I hope that you will allow me to express my gratitude for the pleasure and instruction which I have derived from reading it. It seems to me to be an admirable work; and is by far the best case which I have ever met with, showing the direct influence of the conditions of life on the organization.
Mr. Hyatt, who has been studying the Hilgendorf case, writes to me with respect to the conclusions at which he has arrived, and these are nearly the same as yours. He insists that closely similar forms may be derived from distinct lines of descent; and this is what I formerly called analogical variation. There can now be no doubt that species may become greatly modified through the direct action of the environment. I have some excuse for not having formerly insisted more strongly on this head in my 'Origin of Species,' as most of the best facts have been observed since its publication.
With my renewed thanks for your most interesting essay, and with the highest respect, I remain, dear Sir,
Yours very faithfully, CHARLES DARWIN.
CHARLES DARWIN TO E.S. MORSE. Down, April 23, 1877.
My dear Sir,
You must allow me just to tell you how very much I have been interested with the excellent Address ("What American Zoologists have done for Evolution," an Address to the American Association for the Advancement of Science, August, 1876. Volume xxv. of the Proceedings of the Association.) which you have been so kind as to send me, and which I had much wished to read. I believe that I had read all, or very nearly all, the papers by your countrymen to which you refer, but I have been fairly astonished at their number and importance when seeing them thus put together. I quite agree about the high value of Mr. Allen's works (Mr. J.A. Allen shows the existence of geographical races of birds and mammals. Proc. Boston Soc. Nat. Hist. volume xv.), as showing how much change may be expected apparently through the direct action of the conditions of life. As for the fossil remains in the West, no words will express how wonderful they are. There is one point which I regret that you did not make clear in your Address, namely what is the meaning and importance of Professors Cope and Hyatt's views on acceleration and retardation. I have endeavoured, and given up in despair, the attempt to grasp their meaning.
Permit me to thank you cordially for the kind feeling shown towards me through your Address, and I remain, my dear Sir,
Yours faithfully, CH. DARWIN.
[The next letter refers to his 'Biographical Sketch of an Infant,' written from notes made 37 years previously, and published in 'Mind,' July, 1877. The article attracted a good deal of attention, and was translated at the time in 'Kosmos,' and the 'Revue Scientifique,' and has been recently published in Dr. Krause's 'Gesammelte kleinere SchrifteN von Charles Darwin,' 1887:]