In 1757, David Hume argued in his book Standard of Taste that beauty is in the eye of the beholder. “Beauty,” he said, “is no quality in things themselves: It exists merely in the mind which contemplates them; and each mind perceives a different beauty.”

This naturally raises a question: Why is this standard of beauty in the eye of that beholder? A century after Hume, Darwin laid the foundation—evolution by natural selection—for a psychology that explains why: beauty is a perception of fitness payoffs on offer, such as the payoff for eating that apple or dating that person. This perception will differ—from species to species, person to person, and even time to time—as needs and niches differ. Reproductive success depends on collecting fitness points. Beauty tells us what and where they are.

Evolutionary psychology makes new, and surprising, predictions about our judgments of human beauty. Each time, for instance, that you glance at a face, you scrutinize its eyes—scoring them on a checklist of details— and arrive, through unconscious deliberation, at a verdict on their beauty. What women find attractive about the eyes of a man sometimes differs from what men find attractive about the eyes of a woman. Our ancestors relied on this unwritten checklist for millennia, but the new science of beauty has revealed some of its items. We discuss these items and the logic of their discovery, as well as some practical applications.

The predictions of evolution about beauty are surprising but, as we will see in chapter nine, its predictions about physical objects are disconcerting: objects, like beauty, are in the eye of the beholder and inform us about fitness—not about objective reality. To prepare us for the perplexing case of objects, let’s warm up our intuitions by exploring the perception of beauty in the animal kingdom.Male jewel beetles, Julodimorpha bakewelli, have a thing for beautiful females. The males fly about, searching for females, which are shiny, dimpled, and brown. Recently, some male primates of the Homo sapiens species have been driving through the beetle’s haunts in Western Australia and littering the outback with emptied beer bottles, known as “stubbies.” As it happened, some of the stubbies were shiny, dimpled, and just the right shade of brown to catch the fancy of male beetles. Forsaking real females, the male beetles swooned over stubbies with their genitalia everted, and doggedly tried to mate despite glassy rebuffs. (A classic case of the male leaving the female for the bottle.) Adding injury to insult, ants of the species Iridomyrmex discors learned to loiter near stubbies, wait for the befuddled and priapistic beetles, and then devour them, genitalia first, as they failed to have their way.

The poor beetles teetered on extinction, and Australia had to change its beer bottles to save its beetles.

This blunder of the beetle is surprising. Male beetles have mated with females for untold thousands of years. You would think that they surely know their females. Apparently not. Even when a male crawls all over his stubby—enjoying full embodied contact—he perceives it as a Siren, a 370-milliliter Amazon of irresistible allure.

Something is awry. Why should a beetle fall for a bottle? Is it due, perhaps, to his tiny brain? Perhaps mammals, with their bigger brains, would never make such a silly mistake. But they do. Moose in Alaska, Montana, and elsewhere have been found, and photographed, mating with metal statues of moose, and even bison, sometimes for hours on end. We can laugh, but Homo sapiens has its own checkered history, including sex dolls that starred centuries ago in Mughal paintings of India, and robots that star today in the International Congress on Love and Sex With Robots. Our bigger brains guarantee no inerrant attraction to bona fide human beauties.

What, then, is beauty? Surprisingly, given the panoply of foibles besetting beetles, moose, Homo sapiens, and many other species, beauty is the intelligent verdict of a complex but mostly unconscious computation. Each time you encounter a person, your senses automatically inspect dozens, perhaps hundreds, of telltale clues—all in a fraction of a second. These clues, meticulously selected through eons of evolution, inform you about one thing: reproductive potential. That is, could this person have, and raise, healthy offspring? Of course, explicit thoughts about this question, and explicit clues to a verdict, are not what you typically experience in that encounter. Instead you experience just the verdict itself—as a feeling that varies from hot to not. That feeling, that executive summary of a painstaking investigation, is the beauty in the eye of the beholder.

Which gives the lie to the idea that beauty is a whim of the beholder. To the contrary, it is the consequence of unconscious inferences within the beholder, inferences that were crafted over millennia by the logic of natural selection: if the inferences too often delivered a verdict of hot when they should have said not, or vice versa, then the beholder would too often prefer mates who were less likely to raise healthy offspring. In this case, the beholder’s misguiding genes, and their faulty inferences, would be less likely to pass into the next generation. In short, if genes get beauty wrong, they tend to go extinct. This is the pitiless logic of natural selection.

It’s all about struggles between genes. Which is to say, it’s all about fitness—the central concept of evolution by natural selection. Genes that are more adept at elbowing their way into the next generation are said to be fitter. Even a slight excess of talent in the art of the elbow can allow a gene to proliferate across generations and eradicate competitors of but moderate talent. Oscar Wilde understood this logic well. “Moderation,” he wrote, “is a fatal thing. . . . Nothing succeeds like excess.”

Beauty por Manuel Fraga está licenciado bajo una Licencia Creative Commons Atribución 4.0 Internacional.

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