using sexy pictures, airplane tickets using couples walking hand in hand on beaches, instant coffee using romance, and cigarettes using cowboys.
When a man wants to seduce a woman, he does not send her a copy of his bank statement but a pearl necklace. He does not send her his doctor 's report but lets slip that he runs twenty miles a week and never gets colds. He does not tell her what degree he got but instead dazzles her with wit: He does not display testa-ments to how thoughtful he is but sends her roses on her birthday.
Each gesture has a message: I 'm rich, I'm fit, I'm clever, I 'm nice.
But the information is packaged to be more seductive and more effective, just as the message 'Buy my ice cream ' catches the eye when it is accompanied by a picture of two good-looking people seducing each other.
In courtship, as in the world of advertising, there is a discrepancy of interests between the buyer and the seller: The female needs to know the truth about the male: his health, wealth, and genes. The male wants to exaggerate the information: The female wants, the truth; the male wants to lie: The very word seduction implies trickery and manipulation.'
Seduction therefore becomes a classic Red Queen contest, although this time the two protagonists are male and female, not host and disease: Zahavi 's handicap theory, as explored by Hamilton and Zuk, predicted that honesty would eventually prevail and males who cheat would be revealed: This is because the handicap is the female's criterion of choice for the very reason that it reveals the male 's state of health.
The red jungle fowl is the ancestor of the domestic chicken.
Like a farmyard rooster, the cock is equipped with a good many THE PEACOCK ' S TALE
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ornaments that his mate does not share: long, curved tail feathers, a bright ruff around the neck, a red comb on the crown of his head, and a loud dawn call, to name the most obvious. Marlene Zuk wanted to find out which of these mattered to female jungle fowl, so she presented sexually receptive hens with two tethered males and examined which they chose. In some of the trials one of the cocks was reared with a roundworm infection in his gut, which affected his plumage, beak, and leg length very little but showed clearly in his comb and eye color, both of which were less colorful than in healthy males. Zuk found that hens preferred cocks with good combs and eyes but paid less attention to plumage. She failed to make hens go for males with fake red elastic combs on their heads, however; they found them too bizarre. Nonetheless, it was clear that hens paid most attention to the most health informative feature of a cock.'
Zuk knew that poultry farmers, too, observe the comb and wattles of a cockerel to judge his health. What intrigued her was the idea that the wattles were more 'honest ' about the state of a cockerel than his feathers. Many birds, especially in the pheasant family, grow fleshy structures about their faces to emphasize during display: Turkeys grow long wattles over their beaks, pheasants have fleshy red 'roses ' on their faces, sage grouse bare their air sacs, and tragopans have expandable electric blue bibs beneath their chins.
A cockerel's comb is red because of the carotenoid pigments in it. A male guppy fish is rendered orange by carotenoids also, and a housefinch ' s and a flamingo ' s red plumage also depends on carotenoids. The peculiar thing about carotenoids is that birds and fish cannot synthesize them within their own tissues; they extract them from their food—from fruit, shellfish, or other plants and invertebrates. But their ability to extract carotenoids from their food and deliver it to their tissues is greatly affected by certain parasites. A cockerel affected by the bacterial disease coccidiosis, for example, accumulates less carotenoid in his comb than a healthy cockerel—even when both animals have been fed equal quantities of carotenoid: Nobody knows exactly why the parasites have this
specific biochemical effect, but it seems to be unavoidable and is therefore extremely useful to the female: The brightness of carotenoid-filled tissues is a visible sign of the levels of parasite infection. It is not surprising that red and orange are common colors in fleshy ornaments used in display, such as the combs, wattles, and lappets of pheasants and grouse.'
The size and brightness of such combs may be
The hormone itself seems to lower his resistance to parasites:'
Once again nobody knows why, but cortisol, the ' stress' hormone that is released into the bloodstream during times of emotional crisis, also has a marked effect on the immune system. A long study of cortisol levels in children in the West Indies revealed that the children are much more likely to catch an infection shortly after their cortisol levels have been high because of family tension or other stress:' Cortisol and testosterone are both steroid hormones, and they have a remarkably similar molecular structure. Of the five biochemical steps needed to make cholesterol into either cortisol or testosterone, only the last two steps are different: S6 There seems to be something about steroid hormones that unavoidably depresses immune defense. This immune effect of testosterone is the reason that men are more susceptible to infectious diseases than women, a trend that occurs throughout the animal kingdom. Eunuchs live longer than other men, and male creatures generally suffer from higher mortality and strain. In a small Australian creature called the marsupial mouse, all the males contract fatal diseases during the frantic breeding season and die. It is as if male animals have a finite sum of energy that they can spend on testosterone or immunity to disease, but not both at the same time.'
The implication for sexual selection is that it does not pay to lie: Having sex-hormone levels that are too high increases the size of your ornaments but makes you more vulnerable to parasites, which are revealed in the state of those ornaments. It is possible
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that it works in the other direction: The immune system suppresses the production of testosterone. In Zuk 's words, 'Males are thus necessarily more vulnerable to disease as they acquire the accoutrements of maleness. ''
The best proof of these conjectures comes from a study of roach, which are small fish with reddish fins, in the Lake of Biel in Switzerland. Male roach grow little tubercules all over their bodies during the breeding season, which seem to stimulate females during courtship as the fish rub against each other. The more parasites a male has, the fewer tubercules he grows. It is possible for a zoologist to judge, just from a male 's tubercules, whether he is infested with a roundworm or a flatworm. The implication follows: If a zoologist can deduce which parasite is
