Lucas Molleman

The behaviour of friends, colleagues, television hosts and social media feeds affects what we buy, how we dress, and who we vote for. People tend to be more sensitive to social influence when unsure about their beliefs and when the source is highly confident. Less is known about the relative impact of the confidence of self and others’ on social information use, and how they jointly shape social transmission. We present results of two incentivized decision-making tasks (N=203 and N=213, samples from the U.S.A.) where participants could adjust their initial estimates upon observing estimates of peers and their confidence. Adjustments were most sensitive to the confidence of others when participants’ own confidence was low. Confidence also affected heuristic strategies: confident others prompted participants to compromise and copy social information more often, rather than to stick with their initial estimates. We discuss how following confident others when uncertain can improve decision-making, but also leaves people vulnerable to sources of misinformation.

Human culture depends on people learning from one another. Cultural evolutionary theory distinguishes three transmission pathways: learning from parents (vertical), non-parental adults (oblique), and peers (horizontal), which differ in how rapidly information spreads within and across generations. During middle childhood, children's social worlds expand beyond the family, creating opportunities for all three pathways to operate simultaneously, yet their relative strength has rarely been compared directly. Using 1,262 dyads of 6-13 year-olds and their parents, we examined the relative strength of vertical, oblique, and horizontal transmission in two complementary behavioral experiments. Participants either received information from, or chose between, their own parent or child, an unrelated adult or child, and a peer while completing an estimation task. This design allowed us to separate two components of cultural transmission: whom people choose to learn from and how strongly they use information once it has been acquired. Vertical transmission emerged as the strongest pathway. This advantage was driven primarily by source selection, as children and parents overwhelmingly selected one another as information sources, with parents learning from their own child providing evidence for reverse vertical transmission. Once information had been acquired, however, information weighting differed little between vertical, oblique, and horizontal transmission. Instead, developmental differences dominated: social information use declined markedly across middle childhood and remained consistently higher in children than in parents. Together, these findings suggest that the relative strength of cultural transmission pathways is determined primarily by source selection rather than information weighting.

Human societies rely on rules to coordinate behaviour, sustain cooperation and maintain social order. Yet compliance can be fragile when rules are weakly enforced and individuals observe others violating them. Prior research shows that rule violations and other antisocial behaviours can spread through social influence, but less is known about how the severity of violations shapes these dynamics. In many real-world settings, rule-breaking occurs in degrees, from minor infractions to major violations, and individuals may not only imitate others but sometimes exceed the violations they observe. Here, we combine simulations and a behavioural experiment (n = 750) to study how the magnitude of observed rule violations shapes subsequent violations, and how this can generate escalation dynamics. Our simulations show that when individuals occasionally escalate beyond observed violations, even rare escalation can trigger a rapid shift from widespread compliance to collective rule-breaking. In our pre-registered experiment, observing major violations strongly increased rule-breaking, especially when committed by socially close others. Observing minor violations prompted many participants to follow suit and a minority to escalate beyond the violations they observed. Parameterizing the simulations with these behavioural responses shows that such escalators can disproportionately undermine collective compliance. These results highlight how asymmetric responses to rule violations and rare escalatory behaviour can transform small deviations into large-scale breakdowns of rule compliance.

Social information shapes how humans learn, decide, and coordinate. Theory predicts that social information is most valuable early in life, but how social information use changes across the lifespan remains poorly understood. Across seven belief-updating experiments with museum samples from Germany and Japan (ages 6–99 years; N = 41,015), we find a robust age-related trajectory: Social information use is highest early in life, drops sharply until late adolescence, and then rises slowly into late adulthood. Participants at all ages used social information most when it was close to their own belief, supported by convergent social inputs, and came from young adults. Female participants used slightly more social information than male participants, and participants from Germany used more social information than those from Japan. Together, these results reveal early-emerging strategic social information use and help explain information flow in age-diverse populations.

Human societies rely on rules to coordinate behaviour, sustain cooperation, and maintain social order. Yet compliance can be fragile when rules are weakly enforced and individuals observe others violating them. Prior research shows that rule violations and other antisocial behaviours can spread through social influence, but less is known about how the severity of violations shapes these dynamics. In many real-world settings, rule breaking occurs in degrees, from minor infractions to major violations, and individuals may not only imitate others but sometimes exceed the violations they observe. Here we combine simulations and a behavioural experiment (N = 750) to study how the magnitude of observed rule violations shapes subsequent violations, and how this can generate escalation dynamics. Our simulations show that when individuals occasionally escalate beyond observed violations, even rare escalation can trigger a rapid shift from widespread compliance to collective rule breaking. In our pre-registered experiment, observing major violations strongly increased rule breaking, especially when committed by socially close others. Observing minor violations prompted many participants to follow suit and a minority to escalate beyond the violations they observed. Parameterizing the simulations with these behavioural responses shows that such escalators can disproportionately undermine collective compliance. These results highlight how asymmetric responses to rule violations and rare escalatory behaviour can transform small deviations into large-scale breakdowns of rule compliance.

