More Letters of Charles Darwin — Volume 2

2. I cannot see the difficulty about the cessation of the Glacial period.

Between the Miocene and the Pleistocene periods geographical changes occurred which rendered a true Glacial period possible with high excentricity. When the high excentricity passed away the Glacial epoch also passed away in the temperate zone; but it persists in the arctic zone, where, during the Miocene, there were mild climates, and this is due to the persistence of the changed geographical conditions. The present arctic climate is itself a comparatively new and abnormal state of things, due to geographical modification.

As to "epoch" and "period," I use them as synonyms to avoid repeating the same word.

3. Rate of deposition and geological time. Here no doubt I may have gone to an extreme, but my "28 million years" may be anything under 100 millions, as I state. There is an enormous difference between mean and maximum denudation and deposition. In the case of the great faults the upheaval along a given line would itself facilitate the denudation (whether sub-aerial or marine) of the upheaved portion at a rate perhaps a hundred times above the average, just as valleys have been denuded perhaps a hundred times faster than plains and plateaux. So local subsidence might itself lead to very rapid deposition. Suppose a portion of the Gulf of Mexico, near the mouths of the Mississippi, were to subside for a few thousand years, it might receive the greater portion of the sediment from the whole Mississippi valley, and thus form strata at a very rapid rate.

4. You quote the Pampas thistles, etc., against my statement of the importance of preoccupation. But I am referring especially to St. Helena, and to plants naturally introduced from the adjacent continents. Surely if a certain number of African plants reached the island, and became modified into a complete adaptation to its climatic conditions, they would hardly be expelled by other African plants arriving subsequently. They might be so, conceivably, but it does not seem probable. The cases of the Pampas, New Zealand, Tahiti, etc., are very different, where highly developed aggressive plants have been artificially introduced. Under nature it is these very aggressive species that would first reach any island in their vicinity, and, being adapted to the island and colonising it thoroughly, would then hold their own against other plants from the same country, mostly less aggressive in character.

I have not explained this so fully as I should have done in the book. Your criticism is therefore useful.

5. My Chapter XXIII. is no doubt very speculative, and I cannot wonder at your hesitating at accepting my views. To me, however, your theory of hosts of existing species migrating over the tropical lowlands from the N. temperate to the S. temperate zone appears more speculative and more improbable. For where could the rich lowland equatorial flora have existed during a period of general refrigeration sufficient for this? and what became of the wonderfully rich Cape flora, which, if the temperature of tropical Africa had been so recently lowered, would certainly have spread northwards, and on the return of the heat could hardly have been driven back into the sharply defined and very restricted area in which it now exists.

As to the migration of plants from mountain to mountain not being so probable as to remote islands, I think that is fully counterbalanced by two considerations: —

a. The area and abundance of the mountain stations along such a range as the Andes are immensely greater than those of the islands in the N. Atlantic, for example.

b. The temporary occupation of mountain stations by migrating plants (which I think I have shown to be probable) renders time a much more important element in increasing the number and variety of the plants so dispersed than in the case of islands, where the flora soon acquires a fixed and endemic character, and where the number of species is necessarily limited.

No doubt direct evidence of seeds being carried great distances through the air is wanted, but I am afraid can hardly be obtained. Yet I feel the greatest confidence that they are so carried. Take, for instance, the two peculiar orchids of the Azores (Habenaria sp.) What other mode of transit is conceivable? The whole subject is one of great difficulty, but I hope my chapter may call attention to a hitherto neglected factor in the distribution of plants.

Your references to the Mauritius literature are very interesting, and will be useful to me; and I again thank you for your valuable remarks.

LETTER 397. TO J.D. HOOKER.

(397/1. The following letters were written to Sir J.D. Hooker when he was preparing his Address as President of the Geographical Section of the British Association at its fiftieth meeting, at York. The second letter (August 12th) refers to an earlier letter of August 6th, published in "Life and Letters," III., page 246.)

4, Bryanston Street, W., Saturday, 26th {February, 1881}.

