[POS] Evolution and Genetics

[POS-50] One-Way Switching of Cultural Traits Serves a Function Intrinsically Similar to Social Conformism

*Rinto Yoshizaki¹, Motohide Seki¹ (1. Kyushu Univ. (Japan))

Keywords:

Cultural Evolution,Trait Transmission,Conformist Bias,Timing of Trait Switching

Theoretical studies of cultural evolution apply modeling frameworks from population genetics, treating cultural traits—such as technologies, religions, and languages—like alleles. This approach helps simplify complex social science problems and provides new insights into human populations. A key question in cultural evolution is whether and how a newly appeared cultural trait spreads in a population. Previous models have shown that factors such as trait attractiveness, learning biases, and transmission pathways affect this process. For instance, social learning with conformity biases—preferences for majority or minority traits—can lead to complex outcomes—the emergence of unstable or stable interior equilibrium. Most of the models involving traits A and B assume bi-directional switching, that is, some of the A-individuals switch to B, and at the same time step, some B-individuals switch to A. However, in real societies, a switching often occurs tied to specific events such as rituals. Therefore, it is important to consider the case that switching from B to A and that from A to B do not take place simultaneously. In addition, some anthropological studies reported that the switching direction alternates periodically with each step. Nevertheless, the repetition of uni-directional switching has rarely been modeled. In this study, we compared bi-directional and uni-directional switching by developing models sharing the same basic structure to examine how the timing of switching events influences the outcomes. In the bi-directional case, when individuals make choices based solely on the attractiveness of traits, there are only trivial equilibrium states, and the more attractive trait is always fixed in the population. Non-trivial dynamics require conformity biases; With positive conformity, the model can exhibit bistability, in which case outcomes depend on initial conditions. With negative conformity, both traits can persist. In contrast, the uni-directional model allows bistability even in the absence of conformity. Furthermore, the diffusion dynamics are strongly influenced by two key parameters: the attractiveness of the traits, and the proportion of individuals eligible to switch at each time step. The values of these parameters determine the evolutionary outcome—whether one trait becomes fixed or bistability emerges.