I will trouble you with only one other question. In discussion with Mr.
Gould, I found that in most of the genera of birds which range over the whole or greater part of the world, the individual species have wider ranges, thus the Owl is mundane, and many of the species have very wide ranges. So I believe it is with land and fresh-water sh.e.l.ls--and I might adduce other cases. Is it not so with Cryptogamic plants; have not most of the species wide ranges, in those genera which are mundane? I do not suppose that the converse holds, viz.--that when a species has a wide range, its genus also ranges wide. Will you so far oblige me by occasionally thinking over this? It would cost me vast trouble to get a list of mundane phanerogamic genera and then search how far the species of these genera are apt to range wide in their several countries; but you might occasionally, in the course of your pursuits, just bear this in mind, though perhaps the point may long since have occurred to you or other Botanists. Geology is bringing to light interesting facts, concerning the ranges of sh.e.l.ls; I think it is pretty well established, that according as the geographical range of a species is wide, so is its persistence and duration in time. I hope you will try to grudge as little as you can the trouble of my letters, and pray believe me very truly yours,
C. DARWIN.
P.S. I should feel extremely obliged for your kind offer of the sketch of Humboldt; I venerate him, and after having had the pleasure of conversing with him in London, I shall still more like to have any portrait of him.
[What follows is quoted from Sir J. Hooker"s notes. "The next act in the drama of our lives opens with personal intercourse. This began with an invitation to breakfast with him at his brother"s (Erasmus Darwin"s) house in Park Street; which was shortly afterwards followed by an invitation to Down to meet a few brother Naturalists. In the short intervals of good health that followed the long illnesses which oftentimes rendered life a burthen to him, between 1844 and 1847, I had many such invitations, and delightful they were. A more hospitable and more attractive home under every point of view could not be imagined--of Society there were most often Dr. Falconer, Edward Forbes, Professor Bell, and Mr. Waterhouse--there were long walks, romps with the children on hands and knees, music that haunts me still. Darwin"s own hearty manner, hollow laugh, and thorough enjoyment of home life with friends; strolls with him all together, and interviews with us one by one in his study, to discuss questions in any branch of biological or physical knowledge that we had followed; and which I at any rate always left with the feeling that I had imparted nothing and carried away more than I could stagger under. Latterly, as his health became more seriously affected, I was for days and weeks the only visitor, bringing my work with me and enjoying his society as opportunity offered. It was an established rule that he every day pumped me, as he called it, for half an hour or so after breakfast in his study, when he first brought out a heap of slips with questions botanical, geographical, etc., for me to answer, and concluded by telling me of the progress he had made in his own work, asking my opinion on various points. I saw no more of him till about noon, when I heard his mellow ringing voice calling my name under my window--this was to join him in his daily forenoon walk round the sand-walk. On joining him I found him in a rough grey shooting-coat in summer, and thick cape over his shoulders in winter, and a stout staff in his hand; away we trudged through the garden, where there was always some experiment to visit, and on to the sand-walk, round which a fixed number of turns were taken, during which our conversation usually ran on foreign lands and seas, old friends, old books, and things far off to both mind and eye.
"In the afternoon there was another such walk, after which he again retired till dinner if well enough to join the family; if not, he generally managed to appear in the drawing-room, where seated in his high chair, with his feet in enormous carpet shoes, supported on a high stool--he enjoyed the music or conversation of his family."
Here follows a series of letters ill.u.s.trating the growth of my father"s views, and the nature of his work during this period.]
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. Aga.s.siz 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,"
ent.i.tled "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-p.e.c.k.e.r, 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 acc.u.mulating 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 amus.e.m.e.nt 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.
Farewell, C. DARWIN.
CHARLES DARWIN TO L. JENYNS (BLOMEFIELD). Down, October 12th, [1845].
