What does ethics have to do with it? People reproduce because they are programmed by evolution to reproduce. Period. It's as simple as that. The only thing all of our ancestors had in common, all the way back to the most primitive anaerobic molecular protolife, is that they all survived at least long enough to breed. That's the only reason we do it. Those of our ancestors who didn't feel that strongly about it probably didn't survive long enough to have offspring.

You might argue successfully that the survivors are, by definition, very well adapted to their environment, but so what? The environment changes randomly, all you've proven is that the last generation is exquistely adapted to last long enough to breed. Nothing else. There is no purpose to evolution. It is a completely stochastic phenomenon.

If you start of with a bazillion coins and flip them, tossing out each one that comes up "tails", and you keep flipping and tossing out tails until only one is left, there is nothing special about that last coin, even though it has come up heads every single time it was tossed. It still has only a 50-50 chance of coming up heads again.

The vast majority of organisms on this planet reproduce without even realizing they are doing so, only a tiny minority are even aware of their offspring, much less consciously modify their own behavior in order to provide their young with an environment that will give them a better chance to also reproduce. And even that propensity to sacrifice is competitively bred into them by evolution. To think we are fundamentally any different is the height of arrogance.

We fight and sacrifice for posterity, whether it be genetic or cultural, because we choose to do so. It is a purely conscious act. If that has any value, it is value we define and create for ourselves. It is an existential decision we make. We may be programmed by evolution to love our children, but before you feel too smug about our supposed moral superiority over the beasts, recall that we don't often share the same zeal for protecting others' offspring, especially when we have to choose between ours and someone else's. The lioness may fight to the death to protect her cubs, but the alpha male of the pride will eat those who are not his own offspring. He has an obligation to his DNA he does not owe to that of his rivals. Wolf packs don't work the same way, only one male and female breed but all in the pack will fight to defend their cubs. Are wolves more moral or ethical than lions, or did evolution simply find another behavior pattern to be more efficient in their case?

We are highly complex creatures, and we are social animals. Our culture modifies our biological behavior, too. But deep down, those same stochastic rules are operating, if not at the molecular level, then in the cultural dimension. and if not there, then in the psychological sphere.

I chose when very young to not have children. I did so for purely selfish reasons. I just wasn't born with that desire, and I couldn't be coerced or intimidated into adopting it. So unless I've unknowingly bred some little ER out there, my selfishness will be bred out of the race. That seems fair enough to me.