Down, April 12th [1857].

My dear Hooker,

Your letter has pleased me much, for I never can get it out of my head, that I take unfair advantage of your kindness, as I receive all and give nothing. What a splendid discussion you could write on the whole subject of variation! The cases discussed in your last note are valuable to me (though odious and damnable), as showing how profoundly ignorant we are on the causes of variation. I shall just allude to these cases, as a sort of sub-division of polymorphism a little more definite, I fancy, than the variation of, for instance, the Rubi, and equally or more perplexing.

I have just been putting my notes together on variations apparently due to the immediate and direct action of external causes; and I have been struck with one result. The most firm sticklers for independent creation admit, that the fur of the same species is thinner towards the south of the range of the same species than to the north–that the same shells are brighter-coloured to the south than north; that the same [shell] is paler-coloured in deep water–that insects are smaller and darker on mountains–more livid and testaceous near sea–that plants are smaller and more hairy and with brighter flowers on mountains: now in all such, and other cases, distinct species in the two zones follow the same rule, which seems to me to be most simply explained by species, being only strongly marked varieties, and therefore following the same laws as recognised and admitted varieties. I mention all this on account of the variation of plants in ascending mountains; I have quoted the foregoing remark only generally with no examples, for I add, there is so much doubt and dispute what to call varieties; but yet I have stumbled on so many casual remarks on varieties of plants on mountains being so characterised, that I presume there is some truth in it. What think you? Do you believe there is any tendency in varieties, as generally so-called, of plants to become more hairy and with proportionally larger and brighter-coloured flowers in ascending a mountain?

I have been interested in my “weed garden,” of 3 x 2 feet square: I mark each seedling as it appears, and I am astonished at the number that come up, and still more at the number killed by slugs, etc. Already 59 have been so killed; I expected a good many, but I had fancied that this was a less potent check than it seems to be, and I attributed almost exclusively to mere choking, the destruction of the seedlings. Grass-seedlings seem to suffer much less than exogens…

Charles Darwin to J.D. Hooker.

Moor Park, Farnham [April (?) 1857].

My dear Hooker,

Your letter has been forwarded to me here, where I am undergoing hydropathy for a fortnight, having been here a week, and having already received an amount of good which is quite incredible to myself and quite unaccountable. I can walk and eat like a hearty Christian, and even my nights are good. I cannot in the least understand how hydropathy can act as it certainly does on me. It dulls one’s brain splendidly; I have not thought about a single species of any kind since leaving home. Your note has taken me aback; I thought the hairiness, etc., of Alpine species was generally admitted; I am sure I have seen it alluded to a score of times. Falconer was haranguing on it the other day to me. Meyen or Gay, or some such fellow (whom you would despise), I remember, makes some remark on Chilian Cordillera plants. Wimmer has written a little book on the same lines, and on varieties being so characterised in the Alps. But after writing to you, I confess I was staggered by finding one man (Moquin-Tandon, I think) saying that Alpine flowers are strongly inclined to be white, and Linnaeus saying that cold makes plants apetalous, even the same species! Are Arctic plants often apetalous? My general belief from my compiling work is quite to agree with what you say about the little direct influence of climate; and I have just alluded to the hairiness of Alpine plants as an exception. The odoriferousness would be a good case for me if I knew of varieties being more odoriferous in dry habitats.

I fear that I have looked at the hairiness of Alpine plants as so generally acknowledged that I have not marked passages, so as at all to see what kind of evidence authors advance. I must confess, the other day, when I asked Falconer, whether he knew of individual plants losing or acquiring hairiness when transported, he did not. But now this second, my memory flashes on me, and I am certain I have somewhere got marked a case of hairy plants from the Pyrenees losing hairs when cultivated at Montpellier. Shall you think me very impudent if I tell you that I have sometimes thought that (quite independently of the present case), you are a little too hard on bad observers; that a remark made by a bad observer cannot be right; an observer who deserves to be damned you would utterly damn. I feel entire deference to any remark you make out of your own head; but when in opposition to some poor devil, I somehow involuntarily feel not quite so much, but yet much deference for your opinion. I do not know in the least whether there is any truth in this my criticism against you, but I have often thought I would tell you it.

I am really very much obliged for your letter, for, though I intended to put only one sentence and that vaguely, I should probably have put that much too strongly.

Ever, my dear Hooker, yours most truly,
C. Darwin.

P.S. This note, as you see, has not anything requiring an answer.

The distribution of fresh-water molluscs has been a horrid incubus to me, but I think I know my way now; when first hatched they are very active, and I have had thirty or forty crawl on a dead duck’s foot; and they cannot be jerked off, and will live fifteen and even twenty-four hours out of water.

[The following letter refers to the expedition of the Austrian frigate "Novara"; Lyell had asked my father for suggestions.]

Down, November 4th [1856].

My dear Hooker,

I thank you more cordially than you will think probable, for your note. Your verdict (On the MS. relating to geographical distribution.) 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…

Charles Darwin to J.D. Hooker.

Down, November 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 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 a 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 species 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 ‘convertible 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…

Charles Darwin to J.D. Hooker.

