A dynamical model for the origin of anisogamy

Joseph D. Johnson*, Nathan L. White, Alain Kangabire, Daniel M. Abrams

*Corresponding author for this work

Research output: Contribution to journalArticlepeer-review


The vast majority of multi-cellular organisms are anisogamous, meaning that male and female sex cells differ in size. It remains an open question how this asymmetric state evolved, presumably from the symmetric isogamous state where all gametes are roughly the same size (drawn from the same distribution). Here, we use tools from the study of nonlinear dynamical systems to develop a simple mathematical model for this phenomenon. Unlike some prior work, we do not assume the existence of mating types. We also model frequency dependent selection via “mean-field coupling,” whereby the likelihood that a gamete survives is an increasing function of its size relative to the population's mean gamete size. Using theoretical analysis and numerical simulation, we demonstrate that this mean-referenced competition will almost inevitably result in a stable anisogamous equilibrium, and thus isogamy may naturally lead to anisogamy.

Original languageEnglish (US)
Article number110669
JournalJournal of Theoretical Biology
StatePublished - Jul 21 2021


  • Anisogamy
  • Evolution
  • Evolutionary game theory
  • Isogamy
  • Natural selection

ASJC Scopus subject areas

  • General Agricultural and Biological Sciences
  • Applied Mathematics
  • General Biochemistry, Genetics and Molecular Biology
  • General Immunology and Microbiology
  • Statistics and Probability
  • Modeling and Simulation


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