Women After All: Sex, Evolution, and the End of Male Supremacy by Melvin Konner Page B
Authors: Melvin Konner
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got grander and gaudier because they caught peahens’ eyes and the hens said, You or, at least, Oh, as well him as another . The rest is evolutionary history, the grandest display of male fashion ever to sidle and glide across an earthen runway, as if he’s thinking, Don’t pass me by, girl, it doesn’t get better than this , while she’s thinking, Boy, get over yourself. She may play hard to get or wait for an even spiffier male. Actually, in time she may choose several mates. But maybe in the end this one’s not so bad, and after all, she is in the mood.
As for just how good a mood she is in, we know, thanks to beautifully designed experiments by Marion Petrie and her colleagues over many years, that peahens lay more eggs for males with larger trains (possibly a product of their hormonal state) and that their offspring grow and survive better after release into the wild even when the hens are randomly assigned to different males and the offspring are reared under matching conditions. The suggestion is that a large train is an honest advertisement of overall quality, then imparted to offspring, but it could also be that the most impressive males (who don’t do any of the child care themselves) inspire hens to invest more in the young.
The peahen’s preference has turned out to be more complex than it seemed at first, but an elegant 2013 study by Roslyn Dakin and Robert Montgomerie proved decisively that one component ofthe display matters to her a lot: “Our study shows that the blue-green eyespot color overwhelmingly influences peacock mating success.” It’s when those spots catch the sun at a certain angle that the hens are won over. The authors, who titled their paper “Eye for an Eyespot,” are continuing to examine other aspects of this stunning romantic dance—and for the most part confirming Darwin’s original surmise.
We’ve seen something like this process in jacanas, except in peacocks it’s the males who compete for the precious parental capacity owned by females. Peacock males contribute nothing to the care of the young. They put their energy into building beautiful tails and fanning them out in females’ view. According to zoologist Amotz Zahavi’s “handicap principle,” such useless or even detrimental appendages—peacock feathers puzzled Darwin mightily, because they seemed such a lure for predators—actually signal quality, because only a superior male could afford the cost and risk. Many studies have now shown that these add-ons do indeed signal male quality by other standards—measures of health, such as parasite load. In this case, the ornament and the antics that go with it are dubbed “honest advertisements” of excellence.
But according to mathematical biologist Ronald Fisher’s classic theory of “runaway selection” (also known as the “sexy sons” hypothesis), it may not really matter, because once the preference for prettier tails gets started (even by chance), females will keep choosing them because their sons will be better off having them, and this cycle will strengthen generation by generation. This should be most true in rich environments, where the cost of frills can be more easily borne and the gain for chosen males great. Whether the adornments evolved by handicap or runaway selection, they work; in most experiments, peahens prefer the cocks with more elaborate tails.
Similar effects have been shown in many species, including ones that to us look much less fine than peacocks. Although coloration also matters, tail length in male barn swallows can be manipulatedto influence mating success; under otherwise natural conditions, females mated to males who’d first had their tails lengthened are better at brooding eggs and steal fewer copulations with other males. This is why long tails have persisted despite their possible disadvantage in foraging and survival.
In palmate newts, the male’s tail ends in a threadlike filament. In their wild little world of
As for just how good a mood she is in, we know, thanks to beautifully designed experiments by Marion Petrie and her colleagues over many years, that peahens lay more eggs for males with larger trains (possibly a product of their hormonal state) and that their offspring grow and survive better after release into the wild even when the hens are randomly assigned to different males and the offspring are reared under matching conditions. The suggestion is that a large train is an honest advertisement of overall quality, then imparted to offspring, but it could also be that the most impressive males (who don’t do any of the child care themselves) inspire hens to invest more in the young.
The peahen’s preference has turned out to be more complex than it seemed at first, but an elegant 2013 study by Roslyn Dakin and Robert Montgomerie proved decisively that one component ofthe display matters to her a lot: “Our study shows that the blue-green eyespot color overwhelmingly influences peacock mating success.” It’s when those spots catch the sun at a certain angle that the hens are won over. The authors, who titled their paper “Eye for an Eyespot,” are continuing to examine other aspects of this stunning romantic dance—and for the most part confirming Darwin’s original surmise.
We’ve seen something like this process in jacanas, except in peacocks it’s the males who compete for the precious parental capacity owned by females. Peacock males contribute nothing to the care of the young. They put their energy into building beautiful tails and fanning them out in females’ view. According to zoologist Amotz Zahavi’s “handicap principle,” such useless or even detrimental appendages—peacock feathers puzzled Darwin mightily, because they seemed such a lure for predators—actually signal quality, because only a superior male could afford the cost and risk. Many studies have now shown that these add-ons do indeed signal male quality by other standards—measures of health, such as parasite load. In this case, the ornament and the antics that go with it are dubbed “honest advertisements” of excellence.
But according to mathematical biologist Ronald Fisher’s classic theory of “runaway selection” (also known as the “sexy sons” hypothesis), it may not really matter, because once the preference for prettier tails gets started (even by chance), females will keep choosing them because their sons will be better off having them, and this cycle will strengthen generation by generation. This should be most true in rich environments, where the cost of frills can be more easily borne and the gain for chosen males great. Whether the adornments evolved by handicap or runaway selection, they work; in most experiments, peahens prefer the cocks with more elaborate tails.
Similar effects have been shown in many species, including ones that to us look much less fine than peacocks. Although coloration also matters, tail length in male barn swallows can be manipulatedto influence mating success; under otherwise natural conditions, females mated to males who’d first had their tails lengthened are better at brooding eggs and steal fewer copulations with other males. This is why long tails have persisted despite their possible disadvantage in foraging and survival.
In palmate newts, the male’s tail ends in a threadlike filament. In their wild little world of
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