Imagine, just for a minute, that we are the only planet in the observable universe ever to have developed intelligent life. What a huge responsibility that is! If we, as life forms, are unique in all of creation, then we owe it to somebody to keep it up and running. Our sun has about five billion years left in her. The geological record indicates the Earth's biosphere undergoes an extinction-level event every so many million years. Call it 500 million. If the human race snuffs it, Earth has maybe 10 more chances to evolve a decent life form with enough sense not to keep all its gametes in one basket. And there's no guarantee anything even as good as us will ever come around again.

If we are alone, then the universe is our sandbox. We can claim the whole ten-to-the-fifteenth-power light-years' diameter of spacetime as our domain. We can cross the galaxy in a few million years easy, and hopefully have folks out in some far-flung galaxy by the time we collide with Andromeda and the cinders of our solar system are ripped bodily from one another. Best of all, there would always be someplace else to go. Even if we went every direction at once as fast as we could, I don't think we'd reach the edge of existence before heat death set in.

Everyone reading this has, presumably, one thing in common. You are alive. Which is true because your parents were alive long enough to produce you, because their parents yadda yadda ad infinitum. We are the end result of uncounted generations of organisms whose only qualification for membership in the gene pool was that they stayed alive long enough to have sex. Our ancestors weren't the best, the brightest, the strongest, the fastest. They were the survivors. Possibly the ones with the coolest cars, but that's beside the point.

We have evolved from tough little knots of flesh that didn't know when to pack it in. Whatever else we do and however we do it, the thing we do best is make more of us. If the planet goes kaput tomorrow, the universe loses a potentially unique phenomenon in its fundament, and we lose the game we've been playing since Mr. and Mrs. Amino Acid started shacking up. We owe it to ourselves as the last in a long line of ornery bastards not to let that happen.