That struck him as absurd. Worse, it’s stubbornly cold. It’s a theory of aesthetics that tries to shove aesthetics under the rug, implicitly denying that manakins and other animals could be having any kind of subjective experience. It has even crept into our understanding of ourselves: Evolutionary psychologists have put forward poorly conceived adaptive explanations for everything from female orgasms to same-sex preferences. “These ideas have saturated the popular culture. In the pages of Vogue, and in cosmetic surgery offices, you read that beauty is a revealing indicator of objective quality,” says Prum. “That’s why I had to write the book.”

The book in question, which publishes tomorrow, is The Evolution of Beauty: How Darwin's Forgotten Theory of Mate Choice Shapes the Animal World—and Us. It’s a “natural history of beauty and desire”—a smorgasbord of evolutionary biology, philosophy, and sociology, filtered through Prum’s experiences as a birdwatcher and his diverse research on everything from dinosaur colors to duck sex. Through compelling arguments and colorful examples, Prum launches a counterstrike against the adaptationist regime, in an attempt to “put the subjective experience of animals back in the center of biology” and to “bring beauty back to the sciences.”

The central idea that animates the book is a longstanding one that Prum has rebranded as the “Beauty Happens hypothesis.” It starts with animals developing random preferences—for colors, songs, displays, and more—which they use in choosing their mates. Their offspring inherit not only those sexy traits, but also the preference for them. By choosing what they like, choosers transform both the form and the objects of their desires.

Critically, all of this is arbitrary—not adaptive. Songs and ornaments and dances evolve not because they signal good genes but because animals just like them. They’re not objectively informative; they’re subjectively pleasing. Beauty, in other words, just happens. “It’s a self-organizing process, by which selection will arrive at some standard of beauty all by itself, in the absence of any adaptive benefit—or, indeed, despite maladaptive disadvantage,” says Prum.

The Beauty Happens idea isn’t an anthropomorphic one; Prum’s arguing that animals have evolved to be beautiful to themselves, not to him. It’s not a new idea either. A century ago, geneticist Ronald Fisher wrote about extreme traits and the desire for those traits co-evolving in a runaway process. “But [Fisher’s hypothesis] has been viewed as a curious idea that’s irrelevant to nature—that’s the status in most textbooks,” says Prum. He’s on a mission to re-emphasize it, and to show that aesthetics and beauty aren’t mushy subjects that science should shy away from.

It’s been an uphill struggle, partly because the arbitrary nature of the idea is so distasteful to some. Prum recalls discussing his ideas with a “well-respected, center-of-the-road, evolutionary biologist,” who took it all in and said: But that’s nihilism! “That’s when I realized that I had a marketing problem,” he says. “This is what fills me with joy to study, what literally gives me goosebumps in the office, and when I express it to my colleague, he doesn’t have a reason to get out of bed in the morning.”