Applying invasion criterion to cultural evolution

Abstract

Cultural diversity is a fundamental aspect of human life and a driver of innovation; however, the underlying mechanisms remain poorly understood. While previous studies focused on how innovation generates cultural diversity, we investigated whether ecological theory, specifically the invasion criterion for understanding species coexistence in community ecology, could predict the maintenance of cultural diversity under various social learning biases. Using mathematical and individual-based models, we showed that the invasion criterion reliably predicts the duration of coexistence in the stochastic dynamics of multiple cultural traits under content-, conformity-, and anticonformity-biased social learning as well as under unbiased learning. The invasion criterion predicted moderate cultural coexistence under two types of model-biased social learning: prestige and success biases. In contrast, similarity-biased social learning, where people tend to learn from those with the same "tag" traits (e.g., gender, language), breaks the predictive power of the invasion criterion because the cultural traits were associated with the tag traits. Our results demonstrate that ecological theory offers valuable tools for understanding cultural evolution, but modifications are required to account for dynamic learning environments. Our model also showed that increasing the number of cultural models can prolong cultural coexistence under certain biases, with implications for fostering innovation and preserving culture. These findings bridge the ecological and cultural evolutionary theories and offer a unified framework for studying diversity maintenance across biological and cultural domains. Significance statementCultural diversity benefits societal innovation and environmental adaptation, but how it is maintained remains unclear. This study applies the invasion criterion, an ecological concept, to predict how long different cultural traits coexist in a population. Simulations and mathematical analyses indicated that this ecological concept is appropriate for many types of social learning but fails for learning from similar individuals. Our mathematical analysis also showed that increasing the number of role models can support or hinder cultural diversity depending on the learning strategy. This work bridges biology and culture and offers new insights into how diversity persists.