Mr.Huxley quotes a letter from Darwin to Zacharias, "But I did not become convinced that species were mutable until, I think, two or three years [after 1837] had elapsed" (see Letter 278).

This passage, which it must be remembered was written in 1877, is all but irreconcilable with the direct evidence of the 1837 note-book.

A series of passages are quoted from it in the "Life and Letters," Volume II., pages 5 et seq., and these it is impossible to read without feeling that he was convinced of immutability.

He had not yet attained to a clear idea of Natural Selection, and therefore his views may not have had, even to himself, the irresistible convincing power they afterwards gained; but that he was, in the ordinary sense of the word, convinced of the truth of the doctrine of evolution we cannot doubt.

He thought it "almost useless" to try to prove the truth of evolution until the cause of change was discovered.