I agree with your answer which you give to yourself on this point; and the simile of man now keeping down any new man which might be developed, strikes me as good and new. The white man is "improving off the face of the earth" even races nearly his equals. With respect to islands, I think I would trust to want of time alone, and not to bats and Rodents.
N.B.--I know of no rodents on oceanic islands (except my Galapagos mouse, which MAY have been introduced by man) keeping down the development of other classes. Still MUCH more weight I should attribute to there being now, neither in islands nor elsewhere, [any] known animals of a grade of organisation intermediate between mammals, fish, reptiles, etc., whence a new mammal could be developed. If every vertebrate were destroyed throughout the world, except our NOW WELL-ESTABLISHED reptiles, millions of ages might elapse before reptiles could become highly developed on a scale equal to mammals; and, on the principle of inheritance, they would make some quite NEW CLASS, and not mammals; though POSSIBLY more intellectual! I have not an idea that you will care for this letter, so speculative.
Most truly yours, C. DARWIN.
CHARLES DARWIN TO ASA GRAY. Down, September 26 [1860].
...I have had a letter of fourteen folio pages from Harvey against my book, with some ingenious and new remarks; but it is an extraordinary fact that he does not understand at all what I mean by Natural Selection. I have begged him to read the Dialogue in next 'Silliman,' as you never touch the subject without making it clearer. I look at it as even more extraordinary that you never say a word or use an epithet which does not express fully my meaning. Now Lyell, Hooker, and others, who perfectly understand my book, yet sometimes use expressions to which I demur. Well, your extraordinary labour is over; if there is any fair amount of truth in my view, I am well assured that your great labour has not been thrown away...
I yet hope and almost believe, that the time will come when you will go further, in believing a very large amount of modification of species, than you did at first or do now. Can you tell me whether you believe further or more firmly than you did at first? I should really like to know this. I can perceive in my immense correspondence with Lyell, who objected to much at first, that he has, perhaps unconsciousnessly to himself, converted himself very much during the last six months, and I think this is the case even with Hooker. This fact gives me far more confidence than any other fact.
CHARLES DARWIN TO C. LYELL. 15 Marine Parade, Eastbourne, Friday evening [September 28th, 1860].
...I am very glad to hear about the Germans reading my book. No one will be converted who has not independently begun to doubt about species. Is not Krohn (There are two papers by Aug. Krohn, one on the Cement Glands, and the other on the development of Cirripedes, 'Wiegmann's Archiv,' xxv. and xxvi. My father has remarked that he "blundered dreadfully about the cement glands," 'Autobiography.') a good fellow? I have long meant to write to him. He has been working at Cirripedes, and has detected two or three gigantic blunders,...about which, I thank Heaven, I spoke rather doubtfully. Such difficult dissection that even Huxley failed. It is chiefly the interpretation which I put on parts that is so wrong, and not the parts which I describe. But they were gigantic blunders, and why I say all this is because Krohn, instead of crowing at all, pointed out my errors with the utmost gentleness and pleasantness. I have always meant to write to him and thank him. I suppose Dr. Krohn, Bonn, would reach him.
I cannot see yet how the multiple origin of dog can be properly brought as argument for the multiple origin of man. Is not your feeling a remnant of the deeply impressed one on all our minds, that a species is an entity, something quite distinct from a variety? Is it not that the dog case injures the argument from fertility, so that one main argument that the races of man are varieties and not species--i.e., because they are fertile inter se, is much weakened?
I quite agree with what Hooker says, that whatever variation is possible under culture, is POSSIBLE under nature; not that the same form would ever be accumulated and arrived at by selection for man's pleasure, and by natural selection for the organism's own good.