The most powerful drive in the ascent of man is his pleasure in his own skill. He loves to do what he does well. And having done it well, he loves to do it better.

The preoccupation with the choice of a mate both by male and female I regard as a continuing echo of the major selective force by which we have evolved.

Ask an impertinent question and you are on the way to the pertinent answer.

To me, being an intellectual doesn't mean knowing about intellectual issues; it means taking pleasure in them.

Revolutions are not made by fate but by men.

The progress of science is the discovery at each step of a new order which gives unity to what had seemed unlike.

The values by which we are to survive are not rules for just and unjust conduct, but are those deeper illuminations in whose light justice and injustice, good and evil, means and ends are seen in fearful sharpness of outline.