To August Weismann   29 February 1872

Down, Beckenham, Kent

Feb. 29th. 1872

My dear Sir

I am rejoiced to hear that your eye-sight is somewhat better; but I fear that work with the microscope is still out of your power.1 I have often thought with sincere sympathy how much you must have suffered from your grand line of embryological research having been stopped.2 It was very good of you to use your eyes in writing to me. I have just received your essay; but as I am now staying in London for the sake of rest, and as german is at all times very difficult to me, I shall not be able to read your essay for some little time. I am however very curious to learn what you have to say on isolation and on periods of variation.3 I thought much about isolation when I wrote in Chap. IV on the circumstances favourable to Nat. Selection.4 No doubt there remains an immense deal of work to do on Artbildung.5 I have only opened a path for others to enter, and in the course of time, to make a broad and clear high-road. I am especially glad that you are turning your attention to sexual selection. I have in this country hardly found any naturalists who agree with me on this subject, even to a moderate extent. They think it absurd that a female bird should be able to appreciate the spendid plumage of the male; but it would take much to persuade me that the pea-cock does not spread his gorgeous tail in the presence of the female in order to fascinate or excite her. The case no doubt is much more difficult with insects. I fear that you will find it difficult to experiment on diurnal Lepidoptera in confinement, for I have never heard of any of these breeding in this state.6 I was extremely pleased at hearing from Fritz Müller that he liked my chapter on Lepidoptera in the Descent of Man more than any other part, excepting the chapter on morals.7

With the most sincere respect and good wishes for your improved eyesight, I remain, my dear Sir | Yours very faithfully | Ch. Darwin

Copy

1
Weismann’s letter has not been found. From 1864, Weismann had suffered from a rare disease of the retina in his left eye; his eyesight gradually improved, but only fully recovered in 1874 (Petrunkevitch 1963, pp. 21–2).
2
Weismann’s early work on embryogenesis in flies (Diptera) led to his discovery of imaginal discs, sacs of embryonic cells from which the adult head and thorax arose (see Weismann 1864). CD’s copy of a summary in English of Weismann’s discovery (Lowne 1869) is in the Darwin Pamphlet Collection–CUL.
3
CD’s heavily annotated copy of Weismann’s Ueber den Einfluss der Isolirung auf die Artbildung (On the influence of isolation on the formation of species; Weismann 1872) is in the Darwin Library–CUL (see Marginalia 1: 857–60). In his letter to Weismann of 22 October 1868 (Correspondence vol. 16), CD commented that Moritz Wagner greatly overrated the necessity of isolation in the formation of species. In Weismann 1872, Weismann strongly opposed Wagner’s view that geographic isolation was the main cause of speciation. For more on the debate between Wagner and Weismann, see Weissman 2010.
4
See Origin 6th ed., pp. 81–5.
5
Artbildung: species formation (German).
6
In his missing letter, Weismann evidently discussed his plan to study the causes of differences in colour in butterflies that were seasonally dimorphic. The results of his investigation appeared in Weismann 1875.
7
See Correspondence vol. 19, letter from Fritz Müller, 14 June 1871 and nn. 1 and 2.

Please cite as “DCP-LETT-8228,” in Ɛpsilon: The Charles Darwin Collection accessed on 5 June 2025, https://epsilon.ac.uk/view/dcp-data/letters/DCP-LETT-8228