The Evolution of Beauty

Richard Prum has an interesting and controversial theory about sexual selection. Richard Prum is also really into birds.

FIRST, the theory: Charles Darwin argued that there were two types of selection. The first, natural selection, is the idea that traits that make an animal more “fit” — i.e., better at producing offspring — will be selected for and become more prevalent over time. The second, sexual selection, is the idea that traits can evolve as the result of essentially arbitrary mate choice. A female may find an ornament (a striking red feather, for example) to be particularly attractive, and may choose to mate with the male that has the largest and most striking red feather. The female may then pass this preference for red feathers to her daughters, just as the male may pass along his particularly large and striking red feather to his sons. This can result in a runaway process, with males developing ever more complex and distinctive ornaments and females developing ever more detailed and idiosyncratic preferences, even though these ornaments and preferences have no connection to “fitness.”

Followers of Darwin, however, quickly grew suspicious of his theory of sexual selection, and instead argued that sexual selection was merely a sub-category of natural selection. They developed several theories to explain sexual ornamentation within the confines of “survival of the fittest.” A striking red feather, for example, might indicate that the male is particularly resistant to disease. Or it might show that the male was particularly adept at evading predators (as one must be to survive in the jungle with a bright red target on your back). Thus, by choosing the male with the largest red feather, the female was actually improving the fitness of her offspring. These theories have dominated evolutionary biology for the last 150 years. But Prum argues that Darwin was right all along: sexual selection — i.e., the development of traits from essentially arbitrary mate choice, and without any real connection to fitness — is a distinct and powerful force in evolution.

SECOND, the birds: Richard Prum is really into birds. His passion is infectious. Even when you find yourself lost in one of his many multi-page descriptions of avian mating rituals, you can’t help but smile at the childish glee he takes in his subjects. Prum’s passion alone is reason enough to pick up The Evolution of Beauty — and if you learn something about evolutionary theory in the process, well, that’s just icing on the cake.

Good For: Birdwatchers; Darwinists.

Not Good For: Duck sex prudes (there’s a lot of duck sex).

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