The improver of natural knowledge absolutely refuses to acknowledge authority, as such. For him, skepticism is the highest of duties; blind faith the one unpardonable sin.

The more rapidly truth is spread among mankind the better it will be for them. Only let us be sure that it is the truth.

As a natural process, of the same character as the development of a tree from its seed, or of a fowl from its egg, evolution excludes creation and all other kinds of supernatural intervention.

The facts of variability, of the struggle for existence, of adaptation to conditions, were notorious enough; but none of us had suspected that the road to the heart of the species problem lay through them, until Darwin and Wallace dispelled the darkness.

I really see no harm which can come of giving our children a little knowledge of physiology. ... The instruction must be real, based upon observation, eked out by good explanatory diagrams and models, and conveyed by a teacher whose own knowledge has been acquired by a study of the facts; and not the mere catechismal parrot-work which too often usurps the place of elementary teaching.

The doctrine that all men are, in any sense, or have been, at any time, free and equal, is an utterly baseless fiction.

You may read any quantity of books, and you may almost as ignorant as you were at starting, if you don't have, at the back of yourminds, the change for words in definite images which can only be acquired through the operation of your observing faculties on the phenomena of nature.