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.

A genius is a man who has two great ideas.

The symbol and the metaphor are as necessary to science as to poetry.

We have to understand that the world can only be grasped by action, not by contemplation. The hand is more important than the eye ... The hand is the cutting edge of the mind.

Man is not the most majestic of the creatures; long before the mammals even, the dinosaurs were far more splendid. But he has what no other animal possesses: a jigsaw of faculties, which alone, over three thousand million years of life, made him creative. Every animal leaves traces of what he was. Man alone leaves traces of what he created.

The child is not a prisoner of its inheritance; it holds its inheritance as a new creation which its future actions will unfold.

When Da Vinci wanted an effect, he willed, he planned the means to make it happen: that was the purpose of his machines. But the machines of Newton ... are means not for doing but for observing. He saw an effect, and he looked for its cause.