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Darwin Correspondence Project

To Ernst Haeckel   [after 10] August – 8 October [1864]1

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

Aug. Oct 8th.

Dear Sir

I thank you sincerely for your letter2 & the confidence you repose in me. I have been deeply interested in what you say about your poor wife.3 Her expression in the photograph is charming. I can to a certain extent understand what your feelings are, for I am fortunate enough to know what a treasure a wife can be & no one thought is so painful to me as the possibility of surviving her.

As you seem interested about the origin of the “Origin” & I believe do not say so out of mere compliment, I will mention a few points. When I joined the “Beagle” as Naturalist I knew extremely little about Natural History, but I worked hard.4 In South America three classes of facts were brought strongly before my mind: 1stly the manner in which closely allied species replace species in going Southward.

2ndly the close affinity of the species inhabiting the Islands near to S. America to those proper to the Continent. This struck me profoundly, especially the difference of the species in the adjoining islets in the Galapagos Archipelago.5 3rdly the relation of the living Edentata & Rodentia to the extinct species. I shall never forget my astonishment when I dug out a gigantic piece of armour like that of the living Armadillo.6

Reflecting on these facts & collecting analogous ones, it seemed to me probable that allied species were descended from a common parent. But for some years I could not conceive how each form became so excellently adapted to its habits of life. I then began systematically to study domestic productions, & after a time saw clearly that man’s selective power was the most important agent.7 I was prepared from having studied the habits of animals to appreciate the struggle for existence, & my work in Geology gave me some idea of the lapse of past time. Therefore when I happened to read “Malthus on population” the idea of Natural selection flashed on me.8 Of all the minor points, the last which I appreciated was the importance & cause of the principle of Divergence.9 I hope I have not wearied you with this little history of the “Origin”—10

I quite agree with what you say about Kölliker; there is a capital review of him by Huxley in the Number just published of the “Natural History Review”.11 This letter was begun several weeks ago, but I have delayed finishing it from having little strength & other things to do. Will you have the kindness to tell this to Prof. Gegenbaur as an apology for not having thanked him for the honour he has done me in sending me his work. By a strange chance I dissected several months ago the hind foot of a toad & was particularly curious to understand what the additional bones were, & this point I see will now be explained to me.12 As I know from one of the papers which you have sent me that you have attended to Entomostraca it has occurred to me that you might like to have a copy of my Vol. on the Balanidæ, of which I have a spare copy & would with pleasure send it if you wish for it, & will tell me how to forward it.13

With sincere respect | Believe me my dear Sir | yours very faithfully | Charles Darwin


