How did Charles Darwin explain sexual selection in animals?

English naturalist Charles Darwin introduced the theory of sexual selection in his 1871 work, The Descent of Man, to explain the evolution of conspicuous physical traits that appear disadvantageous to survival, such as the elaborate plumage of a peacock or the large antlers of a stag.123

Darwin proposed that these traits arise not from a struggle for existence against external conditions, but from a struggle between individuals of one sex—typically males—to secure mates. He identified two primary mechanisms for this process:13

• Mate Preference: One sex, often the female, exhibits a preference for individuals of the opposite sex that possess certain attractive traits, such as specific colors or patterns.13
• Intrasexual Competition: Individuals, usually males, develop increased strength, size, or aggressiveness to compete directly with members of the same sex for access to mates.13

By securing more mating opportunities, individuals with these traits achieve higher fitness, which offsets the risks associated with their increased visibility to predators or the physical burden of their adornments.13