Social information helps improve judgments. While studies often examine how individuals use social information, few focus on the active process of searching for it, or linking the two. We examined how partisanship, an identity known to cause strong ingroup biases and polarisation, affects both social information search and use across four decision-making studies. Partisan biases emerged at distinct stages of information processing. When partisan identity was salient (election prediction), participants preferentially initiated information search from their ingroup. However, once information-seeking began, participants explored ingroup and outgroup decisions equally. Despite balanced exploration, biases re-emerged during information use: Participants relied more heavily on ingroup members’ choices and on information that aligned with their preferred political outcomes. These findings demonstrate the importance of disentangling social information search and use. They suggest that polarisation may stem less from a refusal to explore opposing views, and more from how that information is used.

Social norms are crucial to human development and social functioning. They play an important role in the formation of personal norms and intentions concerning risk‐taking and prosocial behaviors. During adolescence, the school becomes a prominent environment where individuals gain a deeper understanding of broader social norms, helping them navigate the complexities of adult society. Here, adolescents may learn social norms from two key sources: peers and teachers. While heightened sensitivity to peers is well established, less is known about the influence of teachers in shaping adolescent personal norms and intentions. We performed a pre‐registered two‐wave experiment (N = 270; M_age = 13.7 years old) to investigate how normative information from peers and teachers directly and indirectly shapes intentions for risk‐taking and prosocial behaviors. Results from our moderated mediation analysis indicate that normative information influences intentions for risk‐taking and prosociality both directly and indirectly by shaping personal norms. Furthermore, while the source does not moderate the direct effect, it does moderate the indirect pathway by influencing personal norms. In particular, adolescents tend to conform more strongly to peer norms and exhibit anti‐conformity toward teacher norms in the context of risk‐taking. Overall, our findings highlight the often overlooked importance of teachers in co‐shaping social norms during these formative years.

Introduction: Learning to navigate the many rules that regulate behavior in the adult world is a key developmental goal in adolescence. Yet, adolescents are notorious rule‐breakers. In this paper, we use behavioral experiments to examine how adolescent rule‐breaking is impacted by situational ambiguity and social influence. Methods: Younger (11−15 year‐olds, N = 296) and older adolescents (16−19 year‐olds, N = 333) recruited from high schools in the Netherlands (44% male, 54% female, 2% other) completed incentivized tasks. Each task involved a red traffic light, and participants were told that the rule was to wait until it turned green. However, by breaking the rule and crossing before the green light, they could increase their rewards. The tasks varied in two factors: situational ambiguity (a yellow light appearing before green) and peer behavior (observing peers either following or breaking the rule). Results: Adolescents' rule‐breaking is highly sensitive to ambiguity and peer influence. Rule‐breaking strongly increases when there is wiggle room to interpret a situation in self‐serving ways, and when observing rule‐breaking by peers. The magnitude of these effects does not differ between younger and older adolescents, but overall, older adolescents tend to break the rule more often than younger adolescents. Moreover, older adolescents' injunctive norms change more in response to others' behavior. Exploratory analyses indicate that boys break the rule more often and that girls are substantially more sensitive to peer influence than boys. Conclusions: Our experimental results indicate that interventions aimed at curbing adolescents' rule‐breaking may benefit from reducing situational ambiguity and promoting exposure to positive peer behavior.

Human adaptation depends on individuals strategically choosing whom to learn from. A mosaic of social learning strategies—such as copying majorities or successful others—has been identified. Influential theories conceive of these strategies as fixed heuristics, independent of experience. However, such accounts cannot explain the flexibility and individual variability prevalent in social learning. Here we advance a domain-general reward learning framework that provides a unifying mechanistic account of pivotal social learning strategies. We first formalize how individuals learn to associate social features (for example, others’ behaviour or success) with reward. Across six experiments ( n = 1,941), we show that people flexibly adjust their social learning in response to experienced rewards. Agent-based simulations further demonstrate how this learning process gives rise to key social learning strategies across a range of environments. Our findings suggest that people learn how to learn from others, enabling adaptive knowledge to spread dynamically throughout societies.