Why would wasting energy make a male more attractive?
The key insight is that a wasteful display is a reliable, hard-to-fake advertisement of quality. In the East Asian cicada *Platypleura kaempferi*, males produce two types of songs: a fast, high-rate calling song to attract females from a distance, and a slower courtship song once a female approaches. Females strongly prefer males with higher calling song rates—meaning more pulses per second—because producing that fast song requires more energy and stamina [1]. Only males in good condition can sustain that high rate, so the wastefulness of the signal guarantees its honesty.
The same logic applies to humans. In a study of 388 charity runners and their 9,281 donors, runners who emphasized the subjective cost of their run (e.g., how difficult or painful it was) attracted significantly more donors [2]. Crucially, the average donation per donor did not increase—the total raised went up purely because more people donated. This shows that communicating the personal cost of an altruistic act makes the fundraiser seem more impressive and trustworthy, which is especially attractive to opposite-sex donors [2].
Doesn't this selection eventually eliminate the variation it depends on?
That's the classic 'lek paradox'—if females always choose the males with the most extravagant displays, you'd expect all males to eventually look the same, and then there's no basis for choice. But mathematical models show this isn't what happens. One model [4] demonstrates that sexual selection can actually *increase* genetic variation in display traits, not deplete it, as long as female preferences are strong enough and not too variable. In fact, under conditions like lekking (where females compare many males at once), selection can exaggerate genetic variance in male displays beyond what you'd see under random mating [4].
Another model [3] adds that females often prefer ornaments that signal a male's 'quality'—his ability to acquire and metabolize resources—rather than purely arbitrary traits. When ornaments are quality-dependent, females are willing to invest in costly mate search to find the best males. And even purely arbitrary 'Fisherian' ornaments can persist if they piggyback on preferences for quality signals [3]. So the system doesn't run out of fuel; instead, the interplay between male traits and female preferences can sustain or even amplify variation.
Is sexual selection really different from natural selection?
Yes, and the difference is crucial for understanding wasteful displays. Natural selection typically weeds out costly traits, but sexual selection actively favors them. As one review [5] argues, sexual selection is unique because it can simultaneously promote and maintain the genetic variation that fuels evolutionary change. This helps explain why traits like the peacock's train—which seem absurdly costly—can evolve: females prefer them precisely because they are costly, and that preference itself can be genetically maintained [5].
The cicada study [1] provides a concrete example: after mating, some males resumed calling, but their song rate was significantly lower than before mating, and none of them attracted a new mate. This suggests that the cost of mating depletes the male's energy reserves, making it impossible to sustain the high-quality signal needed to attract another female. So the wastefulness is not just a signal—it's a real physiological limit that enforces honesty.
About These Sources
This answer is built on 5 peer-reviewed studies — published from 2021 to 2024, 1 from 2024 or later, 3 in Q1 journals, collectively cited 52 times — selected as the most relevant from 5 studies that passed quality screening, drawn from 49 papers retrieved from a database of over 500 million.
Sources used in this answer
The best of both worlds: cicada males change costly signals to achieve mates while females choose a mate based on both calling and courtship songs
In the cicada *Platypleura kaempferi*, females prefer males with higher calling song rates (more pulses per second) and shorter pulse durations—traits that are energetically costly to produce. After mating, males that resumed calling had significantly lower song rates and failed to attract new mates, confirming the signal's cost.
Communicating the cost of your altruism makes you cool—competitive altruism and sexual selection in a real-life charity situation
In a study of 388 charity runners and 9,281 donors, runners who emphasized the subjective difficulty of their run attracted more donors and raised more total money, even though the average donation per donor did not increase. A higher communicated cost also led to a higher ratio of opposite-sex donors.
The evolution of mating preferences for genetic attractiveness and quality in the presence of sensory bias
Simulations show that female preferences evolve most readily for ornaments that signal male quality (resource acquisition), and that costly mate search is sustained by quality-dependent ornaments. Arbitrary 'Fisherian' ornaments can persist only by piggybacking on preferences for quality signals.
When does sexual selection through mate choice deplete versus exaggerate genetic variation: is there a lek paradox?
Mathematical models demonstrate that sexual selection can increase genetic variance in male display traits and female preferences under a wide range of conditions, contradicting the 'lek paradox' assumption that selection depletes variation. Variance is most exaggerated when females compare many males simultaneously (lekking).
Evolution by Sexual Selection
A review argues that sexual selection is distinct from natural selection because it can simultaneously promote and maintain genetic variation, helping to explain the evolution of costly displays like the peacock's train and even the evolution of sexual reproduction itself.