The world can only be grasped by action, not by contemplation.

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.

Da Vinci was as great a mechanic and inventor as were Newton and his friends. Yet a glance at his notebooks shows us that what fascinated him about nature was its variety, its infinite adaptability, the fitness and the individuality of all its parts. By contrast what made astronomy a pleasure to Newton was its unity, its singleness, its model of a nature in which the diversified parts were mere disguises for the same blank atoms.

Science, like art, is not a copy of nature but a re-creation of her.

It's a sort of curious phenomenon that God is somehow not quite as nice as the devil; the devil doesn't punish you for behaving well, but God punishes you for behaving badly.

Dissent is the mark of freedom.

Dissent is the native activity of the scientist, and it has got him into a good deal of trouble in the last years. But if that is cut off, what is left will not be a scientist. And I doubt whether it will be a man.