The result is that males compete for the attention of females, which means that males have a greater opportunity to leave large numbers of offspring than females and a greater risk of not breeding at alclass="underline" Males act as a kind of genetic sieve: Only the best males get to breed, and the constant reproductive extinction of bad males constantly purges bad genes from the population.' From time to time it has been suggested that this is the "purpose" of males, but that commits the fallacy of assuming evolution designs what is best for the species:
The sieve works better in some species than in others: Elephant seals are so severely sieved that in each generation a handful of males father all the offspring: Male albatrosses are so faithful to their single wives that virtually every male that reaches the right age will breed. Nonetheless, it is fair to state that in the matter of choosing mates, males are usually after quantity and females after quality: In the case of a bird such as a peacock, males will go through their ritual courtship display for any passing female; females will mate with only one male, usually the one with the most elaborately decorated taiclass="underline" Indeed, according to sexual selection theory, it is the female 's fault that the male has such a ridiculous tail at alclass="underline" Males evolved long tails to charm females: Females evolved the ability to be charmed to be sure of picking the best males.
This chapter is about a kind of Red Queen contest, one that resulted in the invention of beauty: In human beings, when all
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practical criteria for choosing a mate—wealth, health, compatibility, fertility—are ignored, what is left is the apparently arbitrary criterion of beauty. It is much the same in other animals. In species where the females get nothing useful from their mates, they seem to choose on aesthetic criteria alone:
ORNAMENTS AND CHOOSINESS
To put it in human terms, we are asking of animals (as we later will of human beings): Are they marrying for money, for breeding, or for beauty? Sexual selection theory suggests that much of the behavior and some of the appearance of an animal is adapted not to help it survive but to help it acquire the best or the most mates.
Sometimes these two—survival and acquiring a mate—are conflict-ing goals: The idea goes back to Charles Darwin, though his thinking on the matter was uncharacteristically fuzzy: He first touched on the subject in On the Origin of Species but later wrote an entire book about it: The Descent of Man and Selection in Relation to Sex:'
Darwin 's aim was to suggest that the reason human races differed from one another was that for many generations the women in each race had preferred to mate with men who looked, say, black or white. In other words, at a loss to explain the useful-ness of black or white skin, he suspected instead that black women preferred black men and white women preferred white men—and posited this as cause rather than effect: Just as pigeon fanciers could develop breeds by allowing only their favorite strains to reproduce, so animals could do the same to one another through selective mate choice.
His racial theory was almost certainly a red herring,' but the notion of selective mate choice was not: Darwin wondered if selective "breeding" by females was the reason that so many male birds and other animals were gaudy, colorful, and ornamented.
Gaudy males seemed a peculiar result of natural selection since it was hard to imagine that gaudiness helped the animal to survive: In fact, it would seem to be quite the reverse: Gaudy males should be more conspicuous to their enemies.
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THE PEACOCK S TALE
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Taking the example of the peacock, with its great tail decked with iridescent eyes, Darwin suggested that peacocks have long tails (they are not actually tails but elongated rump feathers that cover the tail) because peahens will mate only with peacocks that have long tails. After all, he observed, peacocks seem to use their tail when courting females. Ever since then the peacock has been the crest, mascot, emblem, and quarry of sexual selection: Why should peahens like long tails? Darwin could only reply: Because I say so. Peahens prefer long trains, he said, because of an innate aesthetic sense—which is no answer at all. And peahens choose peacocks for their tails rather than vice versa because, sperm being active and eggs passive, that is usually the way of the world: Males seduce, females are seduced.
Of all Darwin's ideas, female choice proved the least persuasive: Naturalists were quite happy to accept the notion . that male weapons, such as antlers, could have arisen to help males in the battle for females, but they instinctively recoiled at the frivo-lous idea that a peacock 's tail should be there to seduce peahens.
They wanted, rightly, to know why females would find long tails sexy and what possible value they could bring the hens: For a century after he proposed it, Darwin 's theory of female choice was ignored while biologists tied themselves in furious knots to come up with other explanations. The preference of Darwin 's contempo-rary, Alfred Russel Wallace, was initially that no ornaments, not even the peacock 's tail, required any explanation other than that they served some useful purpose of camouflage. Later he thought they were the simple expression of surplus male vigor. Julian Huxley, who dominated the discussion of the matter for many years, much preferred to believe that almost all ornaments and ritual displays were for intimidating other males: Others believed that the ornaments were aids to females for telling species apart, so that they chose a mate of the right species.' The naturalist Hugh Cott was so impressed by the bright colors of poisonous insects that he suggested all bright colors and gaudy accessories were about warn-ing predators of dangers: Some are. In the Amazon rain forest the butterflies are color-coded: yellow and black means distasteful, blue and green means too quick to catch.' In the 1980s a new version of
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this theory was adapted to birds, suggesting that colorful birds are the fastest fliers and are flaunting the fact to hawks and other predators: I 'm fast, so don 't even think of trying to chase me: When a scientist put stuffed male and female pied flycatchers out on perches in a wood, it was the dull females that were attacked first by hawks, not the colorful males.' Any theory, it seemed, was preferred to the idea of female preference for male beauty: Yet it is impossible to watch peacocks displaying and not come away believing that the tail has something to do with the seduction of peahens. After all, that was how Darwin got the idea in the first place; he knew that the gaudiest plumes of male birds were used in courting females and not in other activities: When two peacocks fight or when one runs away from a predator, the tail is kept carefully folded away.'
TO WIN OR TO WOO
It took more than this to establish the fact of female choice. There were plenty of diehards who followed Huxley in thinking courtship was all a matter of competition between males. "Where female choice has been described, it plays an ancillary, and probably less significant, role than competition between males, " wrote British biologist Tim Halliday as late as 1983: 1° Just as a female red deer accepts her harem master, who has fought for the harem, so perhaps a peahen accepts that she will mate with the champion male.
In one sense the distinction does not matter much. Peahens that all pick the same cock and red deer hinds that indifferently submit to the same harem master both end up "choosing " one male from among many. In any case, the peahens ' "choice" may be no more voluntary or conscious than the hinds ': The peahens have merely been seduced rather than won. They may have been seduced by the display of the best male without ever having given the matter a conscious thought—let alone realized that what they were doing was "choosing: " Think of human analogies. Two caricatured cavemen who fought to the death so that the winner could sling the THE PEACOCKS TALE