I should think that you might make a very interesting address on Geographical Distribution. Could you give a little history of the subject. I, for one, should like to read such history in petto; but I can see one very great difficulty — that you yourself ought to figure most prominently in it; and this you would not do, for you are just the man to treat yourself in a dishonourable manner. I should very much like to see you discuss some of Wallace's views, especially his ignoring the all-powerful effects of the Glacial period with respect to alpine plants. (397/2. "Having been kindly permitted by Mr. Francis Darwin to read this letter, I wish to explain that the above statement applies only to my rejection of Darwin's view that the presence of arctic and north temperate plants in the SOUTHERN HEMISPHERE was brought about by the lowering of the temperature of the tropical regions during the Glacial period, so that even 'the lowlands of these great continents were everywhere tenanted under the equator by a considerable number of temperate forms ("Origin of Species," Edition VI., page 338). My own views are fully explained in Chapter XXIII. of my "Island Life," published in 1880. I quite accept all that Darwin, Hooker, and Asa Gray have written about the effect of the Glacial epoch in bringing about the present distribution of alpine and arctic plants in the NORTHERN HEMISPHERE." — Note by Mr. Wallace.) I do not know what you think, but it appears to me that he exaggerates enormously the influence of debacles or slips and new surface of soil being exposed for the reception of wind-blown seeds. What kinds of seeds have the plants which are common to the distant mountain-summits in Africa? Wallace lately wrote to me about the mountain plants of Madagascar being the same with those on mountains in Africa, and seemed to think it proved dispersal by the wind, without apparently having inquired what sorts of seeds the plants bore. (397/3. The affinity with the flora of the Eastern African islands was long ago pointed out by Sir J.D. Hooker, "Linn. Soc. Journal," VI., 1861, page 3. Speaking of the plants of Clarence Peak in Fernando Po, he says, "The next affinity is with Mauritius, Bourbon, and Madagascar: of the whole 76 species, 16 inhabit these places and 8 more are closely allied to plants from there. Three temperate species are peculiar to Clarence Peak and the East African islands..." The facts to which Mr. Wallace called Darwin's attention are given by Mr. J.G. Baker in "Nature," December 9th, 1880, page 125. He mentions the Madagascar Viola, which occurs elsewhere only at 7,000 feet in the Cameroons, at 10,000 feet in Fernando Po and in the Abyssinian mountains; and the same thing is true of the Madagascar Geranium. In Mr. Wallace's letter to Darwin, dated January 1st, 1881, he evidently uses the expression "passing through the air" in contradistinction to the migration of a species by gradual extension of its area on land. "Through the air" would moreover include occasional modes of transport other than simple carriage by wind: e.g., the seeds might be carried by birds, either attached to the feathers or to the mud on their feet, or in their crops or intestines.)

I suppose it would be travelling too far (though for the geographical section the discussion ought to be far-reaching), but I should like to see the European or northern element in the Cape of Good Hope flora discussed. I cannot swallow Wallace's view that European plants travelled down the Andes, tenanted the hypothetical Antarctic continent (in which I quite believe), and thence spread to South Australia and the Cape of Good Hope.

Moseley told me not long ago that he proposed to search at Kerguelen Land the coal beds most carefully, and was absolutely forbidden to do so by Sir W. Thomson, who said that he would undertake the work, and he never once visited them. This puts me in a passion. I hope that you will keep to your intention and make an address on distribution. Though I differ so much from Wallace, his "Island Life" seems to me a wonderful book.

Farewell. I do hope that you may have a most prosperous journey. Give my kindest remembrances to Asa Gray.

LETTER 398. TO J.D. HOOKER. Down, August 12th, 1881.

...I think that I must have expressed myself badly about Humboldt. I should have said that he was more remarkable for his astounding knowledge than for originality. I have always looked at him as, in fact, the founder of the geographical distribution of organisms. I thought that I had read that extinct fossil plants belonging to Australian forms had lately been found in Australia, and all such cases seem to me very interesting, as bearing on development.

I have been so astonished at the apparently sudden coming in of the higher phanerogams, that I have sometimes fancied that development might have slowly gone on for an immense period in some isolated continent or large island, perhaps near the South Pole. I poured out my idle thoughts in writing, as if I had been talking with you.

No fact has so interested me for a heap of years as your case of the plants on the equatorial mountains of Africa; and Wallace tells me that some one (Baker?) has described analogous cases on the mountains of Madagascar (398/1. See Letter 397, note.)...I think that you ought to allude to these cases.

