I do not know whether you will consider me a very troublesome man, but I have just finished your book ('Comparative Longevity.'), and can not resist telling you how the whole has much interested me. No doubt, as you say, there must be much speculation on such a subject, and certain results can not be reached; but all your views are highly suggestive, and to my mind that is high praise. I have been all the more interested as I am now writing on closely allied though not quite identical points. I was pleased to see you refer to my much despised child, 'Pangenesis,' who I think will some day, under some better nurse, turn out a fine stripling. It has also pleased me to see how thoroughly you appreciate (and I do not think that this is general with the men of science) H. Spencer; I suspect that hereafter he will be looked at as by far the greatest living philosopher in England; perhaps equal to any that have lived. But I have no business to trouble you with my notions. With sincere thanks for the interest which your work has given me, I remain, yours very faithfully, CH. DARWIN. [The next letter refers to Mr. Wallace's 'Natural Selection' (1870), a collection of essays reprinted with certain alterations of which a list is given in the volume:] CHARLES DARWIN TO A.R. WALLACE. Down, April 20 [1870]. My dear Wallace, I have just received your book, and read the preface. There never has been passed on me, or indeed on any one, a higher eulogium than yours. I wish that I fully deserved it. Your modesty and candour are very far from new to me. I hope it is a satisfaction to you to reflect--and very few things in my life have been more satisfactory to me--that we have never felt any jealousy towards each other, though in one sense rivals. I believe that I can say this of myself with truth, and I am absolutely sure that it is true of you. You have been a good Christian to give a list of your additions, for I want much to read them, and I should hardly have had time just at present to have gone through all your articles. Of course I shall immediately read those that are new or greatly altered, and I will endeavour to be as honest as can reasonably be expected. Your book looks remarkably well got up. Believe me, my dear Wallace, to remain, Yours very cordially, CH. DARWIN. [Here follow one or two letters indicating the progress of the 'Descent of Man;' the woodcuts referred to were being prepared for that work:] CHARLES DARWIN TO A. GUNTHER. (Dr. Gunther, Keeper of Zoology in the British Museum.) March 23, [1870?]. Dear Gunther,