Originally Posted by
Neichus
Well, I'm trying to make a specific point. There is a tendency for people to attribute survival of a [i]species[/i] to being the evolutionary pressure. I was simply underlining that survival of the species as a whole is a byproduct of selection on individuals.
For instance, males are largely useless for most species that are not monogamous. There are far far more males than necessary, because one male is capable of fertilizing hundreds of females. The flip side is that most males do not do so, and in most species only a small percentage of the males reproduce. So males are like buying a lottery ticket: most of the time you lose, but sometimes you win big. Females are a nice, safe investment because for most species if they reach reproductive age they will pay off (fitness-wise).
Now, if there were pressure at the species level you would expect that we'd get like a 10:1 ratio of females:males in these species since that would be better suited to the level of investment of each. Instead you get a 1:1 even in species that are highly polygynous because the higher the female:male ratio becomes the better males are as an investment (it's like a harem anime; if it's only one guy in a land of girls, he's got a pretty good chance). So selective pressure drags the sex ratio back to about even, which is a detriment to the species as a whole since it's a lot of wasted bodies that are consuming resources, fighting each other, and generally being a pain.