CD writes on geographical distribution – "a grand game of chess with the world for a board".
Gives his hypothetical explanation why zoology of Cape [of Good Hope] is not so peculiar as its botany: it was once a group of islands – later united.
Tries hard to set forth the difficulties of his [species] theory.
Tells CJFB in confidence of his theory of the glacial epoch and its effect on plant distribution, such as identical species being found on summits of mountains in the tropics. Invites him to attack his "doctrine".
Down Bromley Kent
My dear Bunbury
You are quite right, I do take a very great interest about the Cape Flora & Fauna, & I thank you much for your letter, which, as all yours do, has pleased & instructed me much.— I have lately been especially attending to Geograph. Distrib, & most splendid sport it is,—a grand game of chess with the world for a Board. The fact you allude to about the zoology (at least mammifers) of the Cape not being nearly so peculiar as the Botany has often struck me much: I think the most probable hypothetical explanation is that it was long a group of islands, since united with the continent allowing the vertebrata to enter.—
Thank you about the Colletia, I called on Lindley, but
I am very glad to hear you are still thinking of Madeira; there seems to me much to be
done there yet; but I hear from M
You speak in far too flattering a way about my work, in which I will persevere; & I will endeavour (eheu how difficult) “to be cautious & candid & avoid dogmatism”. My determination to put difficulties, as far as I can see them, on both sides is a great aid towards candour; because I console myself, when finding some great difficulty, in endeavouring to put is as forcibly as I can.— I am trying many little experiments, but they are hardly worth telling, though some I am sure will bear on distribution & I think on aquatic plants.
As you say you like scientific chat, & your kind letter makes me sure that you will not think me an egotistical bore, I will tell you of a theory I am maturing (by the way please do not mention it to anyone, for 2 directly opposite reasons, viz whether valueless or valuable). As glacial action extended over whole of Europe, & in Himmalaya, on both sides of N. America & both sides of Southern S. America & I believe in N. Zealand, within very late times (existence of recent species); I cannot but think the whole world must have been rather colder during the Glacial Epoch: (I know I ought to be able to show that the glacial action was actually & absolutely coincident in North & South, & this I cannot do, nor can I here enter in details to show how far I can show them coincident)
At this period I look at the intertropical plants as somewhat distressed, but not (or only a few) exterminated.— Under these conditions I consider it probable that some of the warmer temperate plants would spread into the Tropics, whilst the arctic plants reached the foot of the Alps & Pyrenees. (according to poor Forbes' view; by the way I had this part of the theory written out., 4 years before Forbes published!)
Some, I consider it possible might cross the Tropics & survive at C. of Good Hope, T. del Fuego & S. Australia; but within the Tropics, when warmth returned, all would be exterminated, except such as crawled up mountains, as in Ceylon, Neilgherries, Java, Organ mountains in Brazil. This theory, I conceive, explains certain aquatic productions in S. hemisphere &c &c. (& European Fish at C. of Good Hope)— But on the view that species change, it throws, I think, far more light on the analogous, but not identical species, on the summits of the above named mountains. Of course I cannot enter in details (& you would not care to hear them) on this subject, which I am sure in some degree would render the view more probable than it will seem to you at first.—
You will probably object, why have so many more Northern species & forms gone to the south, than southern forms come to the north; I can explain this only on a pure hypothesis of cold having come on first from the north; but there has been some migration from south to north, as of Australian forms on Mountains of Borneo. And I am sure I have notes of a few S. African forms, as wanderers across the Tropics, into N. Africa & Europe: is not this so with Gladiolus, Stapelia(?). Can you help me in this, either identical species, or allied forms, of well marked S. African forms? By the way I look at Abyssinia, during the cold period, as the channel of communication; for some, (as I know from Richard) very northern temperate species of plants are found there; & some S. African forms likewise.—
There, I am sure, you will agree that I have prosed enough on my own doctrines; which I may have to give up, but I strongly suspect that the theory is a sound vessel & will hold water. I look at the vegetation of the Tropics, during the cold period, as having been somewhat like the vegetation described by Hooker at foot of Himmalaya, as essentially Tropical, but with an odd mixture of Temperate forms & even identical species, before they became mostly modified.—
What will you say to such a dose of speculation! You will exclaim, “he is a pretty fellow to talk of caution”!—
Pray believe me | Your's very sincerely | Charles Darwin
If at any time you are inclined to write pray attack my doctrine.—
With respect to diffusion of water plants in very distant regions, it seems,
as far as my doctrine is concerned, sufficient answer that the same species of water
plants in the same continent are very widely diffused, & whatever the means of
diffusion may be, the same means w
- f1 1856.f1Dated by the relationship to the letter from C. J. F. Bunbury, 16 April 1856.
- f2 1856.f2Letter from C. J. F. Bunbury, 16 April 1856.
- f3 1856.f3See letters from C. J. F. Bunbury, 7 February 1856 and 16 April 1856.
- f4 1856.f4Lowe 1856. See letter from R. T. Lowe, 12 April 1856. Richard Thomas Lowe was also at work on A manual flora of Madeira (Lowe 1857[–72]).
- f5 1856.f5In 1856, CD began experiments on the transport of plants, seeds, and ova by birds. Experiments on the germination of seeds from pond mud were commenced on 6 April 1856 (DAR 157a).
- f6 1856.f6CD gave a fuller discussion of this theory in Natural selection, pp. 534–54, and Origin, pp. 365–82.
- f7 1856.f7Edward Forbes published this view in E. Forbes 1846. CD gave a similar explanation in the 1842 sketch of his species theory, expanded in the essay of 1844 (Foundations, pp. 31 and 165–9). For a discussion of the views of Forbes and CD on Arctic–alpine floras, see J. Browne 1983, pp. 117–27.
- f8 1856.f8Richard .
- f9 1856.f9No further letters from Bunbury about CD's theories in 1856 have been found, but Bunbury did record the substance of a conversation on species on 20 June 1856, when CD visited Bunbury in London (F. J. Bunbury ed. 1891–3, Middle Life 2: 413–14). With reference to the topics discussed in this letter, Bunbury wrote (p. 414):
He spoke of his theory (which he had before mentioned to me by letter) that an interchange of plants, to a certain degree, may have taken place between Europe and the Cape of Good Hope, during the glacial period, when a much colder climate than the present existed beyond certain parallels of latitude, in both hemispheres. In accordance with his doctrine of the mutability of species, he supposes that the representative species in either hemisphere (e.g. the species of Dianthus at the Cape, and those of Gladiolus in Europe), may be modified forms originating from the opposite hemisphere in which their respective genera have their head quarters. His chief difficulty is, that there are so many more representatives of northern forms at the Cape than representatives of southern forms in Europe; as if the migration had taken place chiefly from north to south.
- f10 1856.f10A. de Candolle 1855, 1: 499–500 and 604.