My dear Jenyns,
Thanks for your note. I am sorry to say I have not even the tail-end of a fact in English Zoology to communicate. I have found that even trifling observations require, in my case, some leisure and energy, both of which ingredients I have had none to spare, as writing my Geology thoroughly expends both. I had always thought that I would keep a journal and record everything, but in the way I now live I find I observe nothing to record. Looking after my garden and trees, and occasionally a very little walk in an idle frame of mind, fills up every afternoon in the same manner. I am surprised that with all your parish affairs, you have had time to do all that which you have done. I shall be very glad to see your little work (Mr. Jenyns" "Observations in Natural History." It is prefaced by an Introduction on "Habits of observing as connected with the study of Natural History," and followed by a "Calendar of Periodic Phenomena in Natural History," with "Remarks on the importance of such Registers." My father seems to be alluding to this Register in the P.S. to the letter dated October 17, 1846.) (and proud should I have been if I could have added a single fact to it).
My work on the species question has impressed me very forcibly with the importance of all such works as your intended one, containing what people are pleased generally to call trifling facts. These are the facts which make one understand the working or economy of nature. There is one subject, on which I am very curious, and which perhaps you may throw some light on, if you have ever thought on it; namely, what are the checks and what the periods of life,--by which the increase of any given species is limited. Just calculate the increase of any bird, if you a.s.sume that only half the young are reared, and these breed: within the NATURAL (i.e., if free from accidents) life of the parents the number of individuals will become enormous, and I have been much surprised to think how great destruction MUST annually or occasionally be falling on every species, yet the means and period of such destruction is scarcely perceived by us.
I have continued steadily reading and collecting facts on variation of domestic animals and plants, and on the question of what are species.
I have a grand body of facts, and I think I can draw some sound conclusions. The general conclusions at which I have slowly been driven from a directly opposite conviction, is that species are mutable, and that allied species are co-descendants from common stocks. I know how much I open myself to reproach for such a conclusion, but I have at least honestly and deliberately come to it. I shall not publish on this subject for several years. At present I am on the Geology of South America. I hope to pick up from your book some facts on slight variations in structure or instincts in the animals of your acquaintance.
Believe me, ever yours, C. DARWIN.
CHARLES DARWIN TO L. JENYNS (REV. L. BLOMEFIELD). Down, [1845?].
My dear Jenyns,
I am very much obliged to you for the trouble you have taken in having written me so long a note. The question of where, when, and how the check to the increase of a given species falls appears to me particularly interesting, and our difficulty in answering it shows how really ignorant we are of the lives and habits of our most familiar species. I was aware of the bare fact of old birds driving away their young, but had never thought of the effect you so clearly point out, of local gaps in number being thus immediately filled up. But the original difficulty remains; for if your farmers had not killed your sparrows and rooks, what would have become of those which now immigrate into your parish? in the middle of England one is too far distant from the natural limits of the rook and sparrow to suppose that the young are thus far expelled from Cambridgeshire. The check must fall heavily at some time of each species" life; for, if one calculates that only half the progeny are reared and bred, how enormous is the increase! One has, however, no business to feel so much surprise at one"s ignorance, when one knows how impossible it is without statistics to conjecture the duration of life and percentage of deaths to births in mankind. If it could be shown that apparently the birds of pa.s.sage WHICH BREED HERE and increase, return in the succeeding years in about the same number, whereas those that come here for their winter and non-breeding season annually, come here with the same numbers, but return with greatly decreased numbers, one would know (as indeed seems probable) that the check fell chiefly on full-grown birds in the winter season, and not on the eggs and very young birds, which has appeared to me often the most probable period. If at any time any remarks on this subject should occur to you, I should be most grateful for the benefit of them.
With respect to my far distant work on species, I must have expressed myself with singular inaccuracy if I led you to suppose that I meant to say that my conclusions were inevitable. They have become so, after years of weighing puzzles, to myself ALONE; but in my wildest day-dream, I never expect more than to be able to show that there are two sides to the question of the immutability of species, i.e. whether species are DIRECTLY created or by intermediate laws (as with the life and death of individuals). I did not approach the subject on the side of the difficulty in determining what are species and what are varieties, but (though, why I should give you such a history of my doings it would be hard to say) from such facts as the relationship between the living and extinct mammifers in South America, and between those living on the Continent and on adjoining islands, such as the Galapagos. It occured to me that a collection of all such a.n.a.logous facts would throw light either for or against the view of related species being co-descendants from a common stock. A long searching amongst agricultural and horticultural books and people makes me believe (I well know how absurdly presumptuous this must appear) that I see the way in which new varieties become exquisitely adapted to the external conditions of life and to other surrounding beings. I am a bold man to lay myself open to being thought a complete fool, and a most deliberate one. From the nature of the grounds which make me believe that species are mutable in form, these grounds cannot be restricted to the closest-allied species; but how far they extend I cannot tell, as my reasons fall away by degrees, when applied to species more and more remote from each other.
