WEIT Chap6

First of all, sex is good.

HOW SEX DRIVES EVOLUTION

First of all... sex is good... Pierre.brawand 19 avril 2011 à 22:36 (CEST)

Why sex?

that's THE key question... and the answer is not so simple... [ [Utilisateur:Pierre.brawand|Pierre.brawand]] 19 avril 2011 à 22:39 (CEST)

If sex between males and females didn't exist and the females could clone themselves by asexual reproduction, males would disappeared completely and the evolution of species would ended with them. Sex exists to allow animals to survive by adapting them to the environment that is constantly changing. The most important element is that sexual reproduction, by the random combination of genes, produces variability and thanks to this variability, some individuals are better adapted to the environment than others.

Why two sexes?

Jerry A.Coyne doesn't give any biological explanations for this question. In fact, he just says that "the question of the number of sexes is a messy theoretical issue". We can't really imagine more sexes because evolution made our sexes "compatible" to reproduce together. The differences between the males and the females gametes are also due to evolution. Furthermore, we can just imagine if there were three sexes or more... Today, with two sexes there are a lot of difficulties to find the good partner to reproduce. More sexes would be harder, would take more time, and evolution would be completely unsettled.

What is sexual selection?

Sexual selection is a natural process that occurs in animals just before mating: it's a selection that increases an individual's chance of getting a mate. There are two forms:

1) Male-male competition (The Law of Battle): It's a struggle between the males for the possession of females. Two males of the same species fight out, and the goal is to drive off the other male in order to win access to females. This kind of selection produces (allows the developpment of) armaments, like stronger weapons, larger body size or anything that helps a male win physical contests.

2) Female choice: This is a choice made by females. They "compare" males to each others and recognize the ones which have the most impressive physical features; for example, females birds prefer males with big tails, bright colors etc. And females frogs prefer males with complex calls. In those cases, the "armaments" that males deploy are different.

What is sexual dimorphism?

Sexual dimorphisms are traits that differ between males and females of a species. (ex: tails, colors, songs, etc). Through years, biologists have found that sexually dimorphic traits in males, even if they are developped in order to seduce females (bright colors, long tails, etc), show negatives aspects: during the seduction phase, males don't pay enough attention to predators (they are more vulnerable!) and they are more susceptible to be attacked by predators than females because of their bright features. (These features are nearly always restricted to males).

Why choose ? And why is it the role of females?

AudreyM 26 mai 2011 à 11:22 (CEST)

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