As agonizing a disease as cancer is, I do not think it can be said that our civilization is threatened by it. ... But a very plausible case can be made that our civilization is fundamentally threatened by the lack of adequate fertility control. Exponential increases of population will dominate any arithmetic increases, even those brought about by heroic technological initiatives, in the availability of food and resources, as Malthus long ago realized.

The difference between physics and metaphysics is not that the practitioners of one are smarter than the practitioners of the other. The difference is that the metaphysicist has no laboratory.

The beauty of a living thing is not the atoms that go into it, but the way those atoms are put together. Information distilled over 4 billion years of biological evolution. Incidentally, all the organisms on the Earth are made essentially of that stuff. An eyedropper full of that liquid could be used to make a caterpillar or a petunia if only we knew how to put the components together.

I set before you two ways: You can use your technology to destroy yourselves or to carry you to the planets and the stars. It's up to you.

It goes with a courageous intent to greet the universe as it really is, not to foist our emotional predispositions on it but to courageously accept what our explorations tell us.

We invest far off places with a certain romance... Long summers, mild winters, rich harvests, plentiful game; none of them lasts for ever. Your own life, or your bands, or even your species - might be owed to a restless few, drawn by a craving they can hardly articulate or understand, to undiscovered lands, and new worlds.

I believe that the extraordinary should be pursued. But extraordinary claims require extraordinary evidence.