Males with red rings were attractive; those with green rings unattractive; females with black or pink rings were preferred; those with light blue rings disliked: It was not just rings: Little paper hats glued to the birds ' heads also altered their attractiveness: Female zebra finches have a rather simple rule for assessing potential mates: The more red he has on his body (or the less green, which comes to the same thing given that red and green are seen as opposites by the brain), the more attractive he is. 7b If females have an existing aesthetic preference, it is only logical that males will evolve to exploit that preference: For example, it is possible that the "eyes" on a peacock 's tail are seductive to peahens because they resemble huge versions of real eyes. Real eyes are visually arresting—perhaps even hypnotic—to many kinds of animals, and the sudden appearance of many huge staring eyes may induce a state of mild hypnosis in the peahen, which allows the peacock to lunge at her:" This would be consistent with the common discovery that "supernormal stimuli " are often more effective than normal ones. For example, many birds prefer a ridiculous giant
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egg in their nest to a normal one; a goose will prefer to try to sit on an egg the size of a soccer ball than one of normal size: It is as if their brains have a program that says "like eggs, " and the bigger the egg, the more it likes them. So perhaps the bigger the eye-spot, the more attractive or startling it is for a peahen, and the mile has simply exploited this by evolving lots of giant eyes without any evolutionary change in the female 's preference. 7e HANDICAPPED ADVERTISERS
Andrew Pomiankowski of London accepts much of what Ryan and Kirkpatrick say but parts company with them on the matter of female choice. He says that what they are considering is merely a constraint that channels the male ' s trait into the preferred direction of the female's sensory bias. But that does not mean the exaggeration happens without the female 's preference changing. It is almost impossible to see how females could avoid the Fisher effect as the male 's ornament gets more exaggerated generation by generation. The female who is most discriminating picks the sexiest male and so has the sexiest sons; the one who has the sexiest sons has the most granddaughters. So females get more and more discriminating and more and more difficult to seduce or hypnotize: "The crucial question, " wrote Pomiankowksi, "is not whether sensory exploitation has been involved but why females have allowed themselves to be exploited. " Besides, it is an impoverished view of selection to believe that a frog 's ear can be tuned for detecting predators but not tuned simultaneously and differently to choosing males."
Thus, it is possible to argue with Ryan and Kirkpatrick that male courtship extravagances reflect the innate tastes of females without abandoning the idea that those tastes are of use to the females in that they select the best genes for the next generation. A peacock 's tail is, simultaneously, a testament to naturally selected female preferences for eyelike objects, a runaway product of despotic fashion among peahens, and a handicap that reveals its posses-
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sor 's condition. Such tolerant pluralism is not to everybody 's taste, but Pomiankowski insists it does not stem from misguided desire to please everybody: On a paper napkin in an Indian restaurant one day he sketched out for me a plausible account of all the sexual selection theories working in concert.
Each male trait begins as a chance mutation: If it happens to hit a sensory bias of the female, it starts to spread. As it spreads, the Fisher effect takes over, and both the trait and the preference are exaggerated: Eventually the point is reached where the trait has spread to all males, and there is no point in females following the fashion anymore. It starts to fade again, under pressure from the fact that there is now a cost to female choice: if nothing else, it is a waste of females ' time and effort to compare different males: The Fisher effect fades more slowly when that cost is small—for example, in lekking species where the males can all be viewed at once.
But some traits do not fade because it so happens that they reflect the underlying health of their possessors—they change color if the male is infected with parasites, for example. And therefore females do not stop choosing the best males at all. They keep picking (or being seduced by) the fanciest male because if they do, they will have disease-resistant offspring: In other words, condition-reflecting traits will not be the only ones brought to an exaggerated state, but they will be the ones that persist the longest: And all the Fisher-exaggerated traits remain in lekking species as well because the cost of choosing is so smalclass="underline" The most promiscuous species end up a collage of different handicaps, ornaments, and gaudy blotches.
Pomiankowski has since begun to confirm his intuition (based on the symmetry idea discussed earlier) that multiple traits on polygamous birds, such as the many adornments of a peacock, are Fisher ornaments, while single features on monogamous birds, such as the swallow 's forked tail, are Good-gene ornaments, or condition-revealing handicaps. 80
The next time you visit a zoo in the spring, try to watch a male Lady Amherst pheasant from China posturing before a hen.
He is a riot of color: His face is pale green, his crest scarlet, his throat iridescent green, his back emerald, his rump orange, and his
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belly pristine white: Around his neck is a white ruff trimmed with black, and at the base of his tail are five pairs of vermillion feathers: His tail, white barred with black, is longer than his body: A dull or damaged feather would stand out anywhere on his body: He is one great advertisement for good genes, handicapped by the need to keep clean, healthy, and out of danger, a walking illustration of his mate's evolved sensory biases:
THE HUMAN PEACOCK
The antics of peacocks and guppies are interesting enough in themselves to naturalists; to students of evolution they are intriguing as test cases; but to the rest of us what makes them worth studying is pure self-centeredness: We want to know what lessons they teach us about human affairs: Are some men successful with women because their appearance sends an honest signal of their handicapping good genes and their ability to resist disease?
The idea is ridiculous: Men succeed with women for much more varied and subtle reasons: They are kind or clever or witty or rich or good-looking or just available. Humans are simply not a lekking species. Men do not gather in groups to display for passing women: Most men do not abandon women immediately after copulation: Men are not equipped with gorgeous ornaments or stereotyped courtship rituals, however it may look in the average discotheque. When a woman chooses a man to mate with, she is less concerned with whether he can father sexy sons or disease-resistant daughters than whether he would make a good husband. A man choosing a wife uses equally mundane considerations, though he is perhaps more of a sucker for beauty: Both genders use criteria that bear on parental abilities. They are more like terns, who choose mates that can fish well, than sage grouse hens, who copy one another 's choice of a fast-displaying male. So the Red Queen race between the genders over seduction and sales resistance that follows from pure Good-gene choice does not happen: And yet we cannot be so categoricaclass="underline" There are species of THE PEACOCK ' S TALE
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mammal in which the effects of sexual selection are few and small.
It is hard to argue that the average rat has been endowed with conspicuous display'ornaments by the preferences of ancestral females: Even our closest relatives, the chimpanzees, are little touched by the effects of female choice: Males look much like females, and courtship is somewhat simple. But we should pause before dismissing the effects of sexual selection on human beings. People, after all, are universally interested in beauty. Lipstick, jewelry, eye shad-ow, perfume, hair dyes, high heels—people are just as willing to exaggerate or lie about their sexually alluring traits as any peacock or bowerbird: And as the list above makes clear, it seems as if men seek female beauty rather more than women seek male beauty. The human being, in other words, may be the victim of generations of male choice even more than female choice: If we are to apply sexual selection theory to man, it is male choice for female genes that we should examine. But it makes little difference: When one gender is being choosy, all the consequences of sexual selection theory inevitably flow: It is quite possible, even likely, as the next few chapters will reveal, that some parts of the human body and psyche have been sexually selected.