The Red Queen_ Sex and the Evolution of Human Nature - Matt Ridley [69]
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. Therefore you would expect that the choice would be most carefully made by the tern and least carefully by the peahen.
Appearances suggest the exact opposite. Peahens survey several males and take 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 up with little fuss. Females are most choosy where least seems to be at stake.22
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, in addition, concrete help from the male. 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 in seduction techniques, called a lek, after the Swedish word for play. Some grouse, several birds of paradise and manakins, plus a number of antelopes, 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 together and parade their wares for visiting females. The characteristic of the lek is that one or a few males, usually those that display near its centre, achieve most of the matings. But the central position of a successful male is not the cause of his success so much as the consequence: other males gather around him.
The best studied of lekking birds is the sage grouse of the American west. It is an extraordinary experience to drive out into the middle of Wyoming before dawn, stop the car on a featureless plain that looks like every other and see it come alive with dancing grouse. Each knows his place; each runs through his routine of inflating the air sacs in his breast and strutting forward, bouncing the fleshy sacs through his feathers for all the world like a dancer at the Folies Bergères. The females wander through this market, and after several days of contemplating the goods on offer they mate with one of the males. That they are choosing, not being forced to choose, seems obvious: the male does not mount the female until she squats in front of him. Minutes later his job is done and her long and lonely parenthood is beginning. She has received only one thing from her mate – genes – and it looks as if she has tried hard to get the best there were to be had.
Yet the problem of greatest choosiness in the species where choice matters least reappears. For a single sage grouse cock may perform half of all the matings at one lek; it is not unknown for this top male to mate thirty or more times in a morning.23 The result is that in the first generation the genetic cream is skimmed from the surface of the population, in the second the cream of the cream, in the third the cream of the cream of the cream, and so on. As any