This way, the effective size makes it possible to directly compare any number of complex populations-each with their own complicating factors-in a way that would otherwise be impossible. The effective population size is a theoretical construct that links complex populations to simpler, idealised models. What is effective population size and why do we need it? The funders had no role in study design, data collection and analysis, decision to publish, or preparation of the manuscript.Ĭompeting interests: The authors have declared that no competing interests exist. įunding: This research has been supported by the Max Planck Society and by the Deutsche Forschungsgemeinschaft (DFG, German Research Foundation) under Germany’s Excellence Strategy – EXC 2002/1 ”Science of Intelligence” – project number 390523135. Simulation and plotting code necessary to reproduce all results and figures in the manuscript can be found on GitHub. This is an open access article distributed under the terms of the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original author and source are credited.ĭata Availability: This manuscript does not contain any empirical data. Received: SeptemAccepted: FebruPublished: April 8, 2022Ĭopyright: © 2022 Deffner et al. Meiji University School of Interdisciplinary Mathematical Science, JAPAN Our results highlight the importance of effective sizes for cultural evolution and provide heuristics for empirical researchers to decide when census numbers could be used as proxies for the theoretically relevant effective numbers and when they should not.Ĭitation: Deffner D, Kandler A, Fogarty L (2022) Effective population size for culturally evolving traits. Specifically, we provide a formal derivation for cultural effective population size and use mathematical and computational models to study how effective size and cultural diversity depend on (1) the way culture is transmitted, (2) levels of migration and cultural exchange, as well as (3) social network structure. the size that matters for important evolutionary outcomes) to understand how and when larger populations can be expected to be more culturally diverse. We employ insights from population genetics about the “effective” size of a population (i.e. Our approach is based on cultural evolutionary theory which applies ideas about evolution to understand how cultural traits change over time. Human populations show immense cultural diversity and researchers have regarded population size as an important driver of cultural variation and complexity. Extending previous work, our results highlight the importance of carefully defining effective population size for cultural systems and show that inferring N e requires detailed knowledge about underlying cultural and demographic processes. For connectedness, however, even small amounts of migration and cultural exchange result in high diversity independently of N e. For one-to-many transmission and different network structures, larger effective sizes are closely associated with higher cultural diversity. Network density in random networks leaves N e unchanged, scale-free networks tend to decrease and small-world networks tend to increase N e compared to census numbers. We caution that migration and cultural exchange can have counter-intuitive effects on N e. We show that one-to-many and frequency-dependent transmission can temporally or permanently lower effective population size compared to census numbers. We use mathematical and computational modeling approaches to investigate how cultural N e and levels of diversity depend on (1) the way traits are learned, (2) population connectedness, and (3) social network structure. Here, we examine the concept of effective population size for traits that evolve culturally, through processes of innovation and social learning. Results from population genetics, however, demonstrate that in populations with complex demographic structure or mode of inheritance, it is not the census population size, N, but the effective size of a population, N e, that determines important evolutionary parameters. Population size has long been considered an important driver of cultural diversity and complexity.
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