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Darwin Correspondence Project

To C. J. F. Bunbury   9 February [1860]1

Down Bromley Kent

Feb. 9th

My dear Bunbury

I am very much obliged to you for writing to me at such length; for I value your opinion much. Ever since our sojourn at Capel Kurig2 I have formed (if you will not think it impertinent in me to say so) the highest opinion of your knowledge, acuteness & judgment. Therefore I thank you much for your praise of my Book. I am sorry, but not in the least surprised that you do not go a little further with me.3 I changed so slowly myself that I am indeed surprised at anyone becoming a convert.—

I will just run through some of the salient points in your letter: with respect to admitting representative species to be descendants of one species & not extending the same view to whole classes, the point seems to me to turn whether you think the explanation which I offer of the classification of all Beings, the principles of Homology & of Embryology, & Rudimentary organs are satisfactorily explained.4 The explanation seems to me to be nearly satisfactory; & this being so, I can to myself allow of no difficulties in imagining what were the steps of transition to weigh against the understanding such large classes of facts.— It is curious how differently different men view the same subject; Asa Gray thinks the Hybrid Chr. one of strongest in Book!5 But he says (& I quite agree) more wants making out why varieties are not sterile when crossed. But this seems hopeless till we can say on what difference two close species are to certain extent fertile, & another two close species absolutely sterile.

With respect to Nat. Selection not being a “vera causa”; it seems to me fair in Philosophy to invent any hypothesis & if it explains many phenomena it comes in time to be admitted as real.6 In your sense the undulatory theory of the hypothetical ether (the undulations themselves being not recognised) is not a vera causa in accounting for all the phenomena of Light. Natural selection seems to me in so far in itself not be quite hypothetical, in as much if there be variability & a struggle for life, I cannot see how it can fail to come into play to some extent. You speak of “Degeneracy”,7 I wish you could give me any instance of a race, kept under the same conditions. & in a moderately large body together degenerating or modifying: this is always assumed as certain; I do not dispute it, but I wish much for some evidence.

The extinction of intermediate forms seems to me explained in Ch. IV & more especially in the Xth Chapt.: if my Principle of Divergence of Character be admitted this almost necessarily follows.

I quite agree with what you say on effect of admission of theory on Systematic work; (see p. 485), not but what I was haunted with endeavouring to guess what cirripedes would be ranked as species by other naturalists.8 I think the importance of theory bears on opening up new fields of enquiry & in giving a rational, instead of theological explanation of many known facts   I am much pleased to hear that you intend reading the Book again. If not too troublesome I shall be most grateful for any other remarks. Your letter is as clear as daylight, & mine, I fear, like a London foggy day.—

Again I thank you heartily for all your kind trouble & believe me | Dear Bunbury | Yours very sincerely | Charles Darwin

As you give up representative species, I suspect & hope that you will go further; but this will depend wholly whether you think the large classes of facts in Ch. XIII are explained by Theory.— See remark (at p 127) where I say “Whether nat. Select. has really thus acted in nature in modifying &c &c must be judged of by the balance of evidence given in the following Chapters”


Dated by the relationship to the letter from C. J. F. Bunbury, 30 January 1860.
CD and Bunbury met in the Welsh village of Capel Curig in 1842 during CD’s expedition to examine the erratic boulders of Caernarvonshire (see Correspondence vol. 2, letter to W. H. Fitton, [c. 28 June 1842]). The occasion is described in Bunbury ed. 1891–3, Early life 1: 367 n.
The portion of the letter from C. J. F. Bunbury, 30 January 1860, in which he addressed this point is now missing. In the terminology of the time, ‘representative’ species were species of similar structure living in different locales; they were said to take the place of, or ‘represent’, each other. Orthodox naturalists believed that such species had been designed with a similar form but created separately for different geographical areas.
CD’s view of the concept of a ‘vera causa’ was primarily derived from John Frederick William Herschel’s discussion in Herschel 1831, a text that he had read while at Cambridge University (see Correspondence vol. 1, letter to W. D. Fox, [15 February 1831], and Ruse 1975). CD’s copy of the work is in the Darwin Library–CUL. Herschel used the notion to define what can legitimately be proposed as the underlying factors on which a phenomenon depends (Herschel 1831, p. 197): They must be veræ causæ, in short, which we can not only show to exist and to act, but the laws of whose action we can derive independently, by direct induction, from experiments purposely instituted; or at least make such suppositions respecting them as shall not be contrary to our experience, and which will remain to be verified by the coincidence of the conclusions we shall deduce from them, with facts.
It was a long-held belief among many naturalists, systematised through the writings of Georges Louis Leclerc, Comte de Buffon, that some modification or variation in species had occurred through the degeneration or ‘falling off’ of an original created type. This concept was especially invoked to explain the production of new varieties of domesticated plants and animals by man. See Roger 1989, pp. 392–401.
CD refers to the passage in Origin, p. 485, in which he stated that some ‘forms now generally acknowledged to be merely varieties may hereafter be thought worthy of specific names, as with the primrose and cowslip’. For CD’s attempts to balance the requirements of taxonomic nomenclature with his views on the genealogical relationships between Cirripedia, see Correspondence vol. 4, especially his letters to Hugh Edwin Strickland, and Appendix II.


Correspondence: The correspondence of Charles Darwin. Edited by Frederick Burkhardt et al. 29 vols to date. Cambridge: Cambridge University Press. 1985–.

Herschel, John Frederick William. 1831. A preliminary discourse on the study of natural philosophy. In Dionysius Lardner’s Cabinet cyclopædia. London. [Vols. 1,2,6,7,8,9]

Origin: On the origin of species by means of natural selection, or the preservation of favoured races in the struggle for life. By Charles Darwin. London: John Murray. 1859.


Responds to CJFB’s criticisms of the Origin [see 2669].

If CD’s theory is a satisfactory explanation of the "principles of Homology, and of Embryology, and Rudimentary organs", the difficulty in imagining the transitions between classes of beings should not weigh against the understanding it provides such large classes of facts. Defends natural selection against criticism that it is not a vera causa. Comments on "Degeneracy", extinction of intermediate forms, and the effect of theory in natural history in opening up new fields of inquiry and giving rational instead of theological explanations of facts.

Letter details

Letter no.
Charles Robert Darwin
Charles James Fox Bunbury, 8th baronet
Sent from
Source of text
Suffolk Record Office, Bury St Edmunds (Bunbury Family Papers E18/700/1/9/6)
Physical description
ALS 4pp

Please cite as

Darwin Correspondence Project, “Letter no. 2690,” accessed on 29 January 2023,

Also published in The Correspondence of Charles Darwin, vol. 8