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of rabbits, and can you give me any details? One other question : You used to keep hawks ; do you at all know, after eating a bird, how soon after they throw up the pellet?

No subject gives me so much trouble and doubt and difficulty as the means of dispersal of the same species of terrestrial productions on the oceanic islands. Land mollusca drive me mad, and I cannot anyhow get their eggs to experimentise their power of floating and resistance to the injurious action of salt water. I will not apologise for writing so much about my own doings, as I believe you will like to hear. Do sometime, I beg you, let me hear how you get on in health ; and if so inclined, let me have some words on call-ducks. My dear Fox, yours affectionately,

CH. DARWIN.

(With regard to his book he wrote (Nov. 1oth) to Sir Charles Lyell :

"I am working very steadily at my big book; I have found it quite impossible to publish any preliminary essay or sketch ; but am doing my work as completely as Irly present materials allow without waiting to perfect them. And this much acceleration I owe to you."]

C. Darwin to J. D. Hooker.

Down, Sunday (Oct. 1856.] · MY DEAR HOOKER, — The seeds are come all safe, many thanks for them. I was very sorry to run away so soon and miss any part of my most pleasant evening; and I ran away like a Goth and Vandal without wishing Mrs. Hooker goodbye; but I was only just in time, as I got on the platform the train had arrived.

I was particularly glad of our discussion after dinner ; fighting a battle with you always clears my mind wonderfully. I groan to hear that A. Gray agrees with you about the condition of Botanical Geography. All I know is that if you had had to search for light in Zoological Geography you would by contrast, respect your own subject a vast deal more than you now do. The hawks have behaved like gentlemen, and have cast up pellets with lots of seeds in them; and I have just had a parcel of partridge's feet well caked with mud!!!* Adios. Your insane and perverse friend,

C. Darwin.

C. Darwin to J. D. Hooker,

Down, Nov. 4th (1856). My dear Hooker, I thank you more cordially than you will think probable, for your note. Your verdict has been a great relief. On my honour I had no idea whether or not you would say it was (and I knew you would say it very kindly) so bad, that you would have begged me to have burnt the whole. To my own mind my MS. relieved me of some few difficulties, and the difficulties seemed to me pretty fairly stated, but I had become so bewildered with conflicting facts, evidence, reasoning and opinions, that I felt to myself that I had lost all judgment. Your general verdict is incomparably more favourable than I had anticipated. ...

C. Darwin to J. D. IIooker.

Down, Nov. 23rd (1856). MY DEAR HOOKER, I fear I shall weary you with letters, but do not answer this, for in truth and without flattery, I so value your letters, that after a heavy batch, as of late, I feel that I have been extravagant and have drawn too much money, and shall therefore have to stint myself on another occasion.

When I sent my MS. I felt strongly that some preliminary

* The mud in such cases often contains seeds, so that plants are thus transported.

t On the MS. relating to geographical distribution.

1856.]

NATURAL SELECTION.

445

questions on the causes of variation ought to have been sent you. Whether I am right or wrong in these points is quite a separate question, but the conclusion which I have come to, quite independently of geographical distribution, is that external conditions (to which naturalists so often appeal) do by themselves very little. How much they do is the point of all others on which I feel myself very weak. I judge from the facts of variation under domestication, and I may yet get more light. But at present, after drawing up a rough copy on this subject, my conclusion is that external conditions do extremely little, except in causing mere variability. This mere variability (causing the child not closely to resemble its parent) I look at as very different from the formation of a marked variety or new species. (No doubt the variability is governed by laws, some of which I am endeavouring very obscurely to trace.) The formation of a strong variety or species I look at as almost wholly due to the selection of what may be incorrectly called chance variations or variability. This power of selection stands in the most direct relation to time, and in the state of nature can be only excessively slow. Again, the slight differences selected, by which a race or spe. cies is at last formed, stands, as I think can be shown (even with plants, and obviously with animals), in a far more important relation to its associates than to external conditions. Therefore, according to my principles, whether right or wrong, I cannot agree with your proposition that time, and altered conditions, and altered associates, are “cor.vertible terms.' I look at the first and the last as far more important: time being important only so far as giving scope to selection. God knows whether you will perceive at what I am driving. I shall have to discuss and think more about your difficulty of the temperate and sub-arctic forms in the S. hemisphere than I have yet done. But I am inclined to think that I am right (if my general principles are right), that there would be little tendency to the formation of a new species, during the period of migration, whether shorter or longer, though considerable variability may have supervened. ...

C. Darwin to J. D. Hooker.

Dec. 24th (1856) ... How I do wish I lived near you to discuss matters with. I have just been comparing definitions of species, and stating briefly how systematic naturalists work out their subjects. Aquilegia in the Flora Indica was a capital example for me. It is really laughable to see what different ideas are prominent in various naturalists' minds, when they speak of "species ; " in some, resemblance is everything and descent of little weight-in some, resemblance seems to go for nothing, and Creation the reigning idea-in some, descent is the key,-in some, sterility an unfailing test, with others it is not worth a farthing. It all comes, I believe, from trying to define the undefinable. I suppose you have lost the odd black seed from the birds' dung, which germinated,-anyhow, it is not worth taking trouble over. I have now got about a dozen seeds out of small birds’ dung. Adios, My dear Hooker, ever yours,

C. DARWIN.

C. Darwin to Asa Gray.

Down, Jan. Ist [1857?}. My dear Dr Gray,—I have received the second part of your paper,* and though I have nothing particular to say, I must send you my thanks and hearty admiration. The whole paper strikes me as quite exhausting the subject, and I quite fancy and flatter myself I now appreciate the character of your Flora. What a difference in regard to Europe your remark in relation to the genera makes! I have been eminently glad to see your conclusion in regard to the species of large genera widely ranging; it is in strict conformity with the results I have worked out in several ways. It is of great importance to my notions. By the way you have paid me a great

* Statistics of the Flora of the Northern U. States.' Silliman's Journal, 1857

1857.1

TREES AND SHRUBS.

447

compliment : * to be simply mentioned even in such a paper I consider a very great honour. One of your conclusions makes me groan, viz., that the line of connection of the strictly alpine plants is through Greenland. I should extremely like to see your reasons published in detail, for it “riles” me (this is a proper expression, is it not ?) dreadfully. Lyell told me, that Agassiz having a theory about when Saurians were first created, on hearing some careful observations opposed to this, said he did not believe it, “ for Nature never lied." I am just in this predicament, and repeat to you that, “Nature never lies,” ergo, theorisers are always right. . ..

Overworked as you are, I dare say you will say that I am an odious plague; but here is another suggestion! I was led by one of my wild speculations to conclude (though it has nothing to do with geographical distribution, yet it has with your statistics) that trees would have a strong tendency to have flowers with diæcious, monacious or polygamous structure. Seeing that this seemed so in Persoon, I took one little British Flora, and discriminating trees from bushes according to Loudon, I have found that the result was in species, genera and families, as I anticipated. So I sent my notions to Hooker to ask him to tabulate the New Zealand Flora for this end, and he thought my result sufficiently curious, to do so; and the accordance with Britain is very striking, and the more so, as he made three classes of trees, bushes, and herbaceous plants. (He says further he shall work the Tasmanian Flora on the same principle.) The bushes hold an intermediate position between the other two classes. It seems to me a curious relation in itself, and is very much so, if my theory and explanation are correct. With hearty thanks, your most troublesome friend,

C. DARWIN.

*“From some investigations of his own, this sagacious naturalist inclines to think that large genera range over a larger area than the species of small genera do."-Asa Gray, loc. cit.

† See 'Origin,' Ed. i., p. 100.

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