Our challenge is to give what account we can of what becomes of life in the solar system, this corner of the universe that is our home; and, most of all, what becomes of men-all men, of all nations, colors, and creeds. This has become one world, a world for all men. It is only such a world that can now offer us life, and the chance to go on.

I do not want to believe in God. Therefore I choose to believe in that which I know is scientifically impossible, spontaneous generation leading to evolution.

I am growing old, and my future, so to speak, is already behind me.

Civilization will end within 15 or 30 years unless immediate action is taken against problems facing mankind.

If the germ plasm wants to swim in the ocean, it makes itself a fish; if the germ plasm wants to fly in the air, it makes itself a bird. If it wants to go to Harvard, it makes itself a man. The strangest thing of all is that the germ plasm that we carry around within us has done all those things. There was a time, hundreds of millions of years ago, when it was making fish. Then ... amphibia ... reptiles ... mammals, and now it's making men.

I tell my students to try early in life to find an unattainable objective.

We are living in a world in which all wars are wars of defense.