sexual selection

[itsyspider]

How does sexual selection reduce fitness?

[wildwood]

Who says it does?

[itsyspider]

My biology teacher said that one of the costs of sexual reproduction is that sexual selection can reduce fitness. I don't really understand that.

[dawkins]

Hi itsyspider,

I think that your teacher was referring to adaptation for the purposes of mating. The most obvious example is the peacock's tail with its fantastic colour and reflective 'eye' patterns not present on a peahen. The plumage of a peacock is designed to attract peahens and nothing more. It does not allow the peacock to run faster or fly better or evade predators; i.e. it has no utility outside the important business of attracting a mate. In fact, there are costs associated with building such a plumage which the female does not pay. The bright plumage is attractive to prey and it takes energy and resources to grow and maintain it. However, although the tail must be expensive to build and maintain it obviously meets the criteria of fitness in terms of producing new peafowl so it is obviously a risk worth taking.

[itsyspider]

Thank you dawkins. But wouldn't that mean that it increases fitness, since the peacock is then able to produce more offspring? My teacher had a list of costs and benefits of sexual and asexual reproduction, and "sexual selection reduces fitness" was on the costs list for sexual reproduction.

[itsyspider]

Sorry, it was "sexual selection can reduce fitness"

[dawkins]

Well, yes I agree but the peahen is doing the choosing and she obviously likes to see a costly display as evidence of good genes so, somewhat ironically, the peacock line has been forced into an elaborate and costly display which has some disadvantages in personal survival, for the opportunity to contribute his genes to future generations. See the handicap principle:

http://en.wikipedia.org/wiki/Handicap_principl e