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Darwin Correspondence Project

From C. G. Semper   6 December 1878


6. dec. 1878.

my dear mr. darwin!

your two so very kind letters have given me the greatest pleasure, and i thank you very much for having taken such a trouble in answering my question. i am glad to see, that i did not misunderstand you in supposing, that mr. wagner had misrepresented your views with respect to his theory.1

the question arises now, what to do? i shall have to refer to wagners views in my work on the influence of external conditions of existence on animals; and i am bound to state, that to my understanding his theory appears to be only an integral part of your more general theory; yet he asserts in the most positive way, that you yourself appear to incline most decidedly in favour of his views.2 not having any right, to use your letters against wagner, i fear, all german readers of my work will say, and mr wagner certainly will do so, that i had no ground for interpreting your unknown words in your letters to wagner in a way different from that, to which wagner thinks himself justified. now if you will entitle me, to make use of your letters in the discussion of these matters, i certainly shall use them in the most discretionary way; if you do not wish to be drawn into the discussion directly, please tell me so candidly and i assure you, that not a single word of what you wrote me, will appear in print.

i thank you also for the many valuable remarks, you gave me in your letters on the subject of the influence of isolation and external conditions on animals and i am glad to see, that you do not regard this latter as altogether valueless.3 for i must confess, that i attach greater importance to this agency, than you seem to be inclined to do. supposing then, that selection and external conditions have acted together, it seems to be the principal question, to ask how much of the ultimate effect may have been due to the one or the other. and this question can be answered, as far as i see, only by keeping both causes apart in experimental researches. to direct the attention of the speculating zoologists to such experimental work and to induce them, to abstain for some time at least from speculating in such a random way as has been done f. i. by weissmann or by jaeger, to try to do this, is the main object of the work, i am writing now.4 during this time, i fear, i shall not have the time for treating the isolation question as thoroughly, as i would like to do. but after having finished the book in question, i hope to get more leisure, than i have just now and in that case, it is my firm intention to discuss the wagnerian hypothesis to some extent and on the same ground, restricted as it is, which has been taken by wagner for exemplifying.

remember me please to your family and believe me to be | yours devotedly | C. Semper5


See letters to C. G. Semper, 26 November [1878] and 30 November 1878. Semper’s letter concerning the differences between CD’s and Moritz Wagner’s views on the development of new species through geographical isolation has not been found.
In his essay ‘Der Naturproceß der Artbildung’ (The natural process of species formation; Wagner 1875), Wagner had frequently referred to examples from CD’s work to support his argument that isolation was necessary in the formation of new species, and intimated that while CD underestimated the importance of isolation, he did not discount it (see ibid., pp. 475, 490–1, and passim). Semper’s work, Die natürlichen Existenzbedingungen der Thiere (The natural conditions of existence of animals; Semper 1880), was published in 1880 and translated into English in 1881 (Semper 1881). Semper discussed geographical isolation and CD’s and Wagner’s views in Semper 1880, 2: 110–13 (see also Semper 1881, pp. 288–93). CD gave his copy of the German edition to the library of the Linnean Society; his annotated copy of the English edition is in the Darwin Library–CUL.
In his letter to Semper of 30 November 1878, CD noted that the effect of different conditions in an isolated district could account, at least in part, for modification of species.
August Weismann had opposed Wagner’s views on isolation in his work, Ueber den Einfluss der Isolirung auf die Artbildung (On the influence of isolation on the formation of species; Weismann 1872); Gustav Jäger had similarly criticised Wagner (Jäger 1874, pp. 52, 90).
Semper wrote this letter using the typewriter that CD had given him, which only had upper-case letters (see letter from C. G. Semper, 5 October 1878 and n. 1). The corrections (in lower-case) and signature were handwritten).


Jäger, Gustav. 1874. In Sachen Darwin’s insbesondere contra Wigand. Ein Beitrag zur Rechtfertigung und Fortbildung der Umwandlungslehre. Stuttgart: E. Schweizerbart’sche Verlagshandlung (E. Koch).

Semper, Carl. 1880. Die natürlichen Existenzbedingungen der Thiere. 2 vols. Leipzig: F. A. Brockhaus.

Semper, Karl. 1881. The natural conditions of existence as they affect animal life. London: C. Kegan Paul & Co.

Wagner, Moritz. 1875. Der Naturproceß der Artbildung. Das Ausland, 31 May 1875, pp. 425–8; 7 June 1875, pp. 449–52; 14 June 1875, pp. 473–5; 21 June 1875, pp. 490–3; 28 June 1875, pp. 513–16; 19 July 1875, pp. 570–5; 26 July 1875, pp. 589–93.

Weismann, August. 1872. Ueber den Einfluss der Isolirung auf die Artbildung. Leipzig: Wilhelm Engelmann.


Asks whether he may use CD’s letters in his work [Die natürlichen Existenzbedingungen der Thiere (1880)] in order to show that Moritz Wagner has misrepresented CD’s views.

Discusses the influence of isolation and external conditions on animals, and the relative importance of the direct effect of external conditions and of selection in bringing about change.

Letter details

Letter no.
Carl Gottfried Semper
Charles Robert Darwin
Sent from
Source of text
DAR 202: 120
Physical description
1p †

Please cite as

Darwin Correspondence Project, “Letter no. 11776,” accessed on 14 June 2021,