I most fully agree that no problem is more interesting than that of the temperate forms in the southern hemisphere, common to the north. I remember writing about this after Wallace's book appeared, and hoping that you would take it up. The frequency with which the drainage from the land passes through mountain-chains seems to indicate some general law — viz., the successive formation of cracks and lines of elevation between the nearest ocean and the already upraised land; but that is too big a subject for a note.

I doubt whether any insects can be shown with any probability to have been flower feeders before the middle of the Secondary period. Several of the asserted cases have broken down.

Your long letter has stirred many pleasant memories of long past days, when we had many a discussion and many a good fight.

LETTER 399. TO J.D. HOOKER. Down, August 21st, 1881.

I cannot aid you much, or at all. I should think that no one could have thought on the modification of species without thinking of representative species. But I feel sure that no discussion of any importance had been published on this subject before the "Origin," for if I had known of it I should assuredly have alluded to it in the "Origin," as I wished to gain support from all quarters. I did not then know of Von Buch's view (alluded to in my Historical Introduction in all the later editions). Von Buch published his "Isles Canaries" in 1836, and he here briefly argues that plants spread over a continent and vary, and the varieties in time come to be species. He also argues that closely allied species have been thus formed in the SEPARATE valleys of the Canary Islands, but not on the upper and open parts. I could lend you Von Buch's book, if you like. I have just consulted the passage.

I have not Baer's papers; but, as far as I remember, the subject is not fully discussed by him.

I quite agree about Wallace's position on the ocean and continent question.

To return to geographical distribution: As far as I know, no one ever discussed the meaning of the relation between representative species before I did, and, as I suppose, Wallace did in his paper before the Linnean Society. Von Buch's is the nearest approach to such discussion known to me.

LETTER 400. TO W.D. CRICK.

(400/1. The following letters are interesting not only for their own sake, but because they tell the history of the last of Mr. Darwin's publications — his letter to "Nature" on the "Dispersal of Freshwater Bivalves," April 6th, 1882.)

Down, February 21st, 1882.

Your fact is an interesting one, and I am very much obliged to you for communicating it to me. You speak a little doubtfully about the name of the shell, and it would be indispensable to have this ascertained with certainty. Do you know any good conchologist in Northampton who could name it? If so I should be obliged if you would inform me of the result.

Also the length and breadth of the shell, and how much of leg (which leg?) of the Dytiscus {a large water-beetle} has been caught. If you cannot get the shell named I could take it to the British Museum when I next go to London; but this probably will not occur for about six weeks, and you may object to lend the specimen for so long a time.

I am inclined to think that the case would be worth communicating to "Nature."

P.S. — I suppose that the animal in the shell must have been alive when the Dytiscus was captured, otherwise the adductor muscle of the shell would have relaxed and the shell dropped off.

LETTER 401. TO W.D. CRICK. Down, February 25th, 1882.

I am much obliged for your clear and distinct answers to my questions. I am sorry to trouble you, but there is one point which I do not fully understand. Did the shell remain attached to the beetle's leg from the 18th to the 23rd, and was the beetle kept during this time in the air?

Do I understand rightly that after the shell had dropped off, both being in water, that the beetle's antenna was again temporarily caught by the shell?

I presume that I may keep the specimen till I go to London, which will be about the middle of next month.

I have placed the shell in fresh-water, to see if the valve will open, and whether it is still alive, for this seems to me a very interesting point. As the wretched beetle was still feebly alive, I have put it in a bottle with chopped laurel leaves, that it may die an easy and quicker death. I hope that I shall meet with your approval in doing so.

One of my sons tells me that on the coast of N. Wales the bare fishing hooks often bring up young mussels which have seized hold of the points; but I must make further enquiries on this head.

LETTER 402. TO W.D. CRICK. Down, March 23rd, 1882.

I have had a most unfortunate and extraordinary accident with your shell. I sent it by post in a strong box to Mr. Gwyn Jeffreys to be named, and heard two days afterwards that he had started for Italy. I then wrote to the servant in charge of his house to open the parcel (within which was a cover stamped and directed to myself) and return it to me. This servant, I suppose, opened the box and dropped the glass tube on a stone floor, and perhaps put his foot on it, for the tube and shell were broken into quite small fragments. These were returned to me with no explanation, the box being quite uninjured. I suppose you would not care for the fragments to be returned or the Dytiscus; but if you wish for them they shall be returned. I am very sorry, but it has not been my fault.

