Why Was Sexual Reproduction Selected?

[_Z_]

Dawkins mentions in The Selfish Gene one theory on how gender evolved. Once you have a setup where two partners reproduce by combining their DNA (how this arises, I don't know) by each supplying some material - half an egg, so to speak, it becomes beneficial to "cheat" a bit, supplying a little less than half an egg, so you don't have to waste as many resources creating your "half".

But if a large percentage of the population is cheating so much that they can't reproduce with each other, it'd be benefical to be one of the non-cheaters, since you would be one of the few who can reproduce with anybody. It's concievable that this mechanism could run-away and make some of the population sperm producers and some egg producers.

Incidently, many differences between males and females stem from the fact that females produce more of the reproductive material than males do. It would be bizarre, for instance, if the gender who produces less of the material was the one who tended to be in charge of a child before hatching/birth.

Z

[Rduke55]

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females produce more of the reproductive material than males do

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Great point. Things like parental investment is huge in determining a ton of stuff, including the operational sex ratio that underlies so much of sexual selection.

Not only differences in the gametes (which is smaller in most mammals compared to other critters) but mammalian females also get stuck gestating the offspring. Then you got lactation, etc.

[Borodog]

Not that that isn't all interesting stuff, but it all comes about after sex has already been established.