Matt Ridley

would be odd if it were not. A suggestive hint comes from Trinidad where small fish called guppies vary in color according to the stretch of water they inhabit: Two American scientists proved that in those types of guppies in which the males are brightest orange in color, the females show the strongest preference for orange males. 16

This female preference for male ornaments can actually be a threat to the survival of the males: The scarlet-tufted malachite sunbird is an iridescent green bird that lives high on the slopes of Mount Kenya where it feeds on the nectar of flowers and on insects that it catches on the wing. The male has two long tail streamers, and females prefer the males with the longest streamers. By lengthening the tail streamers of some males, shortening those of others, adding weight to those of a third group, and merely adding rings of similar weight to the legs of a fourth, two scientists were able to prove that female-preferred tail streamers are a burden to their bearers. The ones with lengthened or weighted tails were worse at catching insects; the ones with shortened tails were better; the ones with only rings on their legs were as good as normal.'

Females choose; their choosiness is inherited; they prefer exaggerated ornaments; exaggerated ornaments are a burden to males. That much is now uncontroversial: Thus far Darwin was right.

DESPOTIC FASHIONS

The question Darwin failed to answer was why: Why on earth should females prefer gaudiness in males? Even if the 'preference'

was entirely unconscious and was merely an instinctive response to the superior seduction technique of gaudy males, it was the evolution of the female preference, not the male trait, that was hard to explain.

Sometime during the 1970s it began to dawn on people that a perfectly good answer to the question had been available since 1930. Sir Ronald Fisher had suggested then that females need no better reason for preferring long tails than that other

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THE PEACOCK S TALE

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females also prefer long tails. At first such logic sounds suspiciously circular, but that is its beauty. Once most females are choosing to mate with some males rather than others and are using tail length as the criterion—a big once, granted, but we'll return to that—then any female who bucks the trend and chooses a short-tailed male will have short-tailed sons. (This presumes that the sons inherit their father 's short tail.) All the other females are looking for long-tailed males, so those short-tailed sons will not have much success: At this point, choosing long-tailed males need be no more than an arbitrary fashion; it is still despotic. Each peahen is on a treadmill and dare not jump off lest she condemn her sons to celibacy. The result is that the females ' arbitrary preferences have saddled the males of their species with ever more grotesque encumbrances. Even when those encumbrances themselves threaten the life of the male, the process can continue—as long as the threat to his life is smaller than the enhancement of his breeding success: In Fisher 's words: ' The two characteristics affected by such a process, namely plumage development in the male and sexual preference in the female, must thus advance together, and so long as the process is unchecked by severe counter-selection, will advance with ever-increasing speed. 'i '

Polygamy, incidentally, is not essential to the argument.

Darwin noticed that some monogamous birds have very colorful males: mallards, for example, and blackbirds. He suggested that it would still benefit males to be seductive and so win the first females that are ready to breed, if not the most, and his conjecture has largely been borne out by recent studies. Early-nesting females rear more young than late-nesting ones, and the most vigorous songster or gaudiest dandy tends to catch the early female. In those monogamous species in which both males and females are colorful (such as parrots, puffins, and peewits) there seems to be a sort of mutual sexual selection at work: Males follow a fashion for picking gaudy females and vice versa. 19

Notice, though, that in the monogamous case the male is choosing as well as seducing. A male tern will present his intended with fish, both to feed her and to prove that he can fish well

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The Red Quern

enough to feed her babies. If he is choosing the earliest female to arrive and she is choosing the best fisherman, they are both employing eminently sensible criteria. It is bizarre even to suggest that choice plays no part in their mating: From terns to peafowl, there is a kind of continuum of different criteria. A hen pheasant, for example, who will get no help from a cock in rearing her young, happily chooses to ignore a nearby cock who is unmated to join the harem of a cock who already has several wives: He runs a sort of protection racket within his territory, guarding his females while they feed in exchange for sexual monopoly over them: The best protector is more use to her than a faithful house-husband: A peahen, on the other hand, does not even get such protection: The peacock provides her with nothing but sperm: 20

Yet there is a paradox here. In the tern 's case, choosing a poor male is a disastrous decision that will leave her chicks liable to starve. In the hen pheasant 's case, choosing the less effective harem defender will apparently leave her inconvenienced. In the peahen 's case, picking the poorest male will leave her hardly affected at all: She gets nothing practical from her mate, so it seems there is nothing to be lost. You would expect, therefore, that the choice would be made most carefully by the tern and least carefully by the peahen.

Appearances suggest the exact opposite. Peahens survey several males and take their time over their decision, allowing each to parade his tail to best advantage. What is more, most of the peahens choose the same male. Terns mate with little fuss. Females are the most choosy where the least seems to be at stake. 21

RUNNING OUT OF GENES

Least at stake? One very important thing is at stake in the peafowl case: a bunch of genes. Genes are the only thing a peahen gets from a peacock, whereas a female tern gets tangible help from the male as well. A tern must demonstrate only paternal proficiency; a peacock must demonstrate that he has the best genes on offer.

Peacocks are among the few birds that run a kind of market

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in seduction techniques, called a 'lek,' after the Swedish word for play. Some grouse, several birds of paradise and manakins, plus a number of antelope, deer, bats, fish, moths, butterflies, and other insects also indulge in lekking. A lek is a place where males gather in the breeding season, mark out little territories that are clustered