It seems to me almost useless to send the fragments of the shell to the British Museum to be named, more especially as the umbo has been lost. It is many years since I have looked at a fresh-water shell, but I should have said that the shell was Cyclas cornea. (402/1. It was Cyclas cornea.) Is Sphaenium corneum a synonym of Cyclas? Perhaps you could tell by looking to Mr. G. Jeffreys' book. If so, may we venture to call it so, or shall I put an (?) to the name?

As soon as I hear from you I will send my letter to "Nature." Do you take in "Nature," or shall I send you a copy?

CHAPTER 2.VIII. — MAN

I. Descent of Man. — II. Sexual Selection. — III. Expression of the Emotions.

2. VIII.I. DESCENT OF MAN, 1860-1882.

LETTER 403. TO C. LYELL. Down, April 27th {1860}.

I cannot explain why, but to me it would be an infinite satisfaction to believe that mankind will progress to such a pitch that we should {look} back at {ourselves} as mere Barbarians. I have received proof-sheets (with a wonderfully nice letter) of very hostile review by Andrew Murray, read before the Royal Society of Edinburgh. (403/1. "On Mr. Darwin's Theory of the Origin of Species," by Andrew Murray. "Proc. Roy. Soc., Edinb." Volume IV., pages 274-91, 1862. The review concludes with the following sentence: "I have come to be of opinion that Mr. Darwin's theory is unsound, and that I am to be spared any collision between my inclination and my convictions" (referring to the writer's belief in Design).) But I am tired with answering it. Indeed I have done nothing the whole day but answer letters.

LETTER 404. TO L. HORNER.

(404/1. The following letter occurs in the "Memoir of Leonard Horner, edited by his daughter Katherine M. Lyell," Volume II., page 300 (privately printed, 1890).)

Down, March 20th {1861}.

I am very much obliged for your Address (404/2. Mr. Horner's Anniversary Address to the Geological Society ("Proc. Geol. Soc." XVII., 1861).) which has interested me much...I thought that I had read up pretty well on the antiquity of man; but you bring all the facts so well together in a condensed focus, that the case seems much clearer to me. How curious about the Bible! (404/3. At page lxviii. Mr. Horner points out that the "chronology, given in the margin of our Bibles," i.e., the statement that the world was created 4004 B.C., is the work of Archbishop Usher, and is in no way binding on those who believe in the inspiration of Scripture. Mr. Horner goes on (page lxx): "The retention of the marginal note in question is by no means a matter of indifference; it is untrue, and therefore it is mischievous." It is interesting that Archbishop Sumner and Dr. Dawes, Dean of Hereford, wrote with approbation of Mr. Horner's views on Man. The Archbishop says: "I have always considered the first verse of Genesis as indicating, rather than denying, a PREADAMITE world" ("Memoir of Leonard Horner, II.", page 303).) I declare I had fancied that the date was somehow in the Bible. You are coming out in a new light as a Biblical critic. I must thank you for some remarks on the "Origin of Species" (404/4. Mr. Horner (page xxxix) begins by disclaiming the qualifications of a competent critic, and confines himself to general remarks on the philosophic candour and freedom from dogmatism of the "Origin": he does, however, give an opinion on the geological chapters IX. and X. As a general criticism he quotes Mr. Huxley's article in the "Westminster Review," which may now be read in "Collected Essays," II., page 22.) (though I suppose it is almost as incorrect to do so as to thank a judge for a favourable verdict): what you have said has pleased me extremely. I am the more pleased, as I would rather have been well attacked than have been handled in the namby-pamby, old-woman style of the cautious Oxford Professor. (404/5. This no doubt refers to Professor Phillips' "Life on the Earth," 1860, a book founded on the author's "Rede Lecture," given before the University of Cambridge. Reference to this work will be found in "Life and Letters," II., pages 309, 358, 373.)

LETTER 405. TO J.D. HOOKER.

