The Life and Letters of Charles Darwin – Day 131 of 188

Charles Darwin to J.D. Hooker.

Down [1844].

…The conclusion, which I have come at is, that those areas, in which species are most numerous, have oftenest been divided and isolated from other areas, united and again divided; a process implying antiquity and some changes in the external conditions. This will justly sound very hypothetical. I cannot give my reasons in detail; but the most general conclusion, which the geographical distribution of all organic beings, appears to me to indicate, is that isolation is the chief concomitant or cause of the appearance of new forms (I well know there are some staring exceptions). Secondly, from seeing how often the plants and animals swarm in a country, when introduced into it, and from seeing what a vast number of plants will live, for instance in England, if kept free from weeds, and native plants, I have been led to consider that the spreading and number of the organic beings of any country depend less on its external features, than on the number of forms, which have been there originally created or produced. I much doubt whether you will find it possible to explain the number of forms by proportional differences of exposure; and I cannot doubt if half the species in any country were destroyed or had not been created, yet that country would appear to us fully peopled. With respect to original creation or production of new forms, I have said that isolation appears the chief element. Hence, with respect to terrestrial productions, a tract of country, which had oftenest within the late geological periods subsided and been converted into islands, and reunited, I should expect to contain most forms.

But such speculations are amusing only to one self, and in this case useless, as they do not show any direct line of observation: if I had seen how hypothetical [is] the little, which I have unclearly written, I would not have troubled you with the reading of it. Believe me,–at last not hypothetically,

Yours very sincerely,
C. Darwin.

Charles Darwin to J.D. Hooker.

Down, 1844.

…I forget my last letter, but it must have been a very silly one, as it seems I gave my notion of the number of species being in great degree governed by the degree to which the area had been often isolated and divided; I must have been cracked to have written it, for I have no evidence, without a person be willing to admit all my views, and then it does follow; but in my most sanguine moments, all I expect, is that I shall be able to show even to sound Naturalists, that there are two sides to the question of the immutability of species;–that facts can be viewed and grouped under the notion of allied species having descended from common stocks. With respect to books on this subject, I do not know of any systematical ones, except Lamarck’s, which is veritable rubbish; but there are plenty, as Lyell, Pritchard, etc., on the view of the immutability. Agassiz lately has brought the strongest argument in favour of immutability. Isidore G. St. Hilaire has written some good Essays, tending towards the mutability-side, in the ‘Suites a Buffon,’ entitled “Zoolog. Generale.” Is it not strange that the author, of such a book as the ‘Animaux sans Vertebres,’ should have written that insects, which never see their eggs, should will (and plants, their seeds) to be of particular forms, so as to become attached to particular objects. The other, common (specially Germanic) notion is hardly less absurd, viz. that climate, food, etc., should make a Pediculus formed to climb hair, or wood-pecker, to climb trees. I believe all these absurd views arise, from no one having, as far as I know, approached the subject on the side of variation under domestication, and having studied all that is known about domestication. I was very glad to hear your criticism on island-floras and on non-diffusion of plants: the subject is too long for a letter: I could defend myself to some considerable extent, but I doubt whether successfully in your eyes, or indeed in my own…

Charles Darwin to J.D. Hooker.

Down [July, 1844].

…I am now reading a wonderful book for facts on variation–Bronn, ‘Geschichte der Natur.’ It is stiff German: it forestalls me, sometimes I think delightfully, and sometimes cruelly. You will be ten times hereafter more horrified at me than at H. Watson. I hate arguments from results, but on my views of descent, really Natural History becomes a sublimely grand result-giving subject (now you may quiz me for so foolish an escape of mouth)…I must leave this letter till to-morrow, for I am tired; but I so enjoy writing to you, that I must inflict a little more on you.

Have you any good evidence for absence of insects in small islands? I found thirteen species in Keeling Atoll. Flies are good fertilizers, and I have seen a microscopic Thrips and a Cecidomya take flight from a flower in the direction of another with pollen adhering to them. In Arctic countries a bee seems to go as far N. as any flower…

Charles Darwin to J.D. Hooker.

Shrewsbury [September, 1845].

My dear Hooker,

I write a line to say that Cosmos (A translation of Humboldt’s ‘Kosmos.’) arrived quite safely [N.B. One sheet came loose in Part I.}, and to thank you for your nice note. I have just begun the introduction, and groan over the style, which in such parts is full half the battle. How true many of the remarks are (i.e. as far as I can understand the wretched English) on the scenery; it is an exact expression of one’s own thoughts.

I wish I ever had any books to lend you in return for the many you have lent me…

All of what you kindly say about my species work does not alter one iota my long self-acknowledged presumption in accumulating facts and speculating on the subject of variation, without having worked out my due share of species. But now for nine years it has been anyhow the greatest amusement to me.

Farewell, my dear Hooker, I grieve more than you can well believe, over our prospect of so seldom meeting.

I have never perceived but one fault in you, and that you have grievously, viz. modesty; you form an exception to Sydney Smith’s aphorism, that merit and modesty have no other connection, except in their first letter.

C. Darwin.

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