A Tale of Picky Women

BBC News - Do you think I'm sexy? Why peacock tails are attractive



One of the most spectacular displays in the bird world. It shows the power of 'selfish' genes and how they have no regard for the individuals whose bodies they are using to get themselves through time, one generation at a time.



The peacock's tails is a product of female sex selection and comes from the differential investment male and female organisms make to ensuring their respective reproductive cells, their gametes, produce a new carrier of their genes. Females produce a small number of sedentary games, or egg cells while males produce a large number of motile gamete. In the vertebrates these are called sperm cells. Males can therefore afford to be relatively liberal and carefree with their sperm provided at least one finds a 'female' gamete, but the female needs to guard every one of hers.



This means that a female needs to pick and choose her mate because a poor choice could result in a wasted egg. Males, on the other hand, only waste a single ejaculation if they make a poor choice.



So how did this translate into peacock's tails?



Well, with picky females, males have to compete with other males for her attention and her favour, which puts her in charge. So, anything which makes the male more noticeable or more attractive becomes bound up with the evolutionary process by being strongly favoured. Female sex selection thus becomes a powerful form of natural selection; a particularly demanding and unforgiving natural selection sieve only allowing through those genes which are allied to those which the females will choose.

I can see no good reason to doubt that female birds, by selecting, during thousands of generations, the most melodious or beautiful males, according to their standard of beauty, might produce a marked effect.



I strongly suspect that some well-known laws with respect to the plumage of male and female birds, in comparison with the plumage of the young, can be explained on the view of plumage having been chiefly modified by sexual selection,

Charles Darwin, On the Origin of Species by Means of Natural Selection, 1859

As the above research showed, the peacock has to work hard to keep the attention of the peahen because she is easily distracted by other things in her environment - which itself has evolved because she is a prey species for several predators so can't afford to be distracted for too long. The peacock is having to compete not just with other males but potentially with tigers and other predators and even with the wind rustling leaves and bushes. He has also had to overcome dense vegetation, so, although the peacock having gained her attention, the peahen only bothers to take notice of the lower parts of his display, he needs a long tail to get her attention in the first place because their environment has dense vegetation in it. The environment tells the peacock genes, grow a long peacock tail - or don't reproduce.



The result of this is that the males have been driven down an evolutionary path by female sex selection which has resulted in him being disposable. His long tail makes flight difficult and his bright colour and elaborate display seems to be practically designed to attract tigers and other predators. The female can always find another eager male with which to fertilise her few precious eggs. Female sex selection, for peacocks, has obviously out-competed the other natural selection factors which would be expected to produce birds which can hide from predators and easily escape from them.



No intelligent, compassionate designer would design males so they need adopt a practically suicidal strategy in order to reproduce. Selfish genes, on the other hand, have no compassion and no plan. They do exactly what the environment selects them to do and the only measure of effectiveness is that they reproduce themselves and survive into the next generation. That's what they built their carriers for.



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