To Ernst Haeckel   18 August [1866]

Down. | Bromley. | Kent. S.E.

Aug 18

My dear Sir

I received a few days ago a sheet of your new work, & have read it with great interest.1 You confer on my book, the “Origin of Species”, the most magnificent eulogium which it has ever received, & I am most truly gratified, but I fear if this part of your work is ever criticized, your reviewer will say that you have spoken much too strongly.2 Your abstract seems to me wonderfully clear & good; & one little fact shews me how clearly you understand my views, namely your bringing prominently forward, which no one else has ever done, the fact & the cause of Divergence of Character.3 Oddly enough, as it now appears to me, it was many years before I clearly saw the necessity of admitting a tendency to divergence of character, & some more years until I could see the explanation.4

I have read with much interest your discussion on Inheritance &c; & all the more so as I give in my next work, which will not be published for half a year, several chapters on this & other allied subjects.5 So that I shall feel very curious to read your remaining chapters when published; but it is a terrible evil to me that I cannot read more than one or two pages at a time of German, even when written as clearly as is your book.

I suppose you have seen Prof. Claus new work on Copepoda in which he discusses individual variability, & alludes to your work; I have been interested by it.6 I heartily congratulate you that your great undertaking is so nearly completed & with my cordial thanks for the great honour which you have done me & with a full belief that you will do excellent service in the cause which we have both at heart, I remain my dear sir | yours very sincerely Ch. Darwin

LS(A)

Endorsement: ‘1866’

1
The reference is to a proof-sheet of Haeckel’s Generelle Morphologie (Haeckel 1866). CD’s annotated copy of the book, which he later received, is in the Darwin Library–CUL (see letter from Ernst Haeckel, 19 October 1866 and n. 3; see also Marginalia 1: 355–7). For Haeckel’s discussions of his work on the book, see Correspondence vols. 12 and 13.
2
In a section about the history of the theory of descent, Haeckel wrote that Origin was the book through which CD founded a new era in general morphology and physiology and also in anthropology and the whole of science in general (Haeckel 1866, 2: 163).
3
See Haeckel 1866, 2: 249–56, and Marginalia 1: 357. For CD’s discussion of divergence, see Origin, pp. 111–26.
4
CD’s notes on divergence and classification are in DAR 205.5. See Correspondence vols. 3 and 6 for some early discussions of the principle of divergence.
5
See Haeckel 1866, 2: 170–90. CD refers to Variation, which was published in January 1868 (Freeman 1977). In Variation 2: 397 n., CD cited Haeckel 1866, 2: 170, on the simplest form of inheritance.
6
Carl Friedrich Claus’s monograph on the copepods of Nice (Claus 1866) presented a classification scheme influenced by Darwinian transmutation theory; it focused particularly on the role of environmental factors in determining morphological features in the sub-class Copepoda. CD had earlier recommended it to Joseph Dalton Hooker (see letter to J. D. Hooker, 3 and 4 August [1866] and n. 20). Claus referred to Haeckel’s conclusions on variability within the copepod family, Corycaeidae, but did not cite a specific work (Claus 1866, p. 2).

Manuscript Alterations and Comments

1.7 , which … done,] interl in CD’s hand
2.1 &c] interl in CD’s hand

Please cite as “DCP-LETT-5193,” in Ɛpsilon: The Charles Darwin Collection accessed on 5 June 2025, https://epsilon.ac.uk/view/dcp-data/letters/DCP-LETT-5193