The beauty of a living thing is not the atoms that go into it, but the way those atoms are put together.

The suppression of uncomfortable ideas may be common in religion or in politics, but it is not the path to knowledge, and there's no place for it in the endeavor of science. We do not know beforehand where fundamental insights will arise from about our mysterious and lovely solar system. The history of our study of our solar system shows us clearly that accepted and conventional ideas are often wrong, and that fundamental insights can arise from the most unexpected sources.

Modern Darwinism makes it abundantly clear that many less ruthless traits, some not always admired by robber barons and Fuhrers - altruism, general intelligence, compassion - may be the key to survival.

The fact that someone says something doesn't mean it's true. Doesn't mean they're lying, but it doesn't mean it's true.

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.

Because men, compared to male chimps, have such relatively small testicles (large testicles indicate a species where many males mate, one after the other, with the same female), we might guess that promiscuous societies were uncommon in the immediate human past.

All civilizations become either spacefaring or extinct.