Social learning is crucial for human adaptability, enabling rapid adaptation and cultural knowledge dissemination. However, reliance on social learning isn't uniform; it varies across societies, individuals, and developmental stages. Existing models highlight the importance of this variation for collective dynamics, influencing consensus-building, cooperation, and cultural evolution. Yet, the reasons behind this variation remain unclear. This research challenges the assumption of fixed social learning strategies by focusing on the evolution of developmental factors that shape reliance on social learning. The model explores the evolution of flexible developmental programs where individuals adjust their reliance on social learning based on past experiences, formalizing the idea that social learning itself is learned. The central hypothesis is that developmental flexibility in social learning will evolve if social learning benefits some but not all individuals, allowing individuals to learn from experience whether a strong reliance on social learning is beneficial. Three scenarios of increasing complexity are investigated to explore this hypothesis: 1) varying effectiveness of social learning across individuals; 2) varying payoffs from adopting cultural traits; and 3) the impact of assortment, where individuals preferentially learn from those with similar payoffs. These scenarios relax the unrealistic assumption of equal payoffs for all individuals from any cultural trait in classic cultural evolution models.

The authors review existing literature on social learning and its importance in human adaptation and cultural evolution. They highlight the inconsistencies in social learning strategies across different populations, individuals, and developmental stages. The review emphasizes the lack of a comprehensive explanation for the observed variation in social learning reliance. Several theoretical models from various fields are referenced, underscoring the significant influence of individual differences in social learning on collective dynamics. The existing literature demonstrates the impact of individual differences on the diffusion of innovations, consensus-building, and the outcomes of cultural evolution. However, a major gap remains in explaining the origins of this individual variation.

An individual-based simulation model was constructed to study the emergence of individual differences in social learning over evolutionary time. The model simulates a population of 1000 individuals over 10,000 generations, where each individual repeatedly decides whether to adopt cultural traits using either individual or social learning. Reliance on social learning (S) is not fixed but depends on experience, influenced by two evolving 'genes': initial reliance on social learning (S₀) and developmental flexibility (A). S₀ determines the initial probability of using social learning, while A dictates the degree to which past experiences influence reliance on social learning. A higher A means a stronger adjustment based on previous learning outcomes. The model incorporates a fitness cost associated with A to ensure high flexibility evolves only if it offers clear fitness benefits. Individuals sequentially decide on adopting ten cultural traits (half beneficial, half detrimental), using either individual (imperfect, noisy assessment of payoff) or social learning (imperfect assessment based on ten other individuals' outcomes). Individuals reproduce proportionally to their total payoff; offspring inherit S₀ and A with a small chance of mutation. The model assesses how S₀ and A evolve, observing individual differences in reliance on social learning at the end of development. Three scenarios were simulated: 1) varying effectiveness of social learning across individuals; 2) varying payoffs from adopting cultural traits; and 3) the impact of assortment (preferential learning from similar individuals). For each scenario, 200 independent simulations were run to obtain robust summary statistics.

The results consistently demonstrate that flexible developmental programs evolve when the value of social information is uncertain. This uncertainty leads to individual differences in reliance on social learning. In the first scenario (varying effectiveness of social learning), flexibility evolved only when there was intermediate average effectiveness and high individual variation in effectiveness. High average effectiveness led to high social learning reliance and low flexibility, while low average effectiveness resulted in low reliance and low flexibility. In the second scenario (varying payoffs from adopting traits), flexibility evolved in populations with intermediate individual variation in payoffs and high clustering of these differences (creating majority and minority groups with opposing payoff profiles). In these conditions, majority individuals increase social learning reliance, while minority individuals decrease it. High or low individual variation in payoffs led to low flexibility. Finally, in the third scenario (assortment), intermediate assortment levels produced the highest flexibility. Low assortment resulted in low reliance on social learning, while high assortment resulted in high reliance. The simulations consistently showed that flexible learning strategies evolve only under conditions of uncertainty, leading to the emergence of individual differences in social learning. Individuals in majority groups tended to rely more strongly on social learning than those in minority groups, especially when assortment was low.

The findings provide a general explanation for individual differences in social learning, showing how natural selection shapes individuals' capacity to flexibly adjust their reliance on social learning based on experience. The evolution of developmental flexibility is favored by uncertainty, whether rooted in individual differences in learning effectiveness, varying payoffs from cultural traits, or assortment levels. The model formalizes the idea that social learning strategies are themselves learned, contrasting with the traditional assumption of fixed strategies. The results may explain between-population differences in reliance on social learning, predicting high reliance in homogeneous societies (low payoff variation) and lower reliance in heterogeneous societies. The model highlights the importance of the social environment in shaping learning strategies, demonstrating that uncertainty in the social environment alone can favor the evolution of flexibility. The prediction that majority group members rely more strongly on social learning is a key implication of the study.

The study provides a novel explanation for the prevalence of individual differences in social learning by demonstrating the evolutionary advantage of flexible learning strategies under conditions of uncertainty. This flexibility, driven by unpredictable benefits of social information, leads to the emergence of individuals who either predominantly utilize social or individual learning. The model's implications extend to understanding between-population differences in social learning and the role of the social environment in shaping learning behavior. Future research could investigate more gradual variation in social learning reliance and explore the interplay between different learning mechanisms.

The model employs simplifying assumptions, such as a fixed magnitude of adjustment in reliance on social learning and equal effectiveness of learning across different cultural traits. These assumptions may oversimplify real-world complexity, potentially leading to an exaggeration of extreme individual differences in social learning reliance. Future work should explore more nuanced models, relaxing these assumptions to obtain a more precise understanding of the evolution of individual differences in social learning strategies.