This looked to be fatal to the whole Fisher idea, and there was brief interest in another version of it (which is known as the 'sexy-son '
theory) that suggested sexy husbands made bad fathers—a clear cost to being a choosy female:'
Luckily, another mathematical insight came to the rescue.
The genes that cause the elaborate ornament or long tail to appear are subject to random mutation. The more elaborate the ornament, the more likely that a random mutation will make the ornament less elaborate, not more. Why? A mutation is a wrench thrown into the genetic works: Throwing a wrench into a simple device, such as a bucket, may not alter its function much, but throwing a wrench into a more complicated device, such as a bicycle, will almost certainly make it less good as a bicycle: Thus, any change in a gene will tend to make the ornament smaller, less symmetrical, or less colorful: This 'mutational bias ' is sufficient, according to the mathematicians, to make it worth the female 's while to choose an ornamented male because it means that any defect in the ornament might otherwise be inherited by the sons; by choosing the most elaborate ornament she is choosing the male with the fewest mutations: The mutational bias is also sufficient, perhaps, to defeat the
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central conundrum that we set the theories earlier—the fact that if the best genetic cream of the cream is taken off each generation, there will soon be no separability left in the cream. Mutational bias keeps turning some,of the cream back into milk.'
The result of a decade of mathematical games, then, has been 'to prove that the Fisherians are not wrong. Arbitrary ornaments can grow elaborate for no other reason than that females discriminate between males and end up following arbitrary fashions; and the more they discriminate, the more elaborate the ornaments become: What Fisher said in 1930 was right, but it left a lot of naturalists unconvinced for two reasons: First, Fisher assumed part of what he set out to prove: That females are already choosy is crucial to the theory: Fisher himself had an answer for this, which was that initially females chose long-tailed males for more utilitarian reasons—for example, that it indicated their superior size or vigor: This is not a foolish idea; after all, even the most monogamous species, in which every male wins a female (such as terns), are choosy. But it is an idea borrowed from the enemy camp: And the Good-geners can reply: 'If you admit that our idea works initially, why rule it out later on? '
The second reason is more mundane. Proving that Fisher 's runaway selection could happen and the ornament get bigger with ever-increasing speed does not prove that it does happen: Computers are not the real world: Nothing could satisfy the naturalists but an experiment, one demonstrating that the sexiness of sons drove the evolution of an ornament:
Such an experiment has never been devised, but those, like me, with a bias toward the Fisherians find several lines of argument fairly persuasive: Look around the world and what do you see? You see that the ornaments we are discussing are nothing if not arbitrary: Peacocks have eyes in their train; sage grouse have inflatable air sacs and pointed tails; nightingales have melodies of great variety and no particular pattern; birds of paradise grow bizarre feathers like pennants; bower birds collect blue objects. It is a cacophony of caprice and color: Surely if sexually selected ornaments told a tale of their owner's vigor, they would not be so utterly random.
One other piece of evidence seems to weigh in the balance on the side of Fisher—the phenomenon of copying. If you watch a lek carefully, you see that the females often do not make up their own minds individually; they follow one another. Sage grouse hens are more likely to mate with a cock who has just mated with another hen. In black grouse, which also lek, the cocks tend to mate several times in a row if at all. A stuffed female black grouse (known in this species as a greyhen) placed in a male 's territory tends to draw other females to that territory—though not necessarily causing them to mate. De In guppy fish, females that have been allowed to see two males, one of which is already courting a female, subsequently prefer that male to the other even if the female that was being courted is no longer present.'
Such copying is just what you would expect if Fisher was right because it is fashion-following for its own sake. It hardly matters whether the male chosen is the 'best' male; what counts is that he is the most fashionable, as his sons will be. If the Good-geners are right, females should not be so influenced by each other 's views. There is even a hint that peahens try to prevent one another from copying, which would also make sense to a follower of Fisher.'° If the goal is to have the sexiest son in the next generation, then one way of doing that is to mate with the sexiest male; a second way is to prevent other females from mating with the sexiest male.
ORNAMENTAL HANDICAPS
If females choose males for the sexiness of their future sons, why shouldn 't they go for other genetic qualities, too? The Good-geners think that beauty has a purpose. Peahens choose genetically superior males in order to have sons and daughters who are equipped to survive as well as equipped to attract mates.
The Good-geners can marshal as much experimental support as the Fisherians. Fruit flies given a free choice of mate produce young that prove tougher in competition with the young of THE PEACOCKS TALE
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those not allowed to choose.' Female sage grouse, black grouse, great snipe, fallow deer, and widow birds all seem to prefer the males on their leks that display most vigorously. 32 If a stuffed greyhen is put on the boundary between two blackcocks ' dancing grounds, the two males fight over the right to monopolistic necrophilia. The winner is usually the male who is most attractive to females, and he is also more likely to survive the next six months than the other male. This seems to imply that attracting females is not the only thing he is good at; he is also good at surviving.' The brighter red a male house finch is, the more popular he is with the females; but he is also a better father—he provides more food for the babies—and will live longer because he is genetically more disease-resistant: By choosing the reddest male on offer, females are therefore getting superior survival genes as well as attractiveness genes.34
It is hardly surprising to find that the males best at seduction tend to be the best at other things as well; it does not prove that females are seeking good genes for their offspring. They might be avoiding feeble males lest they catch a virus from them: Nor do such observations damage the idea that the most important thing a sexy male can pass on to his sons is his sexiness—the Fisher idea.
They merely suggest that he can also pass on other attributes.
Consider, though, the case of Archbold 's bowerbird, which lives in New Guinea. As in other bowerbirds, the male builds an elaborate bower of twigs and ferns and therein tries to seduce females: The female inspects the bower and mates with the male if she likes the workmanship and the decorations, which are usually objects of one unusual color. What is peculiar about Archbold 's bowerbird is that the best decorations consist of feathers from one
