In the future I see open fields for more important researches. Psychology will be securely based on the foundation already laid by Mr. Herbert Spencer, that of the necessary acquirement of each mental power and capacity by graduation.

Your printers have made but one blunder,Correct it instanter, and then for the thunder!We'll see in a jiffy if this Mr S[pencer]Has the ghost of a claim to be thought a good fencer.To my vision his merits have still seemed to dwindle,Since I have found him allied with the great Dr T[yndall]While I have, for my part, grown cockier and cockier,Since I found an ally in yourself, Mr L[ockyer]And am always, in consequence, thoroughly willin',To perform in the pages of Nature's M[acmillan].

Adam is fading out. It is on account of Darwin and that crowd. I can see that he is not going to last much longer. There's a plenty of signs. He is getting belittled to a germ—a little bit of a speck that you can't see without a microscope powerful enough to raise a gnat to the size of a church.('The Refuge of the Derelicts' collected in Mark Twain and John Sutton Tuckey, The Devil's Race-Track: Mark Twain's Great Dark Writings (1980), 340-41. - 1980)

The expression often used by Mr. Herbert Spencer of the Survival of the Fittest is more accurate, and is sometimes equally convenient.

I fully agree with all that you say on the advantages of H. Spencer's excellent expression of 'the survival of the fittest.' This, however, had not occurred to me till reading your letter. It is, however, a great objection to this term that it cannot be used as a substantive governing a verb; and that this is a real objection I infer from H. Spencer continually using the words, natural selection.(Letter to A. R. Wallace July 1866)