From A. R. Wallace   19 November 1866

9, St. Mark’s Crescent, | Regent’s Park, N.W.

Novr. 19th. 1866

Dear Darwin

Many thanks for the 4th. Ed. of the “Origin”,1 which I am glad to see grows so vigorously at each moult, although it undergoes no metamorphosis. How curious it is that Dr. Wells should so clearly have seen the principle of Nat. Selectn. 50 years ago and that it should have struck no one that it was a great principle of universal application in Nature!2

We are going to have a discussion on “Mimicry, as producing abnormal sexual characters” at the Entomological tonight.3 I have a butterfly (a Diadema) of which the female is metallic blue, the male dusky brown contrary to the rule in all other species of the genus, & in almost all insects;—but the explanation is easy;—it mimics a metallic blue Euplœa, and so gets a protection perhaps more efficient than its allies derive from their sombre colours, & which females require much more than males. I read a paper on this at the B. Assn.4 Have you the report published at Nottingham in a volume by Dr. Robertson, if so you can tell me if my paper is printed at full?5

I suppose you have read Agassiz’ marvellous theory of the,—Gt. Amazonian Glacier! 2000 miles long!!!6 I presume that will be a little too much even for you. I have been writing a little popular paper on “Glacial Theories” for the Quarterly Journ. of Science of Jan. next in which I stick up for Glaciers in N. America and Ice bergs in the Amazon!7

I was very glad to hear from Lubbock that your health is permanently improved.8 I hope therefore you will be able to give us a volume per. annum of your “op. mag.”, with all the facts as you now have them, leaving additions to come in new editions. 9

I am working a little at another family of my butterflies & find the usual interesting & puzzling cases of variation, but no such strange phenomena as in the Papilionidæ. 10

With best wishes | Believe me | My dear Darwin | Yours very faithfully | Alfred R. Wallace—

C. Darwin Esq.

1
Wallace’s name appears on CD’s presentation list for the fourth edition of Origin (Correspondence vol. 14, Appendix IV).
2
CD had added a reference to William Charles Wells and his essay ‘An account of a female of the white race of mankind, part of whose skin resembles that of a negro; with some observations on the causes of the differences in colour and form between the white and negro races of men’, published in W. C. Wells 1818, to the historical sketch at the beginning of the fourth edition of Origin (pp. xiv–xv). See letter from Asa Gray, 7 August 1866 and n. 4.
3
An account of the discussion was reported in the Transactions of the Entomological Society of London (Journal of the Proceedings) 3d ser. 5 (1865–7): xxxvi–xli (19 November 1866).
4
In his paper ‘On reversed sexual characters in a butterfly’ (A. R. Wallace 1866a, p. 186), Wallace suggested the name Diadema anomala (now Hypolimnas anomala) to highlight the fact that it was the female of the species that mimicked the male Euploea midamus. An abstract of the paper (A. R. Wallace 1866b) appeared in the Report of the thirty-sixth meeting of the British Association for the Advancement of Science held at Nottingham.
5
Wallace refers to William Tindal Robertson and Robertson ed. 1866, in which the full text of Wallace’s paper and some comments were reproduced (A. R. Wallace 1866a).
6
The reference is to Louis Agassiz’s article in Atlantic Monthly (J. L. R. Agassiz 1866a), in which he put forward a theory that the Amazon valley had been covered by a glacier (for more on the theory, see, for example, the letter to Charles Lyell, 8[–9] September [1866] and n. 6).
7
In his paper ‘Ice marks in north Wales. With a sketch of glacial theories and controversies’ (A. R. Wallace 1867), Wallace discussed the evidence for glaciers in the area around Snowdon and Cader Idris in Wales. He argued that there was no evidence for Agassiz’s claim that a glacier once covered the Amazon valley, but suggested that some evidence existed that icebergs once floated over a submerged Amazonian plain (ibid., p. 41).
8
John Lubbock. On CD’s improved health, see the letter to W. D. Fox, 24 August [1866].
9
The ‘opus magnum’ or ‘great work’ to which Wallace refers was the three-part work on variation in domestic and wild species and the principle of natural selection, of which Variation was originally intended to be the first part (see Variation 1: 3–9 for CD’s outline of all three proposed works).
10
For Wallace’s earlier work on Malay Papilionidae, see Correspondence vol. 12 and A. R. Wallace 1864b.

Please cite as “DCP-LETT-5280,” in Ɛpsilon: The Charles Darwin Collection accessed on 5 June 2025, https://epsilon.ac.uk/view/dcp-data/letters/DCP-LETT-5280