This article is from the January/March 2022 journal Les Indispensables de Sciences et Avenir n°208.

Male deer have horns of disproportionate size: up to two meters in elk’s wingspan! Because the most well-equipped individuals often emerge victorious in competitions for access to women. This arms race is the result of sexual selection in its interracial version; Intersex selection, which, being the “temptation” component, promotes the development of traits involved in the choice of partners. This sometimes leads to one-off humiliations with dire consequences. Thus, the male peacock’s long train allows him to “cartwheel” to impress the females. Outside of the mating season, such a helper puts the animal at a disadvantage against the predator.

a “runaway”

But evolution has retained this asymmetry as it is an indicator of health and vigor for females… This phenomenon is very widespread among birds. In one fish, the stickleback, males have a red spot: the most conspicuous ones attract females. To explain these dissipation, experts create several possibilities. Females may select exceptional males to produce exceptional sons, who are in turn favored by females: we speak here of the “fisherian runaway”, named after the British biologist Ronald Fisher (1890–1962) is kept.

“Sexual selection is still a matter of debate”

Another explanation: Israeli ornithologist Amotz Zahvi published his “disability theory” in 1975, which stipulates that a signal must be expensive for the transmitter to be reliable for the receiver. The costly sign is for the female… an honest indication of genetic quality. “Sexual selection is still a matter of debate, Researcher Thomas Lenormand of Cefe Montpellier assures. In order to understand the importance of direct and indirect benefits, or Fisher’s runaway process, in the development of preferences, it is often difficult to separate the mechanisms at work. Sexual traits also reflect the imagination of very free co-evolution between signal and preference.”

by Pierre Vandeginste