Fisherian runaway selection

Definition

An evolutionary process in which a female mating preference and the male trait it favors become genetically correlated, leading to mutually reinforcing selection that drives the trait to exaggerated, often maladaptive extremes. Named for Ronald A. Fisher, who proposed that preference and trait coevolve because offspring of choosy females inherit both the preferred trait (in sons) and the preference itself (in daughters), creating positive feedback independent of trait utility.

Etymology

From Ronald A. Fisher, British evolutionary biologist who formalized the theory in 1930; "runaway" describes the self-reinforcing, accelerating nature of the process.

Example

In stalk-eyed flies (Diopsidae), males with longer eye-stalks attract more mates despite the metabolic cost and flight maneuverability penalties of extreme ornamentation; females preferring longer stalks produce sons with longer stalks and daughters with stronger preferences, accelerating divergence between populations.

Synonyms

• Fisherian runaway
• runaway sexual selection
• Fisher's runaway process

Related Terms

• Sexual selection
• handicap principle
• sensory bias
• good genes hypothesis
• secondary sexual trait
• Lek
• epigamic selection

Usage Notes

Distinguished from "good genes" models where traits signal underlying fitness, and from sensory/cognitive bias models where preferences predate trait evolution. Runaway selection is frequency-dependent: trait advantage declines as it becomes common, but preference advantage persists. Often contrasted with the handicap principle, though both can operate simultaneously. The process predicts trait-preference genetic correlation, which has been tested in Drosophila and field crickets.