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Darwin Correspondence Project

To Ernst Haeckel   3 July 1868

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

July 3 1868

My dear Häckel

Many thanks for your kind letter of June 22.1

I am astonished at the amount of work which you are doing; but take care of yourself, & remember how easily the brain is injured & how long a time it takes to regain its strength, as I have known in several instances. Thank you much for the present of your two small works. I am particularly glad to receive that on Man, tho’ probably less important under a scientific point of view than the other; for I intend to publish in about a year’s time a short essay on the descent of Man, & this will include a long & full discussion on Sexual Selection. Hence I shall read with much interest your essay on Man, tho’ it will take me some time as I get on so slowly with German.2

Your great work on General Morphology is getting better known in England, & I often see it alluded to. It has lately been reviewed, but not altogether favorably, by Mr Bentham in his Annual address to the Linnean Soc.3

I am very much obliged for your information about the Hare–rabbits.4 I cannot express sufficient astonishment at hearing that the hybrids are fertile inter se. If I did not know that you yourself had examined these animals I shd not have thought the statement that they were hybrids was worth a moment’s consideration. I suppose they are strictly intermediate in character, & I suppose you have attended to such points as the period at which the newly born animals open their eyelids,—the tendency to make burrows,—the number of the mammæ,—the colour & flavour of the flesh when cooked &c. After the discredit which has been thrown upon the French statements I hope you will be very careful, for I must confess I cannot help being sceptical, & therefore I ought not to be honoured by my name being attached to these animals, which if they really are hybrids are by far the most wonderful ever produced.5

I do not in the least doubt the veracity of Dr. Conrad,6 but I have known such cases, as a servant, either out of spite, or thinking to please his master, introduce for a short time a male to a female which would not breed. Might not this have occurred with Dr Conrad? Did he witness the copulation? Forgive my extreme scepticism.—

My health has been worse lately & if I can travel, I shall soon go to the sea for 5 or 6 weeks.—7 With most kind & cordial feelings towards you, | believe me, yours very sincerely | C. Darwin


CD refers to Haeckel’s ‘Monographie der Moneren’ (Monograph on monera; Haeckel 1868a) and ‘Ueber die Entstehung und den Stammbaum des Menschengeschlechts’ (On the origin and descent of the human races; Haeckel 1868b). There are copies in the Darwin Pamphlet Collection–CUL; the pages of Haeckel 1868a are uncut, but Haeckel 1868b is annotated. CD also refers to Descent, which was published in early 1871. CD cited Haeckel 1868b in Descent 1: 199.
In his annual address to the Linnean Society, George Bentham included a detailed discussion of Haeckel’s Generelle Morphologie (Haeckel 1866). He critised some parts as being too speculative or bewildering (Bentham 1868, pp. lxvi, lxxi n.). William Sweetland Dallas had also mentioned Haeckel 1866 in his letter to CD of 9 June 1868.
A claim that hares and rabbits could be induced to breed in captivity, and that the hybrid offspring were fertile with one another for a number of generations, was made in Broca 1858–9, pp. 370–83. However, the principal source of this claim was rejected in Pigeaux 1867, where it was suggested that the supposed hybrids were ‘merely rabbits’, like some other supposed wild hybrids. The author stated that, although it was evidently possible to cross the hare and the rabbit, it had not been established that the offspring were fertile.
Johannes Ernst Conrad.
The Darwin family spent from 17 July to 20 August 1868 at Freshwater on the Isle of Wight (Emma Darwin’s diary (DAR 242)).


Bentham, George. 1868. Anniversary address. [Read 25 May 1868.] Proceedings of the Linnean Society of London (1867–8): lvii–c.

Broca, Paul. 1858–9. Mémoire sur l’hybridité en général, sur la distinction des espèces amimales et sur les métis obtenus par le croisement du lièvre et du lapin. Journal de la Physiologie de l’Homme et des Animaux 1: 432–71, 684–729; 2: 218–58, 345–96.

Descent: The descent of man, and selection in relation to sex. By Charles Darwin. 2 vols. London: John Murray. 1871.

Haeckel, Ernst. 1866. Generelle Morphologie der Organismen. Allgemeine Grundzüge der organischen Formen-Wissenschaft, mechanisch begründet durch die von Charles Darwin reformirte Descendenz-Theorie. 2 vols. Berlin: Georg Reimer.

Pigeaux, Dr. 1867. On the actual state of our information relative to the ‘Leporide’, or hybrid between hare and rabbit. Annals and Magazine of Natural History 3d ser. 20: 75–7.


Thanks for two small works.

Will read essay on man [Entstehung des Menschengeschlechts] with much interest.

Generelle Morphologie reviewed by G. Bentham ["Anniversary Address", Proc. Linn. Soc. Lond. (1867–8): lviii–c].

Extremely sceptical of hare–rabbit hybrid.

Letter details

Letter no.
Charles Robert Darwin
Ernst Philipp August (Ernst) Haeckel
Sent from
Source of text
Ernst-Haeckel-Haus (Bestand A-Abt. 1:1–52/18)
Physical description

Please cite as

Darwin Correspondence Project, “Letter no. 6265,” accessed on 19 May 2021,

Also published in The Correspondence of Charles Darwin, vol. 16