Pray do not think that I am so blind as not to see that there are numerous immense difficulties in my notions, but they appear to me less than on the common view. I have drawn up a sketch and had it copied (in 200 pages) of my conclusions; and if I thought at some future time that you would think it worth reading, I should, of course, be most thankful to have the criticism of so competent a critic. Excuse this very long and egotistical and ill-written letter, which by your remarks you had led me into, and believe me,
Yours very truly, C. DARWIN.
CHARLES DARWIN TO L. JENYNS (BLOMEFIELD). Down, October 17th, 1846.
Dear Jenyns,
I have taken a most ungrateful length of time in thanking you for your very kind present of your "Observations." But I happened to have had in hand several other books, and have finished yours only a few days ago.
I found it very pleasant reading, and many of your facts interested me much. I think I was more interested, which is odd, with your notes on some of the lower animals than on the higher ones. The introduction struck me as very good; but this is what I expected, for I well remember being quite delighted with a preliminary essay to the first number of the "Annals of Natural History." I missed one discussion, and think myself ill-used, for I remember your saying you would make some remarks on the weather and barometer, as a guide for the ignorant in prediction.
I had also hoped to have perhaps met with some remarks on the amount of variation in our common species. Andrew Smith once declared he would get some hundreds of specimens of larks and sparrows from all parts of Great Britain, and see whether, with finest measurements, he could detect any proportional variations in beaks or limbs, etc. This point interests me from having lately been skimming over the absurdly opposite conclusions of Gloger and Brehm; the one making half-a-dozen species out of every common bird, and the other turning so many reputed species into one.
Have you ever done anything of this kind, or have you ever studied Gloger"s or Brehm"s works? I was interested in your account of the martins, for I had just before been utterly perplexed by noticing just such a proceeding as you describe: I counted seven, one day lately, visiting a single nest and sticking dirt on the adjoining wall. I may mention that I once saw some squirrels eagerly splitting those little semi-transparent spherical galls on the back of oak-leaves for the maggot within; so that they are insectivorous. A Cychrus rostratus once squirted into my eyes and gave me extreme pain; and I must tell you what happened to me on the banks of the Cam, in my early entomological days: under a piece of bark I found two Carabi (I forget which), and caught one in each hand, when lo and behold I saw a sacred Panagaeus crux major! I could not bear to give up either of my Carabi, and to lose Panagaeus was out of the question; so that in despair I gently seized one of the Carabi between my teeth, when to my unspeakable disgust and pain the little inconsiderate beast squirted his acid down my throat, and I lost both Carabi and Panagaeus! I was quite astonished to hear of a terrestrial Planaria; for about a year or two ago I described in the "Annals of Natural History" several beautifully coloured terrestrial species of the Southern Hemisphere, and thought it quite a new fact.
By the way, you speak of a sheep with a broken leg not having flukes: I have heard my father aver that a fever, or any SERIOUS ACCIDENT, as a broken limb, will cause in a man all the intestinal worms to be evacuated. Might not this possibly have been the case with the flukes in their early state?
I hope you were none the worse for Southampton (The meeting of the British a.s.sociation.); I wish I had seen you looking rather fatter. I enjoyed my week extremely, and it did me good. I missed you the last few days, and we never managed to see much of each other; but there were so many people there, that I for one hardly saw anything of any one. Once again I thank you very cordially for your kind present, and the pleasure it has given me, and believe me,
Ever most truly yours, C. DARWIN.
P.S.--I have quite forgotten to say how greatly interested I was with your discussion on the statistics of animals: when will Natural History be so perfect that such points as you discuss will be perfectly known about any one animal?
CHARLES DARWIN TO J.D. HOOKER. Malvern, June 13 [1849].