In many species, males compete for access to females. Females are very selective because they want to ensure their progeny have the best genes, and they usually put a lot more resources and energy into reproduction than males do. This choosiness can lead to incredibly elaborate behaviors, coloration, and form in males that may even hinder their normal survival ability and make them stand out like sore thumbs to predators. This is because the sexual selection has outweighed the natural selection– in other words, even though the display is gaudy, the males who have it have more progeny (increased fitness), even if they don’t live as long. If male attractive traits and what that make females find those traits attractive can be genetically inherited, a phenomenon occurs called runaway selection. The attractive males get chosen by the females who are ‘programmed’ to like the traits, and the traits are amplified over time. The sexy son hypothesis, developed by Ronald Fisher in 1930, also states that females may select mates that will give their sons the traits for reproductive success, thus indirectly increasing their fitness.
However these types of traits arise, they can result in interesting, and often quite entertaining, male visual and behavioral phenotypes. Here are some of the quirkiest displays out there:
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