Indirect genetic effects clarify how traits can evolve even when fitness does not

David N Fisher* (Corresponding Author), Andrew McAdam

*Corresponding author for this work

Research output: Contribution to journalArticlepeer-review

21 Citations (Scopus)
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There are many situations in nature where we expect traits to evolve but not necessarily for mean fitness to increase. However, these scenarios are hard to reconcile simultaneously with Fisher's fundamental theorem of natural selection (FTNS) and the Price identity (PI). The consideration of indirect genetic effects (IGEs) on fitness reconciles these fundamental theorems with the observation that traits sometimes evolve without any adaptation by explicitly considering the correlated evolution of the social environment, which is a form of transmission bias. Although environmental change is often assumed to be absent when using the PI, here we show that explicitly considering IGEs as change in the social environment with implications for fitness has several benefits: (1) it makes clear how traits can evolve while mean fitness remains stationary, (2) it reconciles the FTNS with the evolution of maladaptation, (3) it explicitly includes density‐dependent fitness through negative social effects that depend on the number of interacting conspecifics, and (4) it allows mean fitness to evolve even when direct genetic variance in fitness is zero, if related individuals interact and/or if there is multilevel selection. In summary, considering fitness in the context of IGEs aligns important theorems of natural selection with many situations observed in nature and provides a useful lens through which we might better understand evolution and adaptation
Original languageEnglish
Pages (from-to)4-14
Number of pages11
JournalEvolution Letters
Issue number1
Early online date29 Jan 2019
Publication statusPublished - Feb 2019

Bibliographical note

We thank Cortland Griswold, Loeske Kruuk, Alastair Wilson, Piter Bijma, Lucas Marie-Orleach, Joel McGlothlin, and an anonymous reviewer for comments and discussions that helped to improve this manuscript. The authors declare no conflicts of interest.


  • adaptation
  • evolution
  • fundamental theorem of natural selection
  • indirect genetic effects
  • maladaptation
  • natural selection


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