Scientists are people of very dissimilar temperaments doing different things in very different ways. Among scientists are collectors, classifiers and compulsive tidiers-up; many are detectives by temperament and many are explorers; some are artists and others artisans. There are poet-scientists and philosopher-scientists and even a few mystics.

When asked to make the formal declaration that I did not intend to overthrow the Constitution of the United States, I was fool enough to reply that I had no such purpose, but that were I to do it by mistake I should be inexpressibly contrite.

Heredity proposes and development disposes.

Scientists who think science consists of unprejudiced data-gathering without speculation are merely cows grazing on the pasture of knowledge.

A scientist is no more a collector and classifier of facts than a historian is a man who complies and classifies a chronology of the dates of great battles and major discoveries.

We cannot point to a single definitive solution of any one of the problems that confront us — political, economic, social or moral, that is, having to do with the conduct of life. We are still beginners, and for that reason may hope to improve. To deride the hope of progress is the ultimate fatuity, the last word in poverty of spirit and meanness of mind. There is no need to be dismayed by the fact that we cannot yet envisage a definitive solution of our problems, a resting-place beyond which we need not try to go.

It is ... a sign of the times-though our brothers of physics and chemistry may smile to hear me say so-that biology is now a science in which theories can be devised: theories which lead to predictions and predictions which sometimes turn out to be correct. These facts confirm me in a belief I hold most passionately-that biology is the heir of all the sciences.