on third-party resource distribution (e.g., Meristo et al., 2025). Because sharing is embedded in everyday interactions with caregivers, siblings, and peers, these experiences may contribute to infants' developing sensitivity to selfish and prosocial sharing. Examining these developmental and environmental pathways will help clarify how infants' early expectations about sharing become integrated into the broader foundations of fairness, prosociality, and moral development.

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Footnotes

Edited by: Laura Franchin, University of Trento, Italy

Reviewed by: Antonya Gonzalez, Western Washington University, United States

Martina Vogelsang, University of Kassel, Germany