Richard Prum spends most of his time studying birds. But this year, the award-winning evolutionary ornithologist has also produced an unexpected feminist manifesto.

In his new book, The Evolution of Beauty: How Darwin’s Forgotten Theory of Mate Choice Shapes the Animal World—And Us, Prum, an evolutionary ornithologist at Yale, challenges the dominant narrative among evolutionary biologists: that beauty and sexual ornaments, such as a peacock’s plumage, a deer’s antlers, or the size of a man’s penis, evolve for adaptive reasons. Traditional theory holds that these ornaments are designed to display good genes, attract females, and help the species reproduce. It also tends to characterize the female orgasm as either a tool for genetic subterfuge, or an evolutionary mistake.

Per the adaptive theory, the male orgasm motivates men to seek out more opportunities for ejaculation, and subsequently, reproduction. The female orgasm, meanwhile, has remained something of a mystery. Some evolutionary biologists theorized that it evolved to literally “upsuck” the sperm of genetically superior men. (This would have let women raise their children with kind, reliable, not-so-hot partners, while passing on the superior genes of the men they mated with on the side.) The other dominant theory, championed by anthropologist Donald Symons in his 1979 book The Evolution of Human Sexuality, holds that the female orgasm, like male nipples, evolved as a byproduct of natural selection.

Prum posits a different—and coincidentally, far more appealing—explanation: that female sexual pleasure is in fact the central force behind the mating process. Basically, the female orgasm exists because it feels good, and women naturally sought out partners who could provide them with pleasurable feelings.

“The aesthetic proposal is that human female sexual pleasure and orgasm have evolved because females have preferred to mate, and remate, with males who stimulated their own sexual pleasure,” writes Prum, and that “females have thereby also selected indirectly for those genetic variations that contributed to the expansion of their own pleasure.” In other words, women had the ability to evaluate the experience of sex, and chose (naturally enough) to have sex with men who gave them orgasms. This led male mating behavior to coevolve with female desire. As male behavior evolved to meet women’s preferences, so did women’s capacity for sexual pleasure, becoming more complex, intense, and satisfying.

In this scenario, “female orgasm is not an adaptation to accomplish any extrinsic, naturally selected function,” writes Prum. “Rather, female sexual pleasure and orgasm are the evolutionary consequences of female desire and choice, and they are ends unto themselves.”

Prum puts forth several points to back up his theory about how pleasure influences evolution. For one thing, women’s orgasms are highly variable. If they are the result of indirect sexual selection, rather than direct natural selection, it makes sense that female orgasms would be more inconsistent.

This theory could also explain why human copulation, which lasts several minutes on average, is significantly longer than gorillas’ and chimpanzees’ seconds-long sex. Copulating for a longer period of time doesn’t increase the likelihood that the female will get pregnant—but humans may have evolved to have longer sexual encounters to enhance pleasure. The diversity of humans’ sex positions, compared to gorilla and chimpanzees’ consistent mounting from behind, also suggests that we’ve evolved toward the goal of servicing female clitoral stimulation and pleasure, says Prum.

Last, the pleasure theory completely aligns with the fact that female orgasm is unnecessary for procreation: “The female orgasm might have evolved to be so expansive and prodigious because it has no evolved function,” writes Prum. “It is sexual pleasure for its own sake, which has evolved purely as a consequence of women’s pursuit of pleasure.” The same cannot be said of male orgasm, which is limited in magnitude, frequency, and duration because of the link between orgasm and ejaculation.

Perhaps the most astounding element of Prum’s feminist evolutionary theories is that he’s not the first to think of them. In an under-cited passage of The Descent of Man, Charles Darwin, the revered father of evolutionary biology, proposed that sexual displays in animals evolve precisely because animals select for pretty things—or, in his words “through appreciation of the beautiful … and through the exertion of a choice.” This passage—ignored by centuries of biologists who fervently sidelined the influence of subjective pleasure—is the driving force behind Prum’s narrative.

For too long, evolutionary biologists have ignored the subjective experience of pleasure. With any luck, Prum’s book will expose the ways in which patriarchal thinking shapes scientific research—and help the public to understand that evolution is the result of women’s choice.