present, a female roach probably can as well: This pattern results from different kinds of sex hormones; one can be raised in concentration only at the expense of leaving the roach vulnerable to one kind of parasite; the other can be raised only at the expense of lowering defenses against 59
another kind of parasite:
If cockerels ' wattles and roach tubercules are honest signals, so presumably are songs: A nightingale that can sing loud and long must be in vigorous health, and one that has a large repertoire of different melodies must be experienced or ingenious, or both. An energetic display such as the pas de deux of a pair of male manakins may also be an honest signal: A bird that merely shows its feathers, such as a peacock or a bird of paradise, might be a cheat whose strength has been sapped by bad habits since he grew the plumes: After all, peacock feathers still shine brightly when their owner is dead and stuffed. Perhaps it is no surprise, then, that most male birds do not molt just before the breeding season but adopt their spring plumage the autumn before. They have to keep it tidy all winter: The very fact that a male has looked after his plumes for six months tells a female something about his enduring vigor: Bill Hamilton points out that white fluffy feathers around a bird's rear end, which are common in grouse of various kinds, must be especially hard to keep clean if the bird has diarrhea. b°
Zahavi certainly believed that honesty was a prerequisite of
handicaps, and vice versa. To be honest, he thought, an ornament must be costly; otherwise it could be used to cheat. A deer cannot grow large antlers without consuming five times its normal daily intake of calcium; a pupfish cannot be iridescent blue unless it is genuinely in good condition, a fact that will be tested by other male fish in fights. On the assumption that anybody who refuses to play the game and use an honest signal must have something to hide, males are likely to find themselves dragged into honest displays. Therefore, display ornaments are examples of 'truth in advertising. '61
All this is very logical, but in about 1990 it started to make one group of biologists uneasy. They had an instinctive aversion to the idea that sexual advertising is about the truth because they knew that television advertising is not about passing on information; it is about manipulating the viewer. In the same way, they argued, all animal communication is about manipulating the receiver.
The first and most eloquent (manipulative?) champions of this view were two Oxford biologists, Richard Dawkins and John Krebs: According to them, a nightingale does not sing to inform potential mates about himself; he sings to seduce them. If that means lying about his true prowess, so be it: 62 Perhaps an ice cream advertisement is honest in a simplistic sense because it gives the name of the brand, but it is not honest in implying that sex is sure to follow after every spoonful. Such a crude lie can surely be perceived by that genius of the animal kingdom, humans. But it is not.
Advertising works. Brand names are better known if they are advertised with sexy or alluring pictures, and better-known brands sell better. Why does it work? Because the price the consumer would have to pay in ignoring the subliminal message is just too high. It is better to be fooled into buying the second-best ice cream than go to the bother of educating yourself to resist the salesmanship.
Any peahens reading this might begin to recognize their dilemma. For they, too, may be fooled by the male's display into buying the second-best male: Remember, the lek paradox argues that there is little to choose between males on a lek anyway because they were all fathered by the same few males in the previous genera-THE PEACOCKS TALE
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tion. So two theories—truth in advertising and dishonest manipulation—seem to come to opposite conclusions. Truth in advertising concludes that females will discover a cheating seducer; dishonest manipulation concludes that males will seduce females against their better judgment.
WHY DO YOUNG WOMEN HAVE NARROW WAISTS?
Marian Dawkins and Tim Guilford of Oxford have recently suggested a resolution to this conundrum. As long as detecting the dishonesty in the signal is costly to the female, it might not be worth her while to do so. In other words, if she has to risk her life seeking out and comparing many males to ensure that she has chosen the best one, then the marginal advantage she gains by picking the best one is outweighed by the risk she has run. It is better to let herself be seduced by a good one than to have the best become the enemy of the good. After all, if she cannot easily distinguish the truthful from the dishonest badge of quality, then other females will not, either, and so her sons will not be punished for any dishonesty they inherit from their father.'
A startling example of this sort of logic comes from a controversial theory about human beings that was developed a few years ago by Bobbi Low and her colleagues at dhe University of Michigan: Low was looking to explain why young women have fat on their breasts and buttocks more than on other parts of their bodies. The reason this requires explaining is that young women are different from other human beings in this respect. Older women, young girls, and men of all ages gain fat on their torsos and limbs much more evenly. If a woman of twenty or so gains weight, it largely takes the form of fat on the breasts and buttocks; her waist can remain remarkably nartow.
So much is undisputed fact. What follows is entirely conjecture, and it was a conjecture that caused Low a good deal of sometimes vicious (and mostly foolish) criticism when she published the idea in 1987:
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Twenty-year-old women are in their breeding prime; therefore, the unusual pattern of fat distribution might be expected to be connected with getting a mate or bearing children. Standard explanations concern the bearing of children; for example, fat is inconvenient if it competes for space about the waist with a fetus.
Low 's explanation concerns the attraction of mates and takes the form of a Red Queen race between males and females. A man looking for a wife is likely to be descended from men who found two things attractive (among many others): big breasts, for feeding his children, and wide hips, for bearing them. Death during infancy due to a mother 's milk shortage would have been common before modern affluence—and still is in some parts of the world. Death of the mother and infant from a birth canal that was too narrow must also have been common. Birth complications are peculiarly frequent in humans for the obvious reason that the head size of a baby at birth has been increasing quickly in the past 5 million years. The only way birth canals kept pace (before Julius Caesar 's mother was cut open) was through the selective death of narrow-hipped women.
Grant, then, that early men may have preferred women with relatively wide hips and large breasts. That still does not explain the gaining of fat on breasts and hips; fat breasts do not produce more milk than lean ones, and fat hips are no farther apart than lean ones of the same bone structure. Low thinks women who gained fat in those places may have deceived men into thinking they had milkful breasts and wide hip bones: Men fell for it—
