When you have no experience of pain, it is rather hard to experience joy.

The Vietnamese have a secret weapon. It's their willingness to die beyond our willingness to kill. In effect, they've been saying, You can kill us, but you'll have to kill a lot of us; you may have to kill all of us. And, thank heaven, we are not yet ready to do that.

About two million years ago, man appeared. He has become the dominant species on the earth. All other living things, animal and plant, live by his sufferance. He is the custodian of life on earth, and in the solar system. It's a big responsibility.

We have fallen in love with the body. That's that thing that looks back at us from the mirror. That's the repository of that lovely identity that you keep chasing all your life.

I think I know what is bothering the students. I think that what we are up against is a generation that is by no means sure that it has a future.

I have lived much of my life among molecules. They are good company.

[Attributing the origin of life to spontaneous generation.] However improbable we regard this event, it will almost certainly happen at least once.... The time... is of the order of two billion years.... Given so much time, the "impossible" becomes possible, the possible probable, and the probable virtually certain. One only has to wait: time itself performs the miracles.