You could not even remain idle, as I have done, for three weeks! What you say about Lyell pleases me exceedingly; I had not at all inferred from his letters that he had come so much round. I remember thinking, above a year ago, that if ever I lived to see Lyell, yourself, and Huxley come round, partly by my book, and partly by their own reflections, I should feel that the subject is safe, and all the world might rail, but that ultimately the theory of Natural Selection (though, no doubt, imperfect in its present condition, and embracing many errors) would prevail. Nothing will ever convince me that three such men, with so much diversified knowledge, and so well accustomed to search for truth, could err greatly. I have spoken of you here as a convert made by me; but I know well how much larger the share has been of your own self-thought. I am intensely curious to hear Huxley's opinion of my book. I fear my long discussion on Classification will disgust him; for it is much opposed to what he once said to me.
But, how I am running on. You see how idle I am; but I have so enjoyed your letter that you must forgive me. With respect to migration during the glacial period: I think Lyell quite comprehends, for he has given me a supporting fact. But, perhaps, he unconsciously hates (do not say so to him) the view as slightly staggering him on his favourite theory of all changes of climate being due to changes in the relative position of land and water.
I will send copies of my book to all the men specified by you;...you would be so kind as to add title, as Doctor, or Professor, or Monsieur, or Von, and initials (when wanted), and addresses to the names on the enclosed list, and let me have it pretty SOON, as towards the close of this week Murray says the copies to go abroad will be ready. I am anxious to get my view generally known, and not, I hope and think, for mere personal conceit...
CHARLES DARWIN TO C. LYELL. Ilkley, Yorkshire, October 25th [1859].
...Our difference on "principle of improvement" and "power of adaptation" is too profound for discussion by letter. If I am wrong, I am quite blind to my error. If I am right, our difference will be got over only by your re-reading carefully and reflecting on my first four chapters. I supplicate you to read these again carefully. The so-called improvement of our Shorthorn cattle, pigeons, etc., does not presuppose or require any aboriginal "power of adaptation," or "principle of improvement;" it requires only diversified variability, and man to select or take advantage of those modifications which are useful to him; so under nature any slight modification which CHANCES to arise, and is useful to any creature, is selected or preserved in the struggle for life; any modification which is injurious is destroyed or rejected; any which is neither useful nor injurious will be left a fluctuating element. When you contrast natural selection and "improvement," you seem always to overlook (for I do not see how you can deny) that every step in the natural selection of each species implies improvement in that species in relation to its conditions of life. No modification can be selected without it be an improvement or advantage. Improvement implies, I suppose, each form obtaining many parts or organs, all excellently adapted for their functions. As each species is improved, and as the number of forms will have increased, if we look to the whole course of time, the organic condition of life for other forms will become more complex, and there will be a necessity for other forms to become improved, or they will be exterminated; and I can see no limit to this process of improvement, without the intervention of any other and direct principle of improvement. All this seems to me quite compatible with certain forms fitted for simple conditions, remaining unaltered, or being degraded.
If I have a second edition, I will reiterate "Natural Selection," and, as a general consequence, "Natural Improvement."
As you go, as far as you do, I begin strongly to think, judging from myself, that you will go much further.