A FINALIST FOR THE PULITZER PRIZENAMED A BEST BOOK OF THE YEAR BY THE NEW YORK TIMES BOOK REVIEW, SMITHSONIAN, AND WALL STREET JOURNALA major reimagining of how evolutionary forces work, revealing how mating preferences—what Darwin termed “the taste for the beautiful”—create the extraordinary range of ornament in the animal world. In the great halls of science, dogma holds that Darwin’s theory of …
In the great halls of science, dogma holds that Darwin’s theory of natural selection explains every branch on the tree of life: which species thrive, which wither away to extinction, and what features each evolves. But can adaptation by natural selection really account for everything we see in nature?
Yale University ornithologist Richard Prum—reviving Darwin’s own views—thinks not. Deep in tropical jungles around the world are birds with a dizzying array of appearances and mating displays: Club-winged Manakins who sing with their wings, Great Argus Pheasants who dazzle prospective mates with a four-foot-wide cone of feathers covered in golden 3D spheres, Red-capped Manakins who moonwalk. In thirty years of fieldwork, Prum has seen numerous display traits that seem disconnected from, if not outright contrary to, selection for individual survival. To explain this, he dusts off Darwin’s long-neglected theory of sexual selection in which the act of choosing a mate for purely aesthetic reasons—for the mere pleasure of it—is an independent engine of evolutionary change.
Mate choice can drive ornamental traits from the constraints of adaptive evolution, allowing them to grow ever more elaborate. It also sets the stakes for sexual conflict, in which the sexual autonomy of the female evolves in response to male sexual control. Most crucially, this framework provides important insights into the evolution of human sexuality, particularly the ways in which female preferences have changed male bodies, and even maleness itself, through evolutionary time.
The Evolution of Beauty presents a unique scientific vision for how nature’s splendor contributes to a more complete understanding of evolution and of ourselves.
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I picked this book up innocently, but I was only a few pages into it when I realized that it was pursuing a line of thinking that I have been toying with for the past several years. As I see it, women in industrialized societies are selecting for different characteristics in the men they choose as husbands than they have in the past.
Two things are happening: First, women no longer need to select men who can physically protect or economically support them and their children. Modern societies are safe, and women have increasingly equal access to the economic world. And, second, as women move into the world that has, until recently, been a male realm, they are demanding that men treat them differently. Modern women want to be treated as co-equals and, importantly, to have full autonomy over their sexuality; that is that they not be subjected to unwanted or forced sexual demands.
Women evolving men
The demand for sexual autonomy is most notable in the #MeToo movement. Women are making a strong demand that men keep their hands and leers off them. In response, the culture is changing and, as it changes, women are looking for different characteristics in their mates. Women are evolving men.
(Ironically, the women who select for modern co-equal characteristics in their male partners tend to have low fertility rates—often less than two children. Consequently, these women risk self-selecting themselves and their newly evolved men right out of the gene pool.)
Plum’s thesis
Standard evolutionary theory claims that when random genetic mutations confer an adaptive advantage to an organism, that organism is more likely to survive and thus pass its genes onto succeeding generations. In other words, adaptive change drives morphological change.
Plum, however, resurrects an argument that Darwin made in The Descent of Man that most evolutionary biologists have, since Darwin, dismissed. Plum argues that sexual selection also drives morphological change and that—this is the kicker—the selection is a-adaptive. That is that the selected characteristic does not (necessarily) aid the organism’s survival and can, in fact, can diminish it.
Sexual selection in birds
Plum is an ornithologist, and most of his examples are of birds. Any beginning birder quickly discovers that in most bird species, either the two sexes look identical (ravens, seagulls, penguins) or that the male is more colorful and ornamented than the female. In the first instance, this is because both sexes select each other and in the second because the female selects the male.
Continuing Darwin’s argument, Plum argues that the female selects, not only for adaptability but also for beauty. Hence the title of the book. (It is not clear to me that the female selects for beauty or that what the females are selecting for, humans find beautiful.)
What sexual selection (at least among birds) has produced is mind-boggling in terms of complexity, intricacy, and beauty. As an aside, it is one of the great joys of living in the 21st century that everything you want to see has been filmed and posted to YouTube. Every male courtship display that Plum describes is up there. You must read this book next to a computer.
In addition to selecting for beauty, Plum argues that the females of some species also select for sexual autonomy. Male ducks, apparently are the Harvey Weinsteins of the bird world. The males force copulation (biologists do not use the word rape—too much baggage) on females. To facilitate this, they have evolved long (some longer than their body length) corkscrew penises to force entry. (You can see duck rape on YouTube as well). Females have evolved vaginas that corkscrew in the opposite direction to prevent entry (They relax their vaginal walls, de-corkscrewing, to let their chosen mate in).
A less dramatic example is the bower that a male bowerbird makes. Female bowerbirds, Plum argues, select for males that build bowers that provide both an aesthetic and a safe space by erecting a physical barrier that protects them from the male while he’s doing his courtship display.
Sexual selection among humans
You can see where this is all going and, in fact, Plum’s last chapter details what sexual selection has produced—physiologically and behaviorally—in humans.
We, men, should be endlessly appreciative for women selecting for our large penises (relative to other primates, but not, apparently, to mallards). Also, claims Plum, women self-selected for their extraordinary capacity to orgasm. The females of only a tiny number of nonhuman species (3?) orgasm. (Because such behaviors must be investigated with the aid of laboratory sex toys and the exertions of diligent scientists, female orgasm in some species—elephant and blue whale, for example—has not yet been definitively determined).
But to close the circle. Plum argues that human females also select for their sexual autonomy and have over millions of years reduced the male on male aggression (and increased male social tolerance) that exists among most of our primate cousins (the startling exception is the bonobo). It is male aggression that, in turn, drives coercive sexual behaviors within primate species. Unanswered is the question of how early female hominids evolved mate choice. Female chimps and gorillas have essentially none.
Thus the #MeToo movement is yet one more step in the female-driven evolution of the human species.
It will be interesting to see—eons hence—where we end up.
Caveat
I cringe every time an evolutionary biologist or psychologist says “because.” “The female manikin selects males with yellow legs because she finds them beautiful.” Really!? How do they know? They don’t. They are just making that up. Keep that in mind.
Parts interesting, parts boring.