The Red Queen_ Sex and the Evolution of Human Nature - Matt Ridley [82]
Of Mozart and Grackle Song
Down the corridor from Ryan at the University of Texas is Mark Kirkpatrick, who is prepared to upset even more apple-carts. Kirkpatrick is acknowledged as one of those who understands sexual selection theory most thoroughly; indeed he was one of those who made Fisher’s idea mathematically respectable in the early 1980s. But he now refuses to accept that we must choose between Fisher and Zahavi. He does so partly because of what Ryan has discovered.
This does not mean Kirkpatrick rejects female choice, as Julian Huxley did. Whereas Huxley thought males did the choosing by fighting among themselves, Kirkpatrick prefers to believe that in many species the females do choose but their preferences do not evolve. They merely saddle the males with their own idiosyncratic tastes.
Both Good-genes and Fisher theories are obsessed with trying to find a reason for exuberant display that benefits the male. Kirkpatrick looks at it from the female’s point of view. Suppose, he says, that peahens’ preferences have indeed saddled peacocks with their tails. Why must we explain these female preferences only in terms of the effects on their sons and daughters? Might the peahens not have perfectly good direct reasons for choosing as they do? Might their preferences not be determined by something else entirely? He thinks ‘other evolutionary forces acting on the preferences will overwhelm the Good-genes factor and often establish female preferences for traits that decrease male survival’.75
Two recent experiments support the idea that females simply have idiosyncratic tastes that have not evolved. Male grackles – blackish birds of medium size – sing only one kind of song. Female grackles prefer to mate with males that sing more than one kind of song. William Searcy of the University of Pittsburgh discovered why. He made use of the fact that a female grackle will go up to singing loudspeakers and adopt a soliciting posture as if waiting to be mated. Her tendency to do so, however, declines as she gets bored with the song. Only if the loudspeaker starts singing a new song will her soliciting start afresh. Such ‘habituation’ is just a property of the way brains work; our senses, and those of grackles, notice novelty and change, not steady states. The female preference did not evolve: it just is that way.76
Perhaps the most startling discovery in sexual-selection theory was Nancy Burley’s work on zebra finches in the early 1980s. She was studying how these small Australian finches choose their mates, and to make it easier she kept them in aviaries and marked each one with a coloured ring on its leg. After a while she noticed something odd: the males with red rings seemed to be preferred by the females. Further experiments proved that the rings were drastically affecting the ‘attractiveness’ of both males and females. Males with red rings were attractive; those with green rings unattractive; females with black or pink rings were preferred; those with light blue rings disliked. It was not just rings. Little paper hats glued to the birds’ heads also altered their attractiveness. Female zebra finches have a rather simple rule for assessing potential mates: the more red he has on his body (or the less green, which comes to the same thing given that red and green are seen as opposites by the brain), the more attractive he is.77
If females have an existing aesthetic preference, it is only logical that males will evolve that exploit that preference. For example, it is possible that the ‘eyes’ on a peacock’s tail are seductive to peahens because they resemble huge versions of real eyes. Real eyes are visually arresting – perhaps even hypnotic – to many kinds of animals and the sudden appearance of many huge staring eyes may induce a state of mild hypnosis in the peahen, which allows the peacock to lunge at her.78 This would be consistent with the common discovery that ‘supernormal stimuli’ are often more effective than normal ones. For example, many birds prefer a ridiculous, giant egg in their