I always make special notes about evidence that contridicts me: supportive evidence I can remember without trying.

It is always advisable to perceive clearly our ignorance.

It strikes me that all our knowledge about the structure of our Earth is very much like what an old hen would know of the hundred-acre field in a corner of which she is scratching.

Nothing is easier than to admit in words the truth of the universal struggle for life, or more difficult--at least I have found it so--than constantly to bear this conclusion in mind.

I am not apt to follow blindly the lead of other men

The survival or preservation of certain favoured words in the struggle for existence is natural selection.

... probably all the organic beings which have ever lived on this earth have descended from some one primordial form, into which life was first breathed.