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Evolutionary dynamics of culturally transmitted, fertility-reducing traits.

Authors
  • Wodarz, Dominik1, 2
  • Stipp, Shaun2
  • Hirshleifer, David3
  • Komarova, Natalia L2
  • 1 Department of Population Health and Disease Prevention, Program in Public Health, Susan and Henry Samueli College of Health Sciences, University of California, Irvine, CA 92697, USA.
  • 2 Department of Mathematics, University of California, Irvine, CA 92697, USA.
  • 3 Paul Merage School of Business, University of California, Irvine, CA 92617, USA.
Type
Published Article
Journal
Proceedings of The Royal Society B Biological Sciences
Publisher
The Royal Society
Publication Date
Apr 29, 2020
Volume
287
Issue
1925
Pages
20192468–20192468
Identifiers
DOI: 10.1098/rspb.2019.2468
PMID: 32290801
Source
Medline
Keywords
Language
English
License
Unknown

Abstract

Human populations in many countries have undergone a phase of demographic transition, characterized by a major reduction in fertility at a time of increased resource availability. A key stylized fact is that the reduction in fertility is preceded by a reduction in mortality and a consequent increase in population density. Various theories have been proposed to account for the demographic transition process, including maladaptation, increased parental investment in fewer offspring, and cultural evolution. None of these approaches, including formal cultural evolutionary models of the demographic transitions, have addressed a possible direct causal relationship between a reduction in mortality and the subsequent decline in fertility. We provide mathematical models in which low mortality favours the cultural selection of low-fertility traits. This occurs because reduced mortality slows turnover in the model, which allows the cultural transmission advantage of low-fertility traits to outrace their reproductive disadvantage. For mortality to be a crucial determinant of outcome, a cultural transmission bias is required where slow reproducers exert higher social influence. Computer simulations of our models that allow for exogenous variation in the death rate can reproduce the central features of the demographic transition process, including substantial reductions in fertility within only one to three generations. A model assuming continuous evolution of reproduction rates through imitation errors predicts fertility to fall below replacement levels if death rates are sufficiently low. This can potentially explain the very low preferred family sizes in Western Europe.

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