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Darwin Correspondence Project

To James Dwight Dana   21 December [1856]1

Down Bromley Kent

Dec. 21st

My dear Sir

I am very much obliged for all the trouble you have so kindly taken for me, & for your letter of Nov. 28th.—2 I have been these few last days comparing & thinking over the many definitions of species; & puzzling over the different variability of different forms; & I think I will venture to quote your remark on the “libration” of species.—3 But first let me thank you for your paper on Geological Development:4 everything which you have ever written interests me; but I own this last paper is rather too grand for my digestion; not but that I am very much inclined, from different reasons, to agree with you on antiquity of continents & oceans; & I have lately had some written discussion on subject with Lyell, who differs toto coelo5 from me. In my coral volume,6 I remember coming to same conclusion of continents now & lately having risen, ocean-beds having sunk, & great archipelagoes having oscillated. But I have never satisfied myself on secular refrigeration: I forget whether you have discussed subject, but I never could understand how refrigeration could cause in same area, the prodigious oscillations of level, which we must believe in, during the successive sedimentary formations of Europe.—

What you say about the importance of the infertility of species, when crossed, I quite agree with; & I think those who attribute our domestic varieties to the crossing of ma[n]y primordial forms, greatly underrate the evidence on this question— Nevertheless after a very careful study of all the facts, these facts do not seem to me to make so important a distinction between species & varieties, as I at first thought: I have to a certain extent satisfied my own mind on this head, but whether I shall satisfy anyone else, I know not.— My subject as I treat it, is almost ridiculous in one way; that I never come to any conclusion on any point, without having to advance a heap of difficulties & arguments on the other side. How I wish I had some of your knowledge & powers of work, & my work would be a very different affair.— But I am loth to throw away 19 years collection of facts & observations of my own, & I will do my best.

Dr. A. Gray has sent me his paper,7 & I have had a good deal of correspondence with him on the subject before & since he published.— I admire extremely all that he writes & it seems to me his only fault is too much modesty about his results. A rare fault with a vengeance amongst men of science.

J. Lubbock is going to publish a nice paper on Daphnia— he has made out the spermatozoa, the structure of ephippium, & some facts on double means of procreation, nicely.—8 Prof. Huxley has been at work lately on Crustacea, & believes he has made out in the higher Crustacea the homologues of the cementing apparatus in my old enemies the Cirripedes—9

I have just been looking over your letter again; & your doctrine of species being definite like chemical elements, rubs against me; but I am terribly in want of facts whether variable forms are variable in all places (can you give me any facts?) & all times. Protean genera, like Rubus Rosa &c10 puzzle me greatly. But I am running on at an unreasonable length, so will conclude with thanks & all good wishes, yours sincerely | C. Darwin

P.S. | This morning I have received your note of the 8th,11 & very much obliged I am for it. I am particularly glad to hear about the Cave Rat, for though the case does not differ in any essential respect in its relations from, for instance, an alpine Fauna to the continent in which the mountain stands; the cave animals have always seemed to me an eminently curious instance.

I am, also, very glad to hear your opinion on the parallelism of embryological & palæontological development: I think I am nearly in your frame of mind, strongly inclined to believe in it; only I feel that I want more numerous & striking instances to convince me than those as yet given. I adduced the fact of Chthamalus, merely as case of negative evidence not being trustworthy; as far as development goes it is quite right that the Chthamalinæ shd. appear before the Balaninæ.—12 As my work very much consists in the comparison of the opinions & results of good workers in different branches, I am very glad to hear the opinion of one like yourself, in whom I have so much faith.—

My principle of work is to consider every subject which I can at all master, under this one point of view,—would such & such be the case, if species are descended, like varieties, from a common parent. And according as larger or smaller classes of facts can be thus explained, so should I conclude that species really were, or were not, lineal descendants of other species.—

I forget whether I ever mentioned that I have taken up domestic Pigeons,—thinking it better to study well one group than slightly several.— I am collecting specimens from all quarters of world, & have got all breeds known in Britain alive; & am making skeletons, crossing breeds &c &c.— I mention this on the mere chance of your ever stumbling on any Fancier: if so I shd. much like to hear whether he believes that any breed (or sub-breed rather) has become at all modified or different from those of Europe. It is not likely, but yet worth enquiry. The old Pigeon literature, together with Persian & Indian specimens, has thrown some light on the origin of domestic varieties, which really differ in an astonishing degree.—13


The year is established by the reference to the letter from J. D. Dana, 8 December 1856 (Correspondence vol. 6).
Dana’s letter of 28 November 1856 has not been found.
In the manuscript of his ‘big book’ on species, CD wrote, and then crossed out, ‘Many authors seem to consider that each species was created with a certain fixed amount of variability, or to use an expression in a letter of Prof. Dana, with “its system of librations under the influences of nature to which it may be subject”, & this would include both recognised varieties & individual variations.’ (Natural selection, p. 105.)
Dana’s paper ‘On the plan of development in the geological history of North America’ was published in the American Journal of Science and Arts (Dana 1856); it was also published together with Dana 1855 as a pamphlet, ‘On American geological history’ (New Haven: Ezekiel Hayes, 1856). There is an annotated copy of the pamphlet in the Darwin Pamphlet Collection–CUL. CD wrote on the back, ‘(Very poor Pamphlet)’.
CD refers to Charles Lyell. Toto caelo: completely, utterly (Latin).
Coral reefs.
CD refers to Asa Gray and the first part of A. Gray 1856–7 (‘Statistics of the flora of the northern United States’); see Correspondence vol. 6, letter to Asa Gray, 12 October [1856]. CD’s annotated copy of A. Gray 1856–7 is in DAR 135 (3).
CD refers to John Lubbock and Lubbock 1857.
CD refers to Thomas Henry Huxley and T. H. Huxley 1856–7, 14: 354. See Correspondence vol. 6, letter to T. H. Huxley, 9 December [1856] and n. 7; see also Fossil Cirripedia (1851) and (1854), and Living Cirripedia (1851) and (1854).
See Origin, p. 46, where CD gave Rubus and Rosa as examples of genera in which the species presented ‘an inordinate amount of variation’.
CD had told Dana of a new species of fossil cirripede, in the genus Chthamalus, found in a Cretaceous formation, having previously believed that no cirripedes of that type existed so long ago; see Correspondence vol. 6, letter to J. D. Dana, 29 September [1856]. See also Fossil Cirripedia (1854), p. 5. The fossil cirripede turned out not to be a fossil, however (Southward ed. 1987, p. 47).
CD discussed domestic pigeons in Origin, pp. 20–9. See also Correspondence vol. 6.


Thanks for sending paper on geological development (Dana 1856). Discusses infertility of species. Discusses first part of Asa Gray’s paper (A. Gray 1856–7). Thanks for note on the Cave Rat. Discusses a new species of fossil cirripede, in the genus Chthamalus. Explains his interest in pigeon breeding.

Letter details

Letter no.
Charles Robert Darwin
James Dwight Dana
Source of text
Catherine Barnes (dealer) (2003)

Please cite as

Darwin Correspondence Project, “Letter no. 2020F,” accessed on 27 January 2022,

Also published in The Correspondence of Charles Darwin, vol. 18 (Supplement)