Placental animals, e.g. might be at each period less variable than Marsupials, and nevertheless have undergone more DIFFERENTIATION and development than marsupials, owing to some advantage, probably brain development.
I am surprised, but do not pretend to form an opinion at Hooker's statement that higher species, genera, etc., are best limited. It seems to me a bold statement.
Looking to the 'Origin,' I see that I state that the productions of the land seem to change quicker than those of the sea (Chapter X., page 339, 3d edition), and I add there is some reason to believe that organisms considered high in the scale change quicker than those that are low. I remember writing these sentences after much deliberation...I remember well feeling much hesitation about putting in even the guarded sentences which I did. My doubts, I remember, related to the rate of change of the Radiata in the Secondary formation, and of the Foraminifera in the oldest Tertiary beds...
Good night, C. DARWIN.
CHARLES DARWIN TO C. LYELL. Down, October 1 [1862].
...I found here (On his return from Bournemouth.) a short and very kind note of Falconer, with some pages of his 'Elephant Memoir,' which will be published, in which he treats admirably on long persistence of type. I thought he was going to make a good and crushing attack on me, but to my great satisfaction, he ends by pointing out a loophole, and adds (Falconer, "On the American Fossil Elephant," in the 'Nat. Hist. Review,' 1863, page 81. The words preceding those cited by my father make the meaning of his quotation clearer. The passage begins as follows: "The inferences which I draw from these facts are not opposed to one of the leading propositions of Darwin's theory. With him," etc. etc.) "with him I have no faith that the mammoth and other extinct elephants made their appearance suddenly...The most rational view seems to be that they are the modified descendants of earlier progenitors, etc." This is capital. There will not be soon one good palaeontologist who believes in immutability. Falconer does not allow for the Proboscidean group being a failing one, and therefore not likely to be giving off new races.
He adds that he does not think Natural Selection suffices. I do not quite see the force of his argument, and he apparently overlooks that I say over and over again that Natural Selection can do nothing without variability, and that variability is subject to the most complex fixed laws...
[In his letters to Sir J.D. Hooker, about the end of this year, are occasional notes on the progress of the 'Variation of Animals and Plants.' Thus on November 24th he wrote: "I hardly know why I am a little sorry, but my present work is leading me to believe rather more in the direct action of physical conditions. I presume I regret it, because it lessens the glory of natural selection, and is so confoundedly doubtful. Perhaps I shall change again when I get all my facts under one point of view, and a pretty hard job this will be."
Again, on December 22nd, "To-day I have begun to think of arranging my concluding chapters on Inheritance, Reversion, Selection, and such things, and am fairly paralyzed how to begin and how to end, and what to do, with my huge piles of materials."]
CHARLES DARWIN TO ASA GRAY. Down, November 6 [1862].
My dear Gray,
When your note of October 4th and 13th (chiefly about Max Muller) arrived, I was nearly at the end of the same book ('Lectures on the Science of Language,' 1st edition 1861.), and had intended recommending you to read it. I quite agree that it is extremely interesting, but the latter part about the FIRST origin of language much the least satisfactory. It is a marvellous problem...[There are] covert sneers at me, which he seems to get the better of towards the close of the book. I cannot quite see how it will forward "my cause," as you call it; but I can see how any one with literary talent (I do not feel up to it) could make great use of the subject in illustration.