MsMary wrote:I don't get it.
Suppose two populations. One that reproduces sexually, one that reproduces asexual through budding or another form of cloning.
The assexual population will rapidly be able to outreproduce the sexual population, since every member in the assexual population can bear young, yet only 1/2 (more or less, depending on species) of the sexual population can bear young (the females.)
Males carry a high ecological cost: They require food and living space, just as females do, and yet they contribute very little to the reproductive process in most species (and do not have to contribute more than a few minutes of time in humans, either.) It makes more sense from a reproductive standpoint to have an asexual population that reproduces via some form of budding or aparthenogenesis, to maximise reproductive potential.
However, sexual populations have two advantages over asexual populations which are of high importance.
Firstly, in a sexual population, the odds of two seperate mutations, which interact together in some beneficial manner, coming together after having arisen seperately, is infinitely greater than in an asexual population. If asexual lineage A and asexual lineage B develop, respectively, mutation A and mutation B, then each one will have to develop the other mutation on its own, since in the asexual population, there is no gene-mixing between lineages.
Secondly, in a sexual population, having a kind mixes around your genes for compatability types, and for surface markers on cells that play a role in immunodefense. A disease that killed your parents is less likely to kill you -- which is why the Spanish Flu was so devestating so suddenly, and then disappeared. In a sexual population, parasites, such as viruses, bacteria, and other parasites, must evolve along side the host population, because the host population's defenses are constantly changing around a certain equilibrium of occurance of various genes. In an asexual population, once the parasites evolve a particular genotype that is effective, it will be effective for a great deal of time, because incidence of mutation is much less in asexual beings.
In short: Males. We're what keeps us healthy sometimes.