Without wilderness, the world's a cage.

I don't think we have very good records about what they were thinking except, as I pointed out earlier today, that they did invent our political system.

Yet another proposal would have us rocket the waste into the sun, but, as you're probably aware, about one in ten of our space shots doesn't quite make it out of the earth's gravitational field.

For how many people do you think might yet stand on this planet before the sun grows cold? That's the responsibility we hold in our hands.

Bring diversity back to agriculture. That's what made it work in the first place.

Overpopulation is perhaps the biggest problem facing us, and immigration is part of that problem. It has to be addressed.

Perhaps we'll realize that each of us has not one vote but ten thousand or a million.