(405/1. Mr. Wallace was, we believe, the first to treat the evolution of Man in any detail from the point of view of Natural Selection, namely, in a paper in the "Anthropological Review and Journal of the Anthropological Society," May 1864, page clviii. The deep interest with which Mr. Darwin read his copy is graphically recorded in the continuous series of pencil-marks along the margins of the pages. His views are fully given in Letter 406. The phrase, "in this case it is too far," refers to Mr. Wallace's habit of speaking of the theory of Natural Selection as due entirely to Darwin.)

May 22nd 1864.

I have now read Wallace's paper on Man, and think it MOST striking and original and forcible. I wish he had written Lyell's chapters on Man. (405/2. See "Life and Letters," III., page 11 et seq. for Darwin's disappointment over Lyell's treatment of the evolutionary question in his "Antiquity of Man"; see also page 29 for Lyell's almost pathetic words about his own position between the discarded faith of many years and the new one not yet assimilated. See also Letters 132, 164, 170.) I quite agree about his high-mindedness, and have long thought so; but in this case it is too far, and I shall tell him so. I am not sure that I fully agree with his views about Man, but there is no doubt, in my opinion, on the remarkable genius shown by the paper. I agree, however, to the main new leading idea.

LETTER 406. TO A.R. WALLACE.

(406/1. This letter was published in "Life and Letters," III., page 89.)

Down, {May} 28th {1864}.

I am so much better that I have just finished a paper for the Linnean Society (406/2. On the three forms, etc., of Lythrum.); but I am not yet at all strong, I felt much disinclination to write, and therefore you must forgive me for not having sooner thanked you for your paper on Man (406/3. "Anthropological Review," May 1864.) received on the 11th. (406/4. Mr. Wallace wrote, May 10th, 1864: "I send you now my little contribution to the theory of the origin of man. I hope you will be able to agree with me. If you are able {to write} I shall be glad to have your criticisms. I was led to the subject by the necessity of explaining the vast mental and cranial differences between man and the apes combined with such small structural differences in other parts of the body, — and also by an endeavour to account for the diversity of human races combined with man's almost perfect stability of form during all historical epochs." But first let me say that I have hardly ever in my life been more struck by any paper than that on "Variation," etc., etc., in the "Reader." (406/5. "Reader," April 16th, 1864, an abstract of Mr. Wallace: "On the Phenomena of Variation and Geographical Distribution as illustrated by the Papilionidae of the Malayan Region." "Linn. Soc. Trans." XXV.) I feel sure that such papers will do more for the spreading of our views on the modification of species than any separate treatises on the simple subject itself. It is really admirable; but you ought not in the Man paper to speak of the theory as mine; it is just as much yours as mine. One correspondent has already noticed to me your "high-minded" conduct on this head.

But now for your Man paper, about which I should like to write more than I can. The great leading idea is quite new to me — viz. that during late ages the mind will have been modified more than the body; yet I had got as far as to see with you, that the struggle between the races of man depended entirely on intellectual and moral qualities. The latter part of the paper I can designate only as grand and most eloquently done. I have shown your paper to two or three persons who have been here, and they have been equally struck with it. I am not sure that I go with you on all minor points: when reading Sir G. Grey's account of the constant battles of Australian savages, I remember thinking that Natural Selection would come in, and likewise with the Esquimaux, with whom the art of fishing and managing canoes is said to be hereditary. I rather differ on the rank, under a classificatory point of view, which you assign to man; I do not think any character simply in excess ought ever to be used for the higher divisions. Ants would not be separated from other hymenopterous insects, however high the instinct of the one, and however low the instincts of the other. With respect to the differences of race, a conjecture has occurred to me that much may be due to the correlation of complexion (and consequently hair) with constitution. Assume that a dusky individual best escaped miasma, and you will readily see what I mean. I persuaded the Director-General of the Medical Department of the Army to send printed forms to the surgeons of all regiments in tropical countries to ascertain this point, but I daresay I shall never get any returns. Secondly, I suspect that a sort of sexual selection has been the most powerful means of changing the races of man. I can show that the different races have a widely different standard of beauty. Among savages the most powerful men will have the pick of the women, and they will generally leave the most descendants. I have collected a few notes on man, but I do not suppose I shall ever use them. Do you intend to follow out your views? and if so, would you like at some future time to have my few references and notes? I am sure I hardly know whether they are of any value, and they are at present in a state of chaos.