Charles Darwin an Ernst Haeckel, Down, 12. April 
Down. | Bromley. | Kent. S. E.
My dear Sir a
I hope you have returned home well in health, & that you have reaped a rich harvest in natural science. I have been intending for some time to write to you about your great work, of which I have lately been reading a good deal. But it makes me almost mad with vexation that I am able to read imperfectly only 2 or 3 pages at a time. The whole book wd be infinitely interesting & || useful to me. What has struck me most is the singular clearness with which all the lesser principles & the general philosophy of the subject have been thought out by you & methodically arranged. Your criticism on the struggle for existence offers a good instance how much clearer your thoughts are than mine.
Your whole discussion on dysteologie has struck me as particularly good. But it is hopeless to specify this or that part; the whole seems to me excellent. It is equally hopeless to attempt thanking you for all the honours with which you so repeatedly crown me. I hope that you will not think me impertinent if I make one criticism: some of your remarks on various authors seem to me too severe; but I cannot || judge well on this head from being so poor a German scholar. I have however heard complaints from several excellent authorities & admirers of your work on the severity of your criticisms. This seems to me very unfortunate for I have long observed that much severity leads the reader to take the side of the attacked person. I can call to mind distinct instances in which severity produced directly the opposite effect to what was intended. I feel sure that our good friend Huxley, though he has much influence, wd have had far more if he had been more moderate & less frequent in his attacks. As you will surely play a great part in science, let me as an older man earnestly beg you to reflect on what I have ventured || to say. I know that it is easy to preach & if I had the power of writing with severity I dare say I shd triumph in turning poor devils inside out & exposing all their imbecility. Nevertheless I am convinced that this power does no good, only causes pain. I may add that as we daily see men arriving at opposite conclusions from the same premises it seems to me doubtful policy to speak too positively on any complex subject however much a man may feel convinced of the truth of his own conclusions. Now can you forgive me for my freedom? Though we have met only once I write to you as to an old friend, for I feel thus towards you.
With respect to my own book on Variation under domestication I am making slow, but sure progress in correcting || the proofs. I fear that it will interest you but little, & you will be struck how badly I have arranged some of the subjects which you have discussed. The chief use of my book will be in the large accumulation of facts by which certain propositions are I think established. I have indulged in one lengthened hypothesis, but whether this will interest you or any one else, I cannot even conjecture. I hope before long you will write to me & tell me how you are & what you have been doing & believe me my dear Häckel
yours very sincerely
a gestr.: I