In The Evolution of Beauty (Doubleday, 2017), Richard O. Prum, a professor of ornithology at Yale, revives a long-neglected Darwinian idea: the claim that ornamental traits in animals — the curl of antlers, the gold splash of plumage, the trill of birdsong — are produced by aesthetic preferences. Darwin was troubled by the ubiquity of "useless beauty" in the animal world. Everywhere he looked he saw traits that were attractive but maladaptive. "The sight of a feather in a peacock’s tail," he famously wrote, "whenever I gaze at it, makes me sick!" Prum insists, following Darwin, that such display traits evolve because they are attractive — not because they signal an animal’s fitness.
Prum’s defense of nonadaptive mate choice is the latest shot fired in a long war within evolutionary biology about how far natural selection, rather than other mechanisms such as sexual selection, can explain the evolution of physical traits. In a seminal 1979 essay, "The Spandrels of San Marco," Stephen Jay Gould and Richard C. Lewontin cautioned scientists against presuming that all biological traits are adaptations. Many traits are byproducts of adaptations, or genetically linked to adaptive traits — not selected for in their own right.
Nearly four decades later, adaptationism still rules evolutionary biology. Evolutionary scientists, when examining a given organ or structure, typically begin, the philosopher of science Elisabeth Lloyd observes, by asking "What is the function of this trait?" instead of the more modest "Does this trait have a function?" Traits are assumed adaptive until proven otherwise.
The world brims with adaptations: the dangling tongue of an anteater, the bulging hump of a camel. But other evolutionary factors also affect biological traits. A maladaptive characteristic can persist because of embryological constraints, or because prior adaptations have blocked off more optimal evolutionary pathways. Other biological features evolve as byproducts of traits strongly selected for in the opposite sex of the species. Male nipples, for example, are a "useless" byproduct trait, present because of strong selection on nipples in females. Prum, like Gould and Lewontin — and, for that matter, like Darwin — sees evolutionary change as having multiple causes.
Yet because adaptive explanation remains the field’s gold standard, many evolutionary biologists have recast sexual selection as natural selection by other means. The most influential version of this recasting is the "handicap principle" developed by the Israeli evolutionary biologist Amotz Zahavi. According to Zahavi, sexual ornaments (such as the male peacock’s tail) signal adaptive fitness by imposing a survival cost — a handicap — on the signaler. Males who survive despite their costly ornaments are likely to have "better" genes. A mating preference for a costly display trait, to this view, is adaptive: The sexual ornament provides honest information about mate quality.
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Beauty differs from the other ideals with which it is often grouped — truth, goodness, justice — in that its presence in the world is not disputable. To deny the existence of beauty is to reject the evidence of our senses. When we are in the presence of beauty, Plato writes, "the whole soul seethes and throbs" in a stinging composite of anguish and joy.
Beauty, in other words, is a sensuous, bodily experience. By locating aesthetic perception in nonhuman animals, by marking the close relation between aesthetic preferences and sexuality, and by theorizing about the neural mechanisms that govern judgments of beauty, Prum and Ryan restore beauty to the body. This expansion of "beauty studies" to biology signals a shift from the ascetic to the aesthetic — from beauty as purified ideal to beauty as a fact of ordinary perception. Yet this somatization of beauty is no disenchantment. The ubiquity of sexual selection suggests that aesthetics helped determine the development of the organic world.
In the monastic culture of academic study in an age of austerity, the lure of beauty will almost always lose to the (equally seductive) promise of the clarity fueled by self-denial. And yet the academy remains, in other ways, the holding ground for aesthetic sensibility in a period that places scant value on natural or artistic beauty. Scholars in the humanities are fond of saying that the aesthetic yearnings of human beings express, and nourish, our humanity. If aesthetic desires have shaped the course of evolution, as Prum and Ryan would have us think, then a stronger claim seems possible. It may be no exaggeration to say that the longing for beauty, felt over countless generations, has literally made us human — and made, beyond us, a world of endless forms.
- A shift from the ascetic to the aesthetic is underway. At its center: evolutionary biology.
Prum’s defense of nonadaptive mate choice is the latest shot fired in a long war within evolutionary biology about how far natural selection, rather than other mechanisms such as sexual selection, can explain the evolution of physical traits. In a seminal 1979 essay, "The Spandrels of San Marco," Stephen Jay Gould and Richard C. Lewontin cautioned scientists against presuming that all biological traits are adaptations. Many traits are byproducts of adaptations, or genetically linked to adaptive traits — not selected for in their own right.
Nearly four decades later, adaptationism still rules evolutionary biology. Evolutionary scientists, when examining a given organ or structure, typically begin, the philosopher of science Elisabeth Lloyd observes, by asking "What is the function of this trait?" instead of the more modest "Does this trait have a function?" Traits are assumed adaptive until proven otherwise.
The world brims with adaptations: the dangling tongue of an anteater, the bulging hump of a camel. But other evolutionary factors also affect biological traits. A maladaptive characteristic can persist because of embryological constraints, or because prior adaptations have blocked off more optimal evolutionary pathways. Other biological features evolve as byproducts of traits strongly selected for in the opposite sex of the species. Male nipples, for example, are a "useless" byproduct trait, present because of strong selection on nipples in females. Prum, like Gould and Lewontin — and, for that matter, like Darwin — sees evolutionary change as having multiple causes.
Yet because adaptive explanation remains the field’s gold standard, many evolutionary biologists have recast sexual selection as natural selection by other means. The most influential version of this recasting is the "handicap principle" developed by the Israeli evolutionary biologist Amotz Zahavi. According to Zahavi, sexual ornaments (such as the male peacock’s tail) signal adaptive fitness by imposing a survival cost — a handicap — on the signaler. Males who survive despite their costly ornaments are likely to have "better" genes. A mating preference for a costly display trait, to this view, is adaptive: The sexual ornament provides honest information about mate quality.
[---]
Beauty differs from the other ideals with which it is often grouped — truth, goodness, justice — in that its presence in the world is not disputable. To deny the existence of beauty is to reject the evidence of our senses. When we are in the presence of beauty, Plato writes, "the whole soul seethes and throbs" in a stinging composite of anguish and joy.
Beauty, in other words, is a sensuous, bodily experience. By locating aesthetic perception in nonhuman animals, by marking the close relation between aesthetic preferences and sexuality, and by theorizing about the neural mechanisms that govern judgments of beauty, Prum and Ryan restore beauty to the body. This expansion of "beauty studies" to biology signals a shift from the ascetic to the aesthetic — from beauty as purified ideal to beauty as a fact of ordinary perception. Yet this somatization of beauty is no disenchantment. The ubiquity of sexual selection suggests that aesthetics helped determine the development of the organic world.
In the monastic culture of academic study in an age of austerity, the lure of beauty will almost always lose to the (equally seductive) promise of the clarity fueled by self-denial. And yet the academy remains, in other ways, the holding ground for aesthetic sensibility in a period that places scant value on natural or artistic beauty. Scholars in the humanities are fond of saying that the aesthetic yearnings of human beings express, and nourish, our humanity. If aesthetic desires have shaped the course of evolution, as Prum and Ryan would have us think, then a stronger claim seems possible. It may be no exaggeration to say that the longing for beauty, felt over countless generations, has literally made us human — and made, beyond us, a world of endless forms.
- A shift from the ascetic to the aesthetic is underway. At its center: evolutionary biology.
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