I prize the conditions under which I have lived because they have permitted me to choose my opportunities, to inquire into such matters as interested me, and to publish what I believed to be true, uncontrolled by any central authority.

Civilization never stands still; if in one country it is falling back, in another it is changing, evolving, becoming more complicated, bringing fresh experience to body and mind, breeding new desires, and exploiting Nature's cupboard for their satisfaction.

No tribe unites with another of its own free will.

Whichever theory we adopt to give a rational explanation of human existence, that theory must take into account and explain the mental nature we see at work in all modern communities.

Tolerance is held to be a condition of mind which is encouraged by, and is necessary for, civilization.

Evolution is unproved and unprovable. We believe it only because the only alternative is special creation, and that is unthinkable.

Man is by nature competitive, combative, ambitious, jealous, envious, and vengeful.