Invited speakers

Efferson, C., Lalive, R.
Irreducible cultural variation in Switzerland
A prominent hypothesis in gene-culture coevolution says that cultural evolutionary processes stabilize group-level differences that would otherwise not be possible. This kind of variation is a necessary but not sufficient condition for the cultural group to be a meaningful unit of organization - and by extension selection - in human populations. While many of us may be comfortable with the notion that cultures vary when regaling party goers with tales from our latest vacation, isolating cultural variation from other forms of group-level variation is a formidable empirical task. The challenge is that cultural boundaries often correlate with others boundaries linked, for example, to the environment or political institutions. The French-German language border in Switzerland offers an unusual opportunity to sidestep these confounds. Using a pre-registered regression discontinuity design, we analyzed several potential discontinuities related to health, reproduction, and well-being. Results show that people in the two parts of Switzerland lead different lifestyles in terms of sleep, social support, and physical activity. They do not differ, however, in terms of diverse outcomes related to fertility, physiological disease, and physiological function. The two groups do differ psychologically, with significant discontinuities associated with major depressive episodes, psychological distress, and suicide attempts. Given that the daily flow of people and ideas across the language border is extreme, Switzerland presents conditions especially unfavorable for the maintenance of cultural variation. Observed variation thus supports the claim that cultural transmission, as a distinct evolutionary process, can and does sustain grouplevel differences.

Bonner, K.
The Effects of the Social Learning Strategy Space in Gene-Culture Coevolutionary Modeling
Understanding how individuals learn socially is central to explaining aggregatelevel cultural evolution. Prior research has shown that even small heterogeneities in individual social learning strategy use can have outsized impacts on population-level cultural dynamics. Yet, most theoretical research has relied on assumptions that preclude the majority of possible strategies from ever arising in evolutionary models, potentially distorting our understanding of cultural evolution. This study aims to address this potential issue by comparing the evolutionary dynamics and stable strategies that emerge under two distinct modeling approaches. The first, Bayesian updating, imposes structured constraints on the social learning process, thereby limiting the strategy space under consideration. The second approach, using Finite State Machines, allows for an unrestricted exploration of all feasible strategies. By comparing these methods, we aim to uncover how strategy space restrictions may bias our understanding and to identify methods for safely restricting the strategy space under consideration without being subject to this bias.

Von Flüe, L., Efferson, C.
(Anti-)conformity in three dimensions: social learning in the big space between simple heuristics and general-purpose reasoning
Do people flexibly adjust to social information or rely on rigid heuristics that weight others’ behaviour by who they are and whether their goals align with their own? The answer matters because the ways individuals learn from others shape how culture changes. We ran an incentivised behavioural experiment with two roles. Demonstrators made initial choices based only on private information. Social learners then made the same choice after observing several demonstrators. Social learners encountered four informational contexts defined by two factors. One was whether the demonstrators belonged to the learner’s own group or to another group. The other was whether this group relation implied that the learner and the demonstrators shared a similar incentive structure or were likely to benefit from different options. This combination of group membership and incentive alignment dictated whether copying the majority or the minority was optimal and success therefore required flexible adjustment rather than blind conformity. To probe the role of deliberation, half of the learners completed the task under cognitive load. Cognitive load had no measurable effect, which points to a deeply rooted learning bias that is too robust for load to alter, namely a tendency to process incentive aligned information more effectively, especially when it comes from ingroup members. We repeated the design with participant pools in Switzerland and Kenya to assess cultural generality. Both samples were sensitive to group identity and incentive alignment, yet they followed markedly different overall strategies, underscoring the importance of cultural diversity in research on social learning.