Fisherian Runaway Selection

Origins and basic logic

Charles Darwin (1871) proposed the theory of sexual selection, under which traits that seem harmful to survival, such as the peacock's tail, can evolve through mate choice, but he did not fully explain why females came to prefer such traits. Ronald Fisher (1915, 1930) pointed out that if females that prefer a trait that initially carries a slight advantage mate with males bearing that trait, their offspring will inherit both the trait and the preference. This creates a genetic correlation between preference and trait, setting up a positive feedback in which the preference strengthens as the trait grows, so the trait can become exaggerated in a runaway fashion. The process can continue until it is balanced by the survival costs imposed by natural selection.

Mathematical models and the sexy son hypothesis

Fisher's idea was long expressed only verbally until O'Donald (1962) carried out early mathematical analyses, and Lande (1981) and Kirkpatrick (1982) formalized it rigorously using quantitative and population genetic models. Lande showed that runaway occurs when the genetic covariance between trait and preference is large enough, and that populations can evolve in different directions, promoting speciation. In this view the benefit to females is sexy sons, who inherit the attractive trait and enjoy mating success. Pomiankowski, Iwasa and Nee (1991) analyzed conditions under which biased mutation sustains runaway when preferences are costly. Prum (2010) argued that the Lande–Kirkpatrick mechanism should be treated as the null model in research on sexual selection.

Comparison with the handicap principle and experimental evidence

A contrasting theory is Zahavi's (1975) handicap principle. The handicap principle sees costly ornaments as honest signals of a male's real quality, while the runaway model holds that a trait can be selected for its attractiveness alone, independent of quality. Kokko et al. (2003) argued that the two mechanisms lie on a single continuum. As experimental evidence, Andersson (1982) showed that artificially lengthening the tails of African long-tailed widowbirds increased their mating success, and Wilkinson and Reillo (1994) observed a correlated response in stalk-eyed flies, in which artificial selection on male eyestalk length also changed female preferences. Andersson's Sexual Selection (1994) synthesized a wide range of such research.

FAQ

What is Fisherian runaway selection in simple terms?

It explains how an ornament that females like and the tendency to like it are passed on together to offspring and drive each other on, so the ornament becomes ever more exaggerated.

How does it differ from the handicap principle?

The handicap principle holds that costly ornaments reveal good male quality, while runaway selection holds that ornaments can spread simply because they are attractive, regardless of quality.

Sources reviewed: 2026-10-26

References

1. Darwin, C. (1871). The Descent of Man, and Selection in Relation to Sex. London: John Murray.
2. Fisher, R. A. (1915). The evolution of sexual preference. Eugenics Review, 7(3), 184–192.
3. Fisher, R. A. (1930). The Genetical Theory of Natural Selection. Oxford: Clarendon Press.
4. O'Donald, P. (1962). The theory of sexual selection. Heredity, 17(4), 541–552.
5. Lande, R. (1981). Models of speciation by sexual selection on polygenic traits. Proceedings of the National Academy of Sciences, 78(6), 3721–3725.
6. Kirkpatrick, M. (1982). Sexual selection and the evolution of female choice. Evolution, 36(1), 1–12.
7. Zahavi, A. (1975). Mate selection: A selection for a handicap. Journal of Theoretical Biology, 53(1), 205–214.
8. Andersson, M. (1982). Female choice selects for extreme tail length in a widowbird. Nature, 299(5886), 818–820.
9. Pomiankowski, A., Iwasa, Y., & Nee, S. (1991). The evolution of costly mate preferences I. Fisher and biased mutation. Evolution, 45(6), 1422–1430.
10. Andersson, M. (1994). Sexual Selection. Princeton: Princeton University Press.
11. Wilkinson, G. S., & Reillo, P. R. (1994). Female choice response to artificial selection on an exaggerated male trait in a stalk-eyed fly. Proceedings of the Royal Society B, 255(1342), 1–6.
12. Kokko, H., Brooks, R., Jennions, M. D., & Morley, J. (2003). The evolution of mate choice and mating biases. Proceedings of the Royal Society B, 270(1515), 653–664.
13. Prum, R. O. (2010). The Lande–Kirkpatrick mechanism is the null model of evolution by intersexual selection. Evolution, 64(11), 3085–3100.