Evolution advances, not by a priori design, but by the selection of what works best out of whatever choices offer. We are the products of editing, rather than of authorship.

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

Four elements, Hydrogen, carbon, oxygen and nitrogen, also provide an example of the astonishing togetherness of our universe. They make up the "organic" molecules that constitute living organisms on a planet, and the nuclei of these same elements interact to generate the light of its star. Then the organisms on the planet come to depend wholly on that starlight, as they must if life is to persist. So it is that all life on the Earth runs on sunlight. [Referring to photosynthesis]

A lecture is much more of a dialogue than many of you probably realize.

I think all of you know there is no adequate defense against massive nuclear attack.

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

Every creature alive on the earth today represents an unbroken line of life that stretches back to the first primitive organism to appear on this planet; and that is about three billion years.