December 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.

Charles Darwin to Asa Gray.

Down, January 1st [1857?].

My dear Dr Gray,

I have received the second part of your paper (‘Statistics of the Flora of the Northern United States.’ “Silliman’s Journal”, 1857.), 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 compliment (“From some investigations of his own, this sagacious naturalist inclines to think that [the species of] large genera range over a larger area than the species of small genera do.”–Asa Gray, loc. cit.): 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 dioecious, monoecious 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. (See ‘Origin,’ Edition i., page 100.)

With hearty thanks, your most troublesome friend,
C. Darwin.

[September, 1856].

“In the course of some weeks, you unfortunate wretch, you will have my MS. on one point of Geographical Distribution. I will however, never ask such a favour again; but in regard to this one piece of MS., it is of infinite importance to me for you to see it; for never in my life have I felt such difficulty what to do, and I heartily wish I could slur the whole subject over.”

In a letter to Sir J.D. Hooker (June, 1856), the following characteristic passage occurs, suggested, no doubt, by the kind of work which his chapter on Geographical Distribution entailed:

“There is wonderful ill logic in his [E. Forbes'] famous and admirable memoir on distribution, as it appears to me, now that I have got it up so as to give the heads in a page. Depend on it, my saying is a true one, viz., that a compiler is a great man, and an original man a commonplace man. Any fool can generalise and speculate; but, oh, my heavens! To get up at second hand a New Zealand Flora, that is work.”

Charles Darwin to W.D. Fox.

October 3 [1856].

…I remember you protested against Lyell’s advice of writing a sketch of my species doctrines. Well, when I began I found it such unsatisfactory work that I have desisted, and am now drawing up my work as perfect as my materials of nineteen years’ collecting suffice, but do not intend to stop to perfect any line of investigation beyond current work. Thus far and no farther I shall follow Lyell’s urgent advice. Your remarks weighed with me considerably. I find to my sorrow it will run to quite a big book. I have found my careful work at pigeons really invaluable, as enlightening me on many points on variation under domestication. The copious old literature, by which I can trace the gradual changes in the breeds of pigeons has been extraordinarily useful to me. I have just had pigeons and fowls alive from the Gambia! Rabbits and ducks I am attending to pretty carefully, but less so than pigeons. I find most remarkable differences in the skeletons of rabbits. Have you ever kept any odd breeds 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 (November 10th) 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 my present materials allow without waiting to perfect them. And this much acceleration I owe to you."]

Charles Darwin to J.D. Hooker.

Down, Sunday [October 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 good-bye; 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!!! (The mud in such cases often contains seeds, so that plants are thus transported.) Adios.

Your insane and perverse friend,
C. Darwin.

Down, August 5th [1856].

…I quite agree about Lyell’s letters to me, which, though to me interesting, have afforded me no new light. Your letters, under the geological point of view, have been more valuable to me. You cannot imagine how earnestly I wish I could swallow continental extension, but I cannot; the more I think (and I cannot get the subject out of my head), the more difficult I find it. If there were only some half-dozen cases, I should not feel the least difficulty; but the generality of the facts of all islands (except one or two) having a considerable part of their productions in common with one or more mainlands utterly staggers me. What a wonderful case of the Epacridae! It is most vexatious, also humiliating, to me that I cannot follow and subscribe to the way in which you strikingly put your view of the case. I look at your facts (about Eucalyptus, etc.) as damning against continental extension, and if you like also damning against migration, or at least of enormous difficulty. I see the ground of our difference (in a letter I must put myself on an equality in arguing) lies, in my opinion, that scarcely anything is known of means of distribution. I quite agree with A. De Candolle’s (and I dare say your) opinion that it is poor work putting together the merely possible means of distribution; but I see no other way in which the subject can be attacked, for I think that A. De Candolle’s argument, that no plants have been introduced into England except by man’s agency, [is] of no weight. I cannot but think that the theory of continental extension does do some little harm as stopping investigation of the means of dispersal, which, whether negative or positive, seems to me of value; when negatived, then every one who believes in single centres will have to admit continental extensions.

…I see from your remarks that you do not understand my notions (whether or no worth anything) about modification; I attribute very little to the direct action of climate, etc. I suppose, in regard to specific centres, we are at cross purposes; I should call the kitchen garden in which the red cabbage was produced, or the farm in which Bakewell made the Shorthorn cattle, the specific centre of these species! And surely this is centralisation enough!

I thank you most sincerely for all your assistance; and whether or no my book may be wretched, you have done your best to make it less wretched. Sometimes I am in very good spirits and sometimes very low about it. My own mind is decided on the question of the origin of species; but, good heavens, how little that is worth!…

[With regard to "specific centres," a passage from a letter dated July 25, 1856, by Sir Charles Lyell to Sir J.D. Hooker (‘Life' ii. page 216) is of interest:

“I fear much that if Darwin argues that species are phantoms, he will also have to admit that single centres of dispersion are phantoms also, and that would deprive me of much of the value which I ascribe to the present provinces of animals and plants, as illustrating modern and tertiary changes in physical geography.”