The date range is established by the relationship between this letter and the letter from Ernst Haeckel, 10 August 1864. Emma Darwin wrote the letter and dated it ‘Aug.’; CD signed it and added the date ‘Oct 8th.’
Letter from Ernst Haeckel, 10 August 1864.
See letter from Ernst Haeckel, 10 August 1864 and n. 4. Haeckel’s wife, Anna Sethe, died on 16 February 1864.
CD accompanied Captain Robert FitzRoy on HMS Beagle as his companion and as the ship’s unofficial naturalist between 1832 and 1836 (Freeman 1978); the voyage to South America and around the world is described in Narrative and Journal of researches. See also Correspondence vol. 1. For an assessment of the contribution of the Beagle voyage to CD’s intellectual development, see Sulloway 1985 and Browne 1995.
CD visited the Galápagos archipelago between 15 September and 20 October 1835 (see Journal of researches, pp. 453–78, 2d ed., pp. 372–401, and ‘Beagle’ diary, pp. 333–43). The Beagle collections from the Galápagos islands indicated not only that the majority of land birds were endemic to the archipelago as a whole, but also that some were endemic to specific islands. The results of the analyses he made between 1837 and 1859 of the plant and animal collections from the archipelago led CD to accord great importance to the role of geographical isolation in the production of new species (Origin, pp. 107–8; Natural selection, pp. 254–6, 273–4; Sulloway 1979 and 1984). See also n. 6, below.
CD made this fossil discovery in September 1832 at Punta Alta, near Bahia Blanca, Argentina (see ‘Beagle’ diary, p. 107, and Correspondence vol. 1, letter to Caroline Darwin, 24 October – 24 November [1832] and n. 4, and letter to J. S. Henslow, [c. 26 October –] 24 November [1832]). The fossil armour was subsequently identified by Richard Owen as belonging to Hoplophorus euphractus, a species like a giant armadillo (see Fossil Mammalia, pp. 106–7). CD commented on the discovery of other fossils with armadillo-like coverings in Journal of researches, pp. 181–2. For CD’s assessment of the importance of his South American fossil collections, together with his Galápagos observations, in the later formulation of his theory, see Correspondence vol. 2, Appendix II, entry for 26 June 1837. Sulloway argues that CD saw the evolutionary significance of his Beagle collections only after his ornithological and fossil specimens had been classified by John Gould and Owen (Sulloway 1982b).
For CD’s studies of domesticated plants and animals and his interchanges with plant and animal breeders, which began in the late 1830s, see J. A. Secord 1985. See also Correspondence vol. 2, Appendix V. CD wrote up his conclusions on the consequences of human selection of plants and animals in the first two draft chapters of his ‘big book’ on species (see Natural selection, pp. 25–6); these were expanded and became the two volumes of Variation (Natural selection, p. 1; Freeman 1979, p. 122).
CD refers to Thomas Robert Malthus’s An essay on the principle of population (Malthus 1826), which he read in September 1838 (Notebooks, Notebook D, 134e–5e). The question of the influence of Malthus on CD has been debated extensively; for an overview of this issue see La Vergata 1985, pp. 953–8. CD’s reading notebooks indicate that he studied Malthus’s work, and critiques of Malthus’s work, closely; he re-read Malthus 1826 in 1847 (see Correspondence vol. 4, Appendix IV). There is an annotated copy of Malthus 1826 in the Darwin Library–CUL (see Marginalia 1: 562–3).
CD’s principle of divergence was based on the premises that a locality can support more life if it is occupied by a diversity of life-forms, that the varying offspring of each species will strive to occupy as many and as great a diversity of niches as possible, and that natural selection will tend to favour the evolution of new, specialised varieties. He saw these processes as the origin of the branching relationships between species, genera, families, orders, and classes. CD first discussed this principle in the letter to J. D. Hooker, 22 August [1857], and the letter to Asa Gray, 5 September [1857] (Correspondence vol. 6); see also Origin, pp. 111–126, and Natural selection, pp. 227–50. For a full definition of the principle of divergence and the background to CD’s formulation of it between November 1854 and 1858, see Browne 1980, Ospovat 1981, pp. 170–209, and Kohn 1985. CD made a similar comment about the length of time it had taken him to understand divergence in his letter to George Bentham, 19 June [1863] (Correspondence vol. 11).
CD gave a later description of the origin of his theories in his Autobiography, pp. 118–121.
See letter from Ernst Haeckel, 10 August 1864 and n. 12. Haeckel had criticised Rudolf Albert von Kölliker’s notion that CD’s theory was teleological (Kölliker 1864a, b, and c). CD also refers to Thomas Henry Huxley’s review of Kölliker 1864b and Flourens 1864 ([T. H. Huxley] 1864a; see also letter to T. H. Huxley, 3 October [1864] and n. 2).
Carl Gegenbaur discussed the bones of the hindleg of toads in Gegenbaur 1864, pp. 59–67. CD’s copy of Gegenbaur 1864 is in the Darwin Library–Down (see Marginalia 1: 299); there is an undated note relating to Gegenbaur 1864 in DAR 205.5: 198. CD was interested in the origin of extra digits, or polydactylism, and had been collecting information on the rudimentary sixth toe in batrachians (see Correspondence vol. 11, letters to T. H. Huxley, 16 February [1863] and [after 16 February 1863]). CD may be referring to the toad that he dissected in June 1863 (see Correspondence vol. 11, letter to T. H. Huxley, 27 June [1863]). In Variation, CD cited Gegenbaur’s opinion that the tubercle on the hindfoot of toads resembled an extra digit, but that the resemblance was only superficial (see Variation 2: 13 n.).
Early in 1864, CD had received a copy of Haeckel’s paper on Corycaeidae, a family in the class Entomostraca (Haeckel 1864a). See letter to Ernst Haeckel, 9 March 1864. There is an annotated copy of Haeckel 1864a in the Darwin Pamphlet Collection–CUL. Entomostraca are lower orders of Crustacea and include the Cirripedia or barnacles. CD published two volumes on Balanidae, a family of Cirripedia: Living Cirripedia (1854) and Fossil Cirripedia (1854). See also Correspondence vol. 4, Appendix II.


Can understand EH’s feelings on death of his wife.

CD was impressed by manner in which species in South America are replaced by closely allied ones, by affinity of species inhabiting islands near S. America, and by relation of living Edentata and Rodentia to extinct species. When he read Malthus On population, the idea of natural selection flashed on him.

Agrees with EH’s remarks on Kölliker ["Darwin’sche Schöpfungstheorie", Z. Wiss. Zool. 14 (1864): 174–86].

Asks EH to thank Carl Gegenbaur [for Vergleichende Anatomie der Wirbelthiere (1864)].

Letter details

Letter no.
Charles Robert Darwin
Ernst Philipp August (Ernst) Haeckel
Sent from
Source of text
Ernst-Haeckel-Haus (Bestand A–Abt. 1: 1–52/5)
Physical description

Please cite as

Darwin Correspondence Project, “Letter no. 4631,” accessed on 21 September 2019,

Also published in The Correspondence of Charles Darwin, vol. 12