No amount of experimentation can ever prove me right; a single experiment can prove me wrong.

The great variability of all the external differences between the races of man, likewise indicates that they cannot be of much importance; for if important, they would long ago have been either fixed and preserved, or eliminated.

Great is the power of steady misrepresentation.

Whatever the mind of man creates, should be controlled by man's character.

Man in his arrogance thinks himself a great work, worthy of the interposition of a deity. More humble, and I believe truer, to consider him created from animals.

You can judge a man's true character by the way he treats his fellow animals.