He seems to have recognised, however, that the phantom doctrine would soon have to be faced, for he wrote in the same letter: “Whether Darwin persuades you and me to renounce our faith in species (when geological epochs are considered) or not, I foresee that many will go over to the indefinite modifiability doctrine.”

In the autumn my father was still working at geographical distribution, and again sought the aid of Sir J.D. Hooker.

Down, July 20th [1856].

…It is not a little egotistical, but I should like to tell you (and I do not think I have) how I view my work. Nineteen years (!) ago it occurred to me that whilst otherwise employed on Natural History, I might perhaps do good if I noted any sort of facts bearing on the question of the origin of species, and this I have since been doing. Either species have been independently created, or they have descended from other species, like varieties from one species. I think it can be shown to be probable that man gets his most distinct varieties by preserving such as arise best worth keeping and destroying the others, but I should fill a quire if I were to go on. To be brief, I assume that species arise like our domestic varieties with much extinction; and then test this hypothesis by comparison with as many general and pretty well-established propositions as I can find made out,–in geographical distribution, geological history, affinities, etc., etc. And it seems to me that, supposing that such hypothesis were to explain such general propositions, we ought, in accordance with the common way of following all sciences, to admit it till some better hypothesis be found out. For to my mind to say that species were created so and so is no scientific explanation, only a reverent way of saying it is so and so. But it is nonsensical trying to show how I try to proceed in the compass of a note. But as an honest man, I must tell you that I have come to the heterodox conclusion that there are no such things as independently created species–that species are only strongly defined varieties. I know that this will make you despise me. I do not much underrate the many huge difficulties on this view, but yet it seems to me to explain too much, otherwise inexplicable, to be false. Just to allude to one point in your last note, viz., about species of the same genus generally having a common or continuous area; if they are actual lineal descendants of one species, this of course would be the case; and the sadly too many exceptions (for me) have to be explained by climatal and geological changes. A fortiori on this view (but on exactly same grounds), all the individuals of the same species should have a continuous distribution. On this latter branch of the subject I have put a chapter together, and Hooker kindly read it over. I thought the exceptions and difficulties were so great that on the whole the balance weighed against my notions, but I was much pleased to find that it seemed to have considerable weight with Hooker, who said he had never been so much staggered about the permanence of species.

I must say one word more in justification (for I feel sure that your tendency will be to despise me and my crotchets), that all my notions about how species change are derived from long continued study of the works of (and converse with) agriculturists and horticulturists; and I believe I see my way pretty clearly on the means used by nature to change her species and adapt them to the wondrous and exquisitely beautiful contingencies to which every living being is exposed…

Charles Darwin to J.D. Hooker.

Down, July 30th 1856.

My dear Hooker,

Your letter is of much value to me. I was not able to get a definite answer from Lyell (On the continental extensions of Forbes and others.), as you will see in the enclosed letters, though I inferred that he thought nothing of my arguments. Had it not been for this correspondence, I should have written sadly too strongly. You may rely on it I shall put my doubts moderately. There never was such a predicament as mine: here you continental extensionists would remove enormous difficulties opposed to me, and yet I cannot honestly admit the doctrine, and must therefore say so. I cannot get over the fact that not a fragment of secondary or palaeozoic rock has been found on any island above 500 or 600 miles from a mainland. You rather misunderstand me when you think I doubt the possibility of subsidence of 20,000 or 30,000 feet; it is only probability, considering such evidence as we have independently of distribution. I have not yet worked out in full detail the distribution of mammalia, both identical and allied, with respect to the one element of depth of the sea; but as far as I have gone, the results are to me surprisingly accordant with my very most troublesome belief in not such great geographical changes as you believe; and in mammalia we certainly know more of means of distribution than in any other class. Nothing is so vexatious to me, as so constantly finding myself drawing different conclusions from better judges than myself, from the same facts.

I fancy I have lately removed many (not geographical) great difficulties opposed to my notions, but God knows it may be all hallucination.

Please return Lyell’s letters.

What a capital letter of Lyell’s that to you is, and what a wonderful man he is. I differ from him greatly in thinking that those who believe that species are not fixed will multiply specific names: I know in my own case my most frequent source of doubt was whether others would not think this or that was a God-created Barnacle, and surely deserved a name. Otherwise I should only have thought whether the amount of difference and permanence was sufficient to justify a name: I am, also, surprised at his thinking it immaterial whether species are absolute or not: whenever it is proved that all species are produced by generation, by laws of change, what good evidence we shall have of the gaps in formations. And what a science Natural History will be, when we are in our graves, when all the laws of change are thought one of the most important parts of Natural History.

I cannot conceive why Lyell thinks such notions as mine or of ‘Vestiges,’ will invalidate specific centres. But I must not run on and take up your time. My MS. will not, I fear, be copied before you go abroad. With hearty thanks.

Ever yours,
C. Darwin.

P.S.–After giving much condensed, my argument versus continental extensions, I shall append some such sentence, as that two better judges than myself have considered these arguments, and attach no weight to them.