To Charles Lyell 20 October 
Wells Terrace | Ilkley Otley | Yorkshire
My dear Lyell
I have been reading over all your letters consecutively; & I do not feel that I have thanked you half enough, for the extreme pleasure which they have given me & for their utility.—
I see in them evidence of fluctuation in the degree of credence you give to the theory; nor am I at all surprised at this, for many & many fluctuations I have undergone.
There is one point in your letter, which I did not notice, about the animals (& many plants) naturalised in Australia, which you think could not endure without man’s aid.1 I cannot see how man does aid the feral cattle. But letting that pass, you seem to think that because they suffer prodigious destruction during droughts, that they would all be destroyed. In the “gran secos” of La Plata the indigenous animals, such as the American deer, die by thousands & suffer apparently as much as the cattle. In parts of India, after a drought it takes 10 or more years before the indigenous mammals get up to their full number again. Your argument would, I think, apply to the aborigines as well as to the feral. An animal or plant which becomes feral in one small territory might be destroyed by climate but I can hardly believe when once feral over several large territories. Again I feel inclined to swear at climate!—2
Do not think me very impudent for attacking you about climate; you say you doubt whether man could have existed under Eocene climate; but man can now withstand the climate of Esquimaux-land & West Equatorial Africa; & surely you do not think Eocene climate differed from present, througout all Europe, as much as the Arctic regions differ from Equatorial Africa.—
With respect to organisms being created on American type in America, it might, I think, be said, that they were so created to prevent them being too well created so as to beat the aborigines; but this seems to me somehow a monstrous doctrine.—
I have reflected a good deal on what you say on necessity of continued intervention of creative power.3 I cannot see this necessity; & its admission, I think would make theory of nat. select. valueless. Grant a simple archetypal creature, like the Mud-fish or Lepidosiren, with the five senses & some vestige of mind, & I believe Natural Selection will account for production of every Vertebrate animal.
Farewell,—forgive me for indulging in this prose—& believe me with cordial thanks | Your ever attached disciple | Charles Darwin
When, & if, you reread, I supplicate you to write on margin, word “expand”, when too condensed or “not clear” or “[reverse question mark].”—such marks would cost you little trouble, & I could copy them, & reflect on them, & their value would be infinite to me.—
My larger book will have to be wholly rewritten, & not merely present volume expanded;4 so that I want to waste as little time over this volume as possible, if another Edition be called for; but I fear subject will be too perplexing, as I have treated it, for general public.—
Comments on CL’s letters.
Discusses foreign animals naturalised in Australia and elsewhere.
Affirms man’s capacity to survive in Eocene climate.
Comments on American types.
Denies necessity for "continued intervention of creative power".
Please cite as
Darwin Correspondence Project, “Letter no. 2507,” accessed on 9 December 2016, http://www.darwinproject.ac.uk/DCP-LETT-2507