Volume 1 / Part 2 — II.—The Complete Extant Correspondence between Wallace and Darwin (continued 2)
Reading edition
[pg 180]
The reason of my being so much interested just at present about sexual selection is that I have almost resolved to publish a little essay on the Origin of Mankind, and I still strongly think (though I failed to convince you, and this to me is the heaviest blow possible) that sexual selection has been the main agent in forming the races of man.
By the way, there is another subject which I shall introduce in my essay, viz. expression of countenance. Now, do you happen to know by any odd chance a very good-natured and acute observer in the Malay Archipelago who, you think, would make a few easy observations for me on the expression of the Malays when excited by various emotions. For in this case I would send to such person a list of queries.—I thank you for your most interesting letters, and remain yours very sincerely,
CH. DARWIN.
9 St. Mark's Crescent, N.W. March 11, 1867.
Dear Darwin,—I return your queries, but cannot answer them with any certainty. For the Malays I should say Yes to 1, 3, 8, 9, 10 and 17, and No to 12, 13 and 16; but I cannot be certain in any one. But do you think these things are of much importance? I am inclined to think that if you could get good direct observations you would find some of them often differ from tribe to tribe, from island to island, and sometimes from village to village. Some no doubt may be deep-seated, and would imply organic differences; but can you tell beforehand which these are? I presume the Frenchman shrugs his shoulders whether he is of the Norman, Breton, or Gaulish stock. Would it not be a good thing to send your List of Queries to some of the Bombay and Calcutta papers? as there must be numbers of Indian judges and other officers who would be interested and would send you hosts of replies. The [pg 181]Australian papers and New Zealand might also publish them, and then you would have a fine basis to go on.
Is your essay on Variation in Man to be a supplement to your volume on Domesticated Animals and Cultivated Plants? I would rather see your second volume on "The Struggle for Existence, etc.," for I doubt if we have a sufficiency of fair and accurate facts to do anything with man. Huxley, I believe, is at work upon it.
I have been reading Murray's volume on the Geographical Distribution of Mammals. He has some good ideas here and there, but is quite unable to understand Natural Selection, and makes a most absurd mess of his criticism of your views on oceanic islands.
By the bye, what an interesting volume the whole of your materials on that subject would, I am sure, make.—Yours very sincerely,
ALFRED R. WALLACE.
Down, Bromley, Kent, S.E. March, 1867.
My dear Wallace,—I thank you much for your two notes. The case of Julia Pastrana58 is a splendid addition to my other cases of correlated teeth and hair, and I will add it in correcting the proof of my present volume. Pray let me hear in course of the summer if you get any evidence about the gaudy caterpillars. I should much like to give (or quote if published) this idea of yours, if in any way supported, as suggested by you. It will, however, be a long time hence, for I can see that sexual selection is growing into quite a large subject, which I shall introduce into my essay on Man, supposing that I ever publish it.
I had intended giving a chapter on Man, inasmuch as many call him (not quite truly) an eminently domesticated animal; but I found the subject too large for a chapter. [pg 182]Nor shall I be capable of treating the subject well, and my sole reason for taking it up is that I am pretty well convinced that sexual selection has played an important part in the formation of races, and sexual selection has always been a subject which has interested me much.
I have been very glad to see your impression from memory on the expressions of Malays. I fully agree with you that the subject is in no way an important one: it is simply a "hobby-horse" with me about twenty-seven years old; and after thinking that I would write an essay on Man, it flashed on me that I could work in some "supplemental remarks on expression." After the horrid, tedious, dull work of my present huge and, I fear, unreadable book, I thought I would amuse myself with my hobby-horse. The subject is, I think, more curious and more amenable to scientific treatment than you seem willing to allow. I want, anyhow, to upset Sir C. Bell's view, given in his most interesting work, "The Anatomy of Expression," that certain muscles have been given to man solely that he may reveal to other men his feelings. I want to try and show how expressions have arisen.
That is a good suggestion about newspapers; but my experience tells me that private applications are generally most fruitful. I will, however, see if I can get the queries inserted in some Indian paper. I do not know names or addresses of any other papers.
I have just ordered, but not yet received, Murray's book: Lindley used to call him a blunder-headed man. It is very doubtful whether I shall ever have strength to publish the latter part of my materials.
My two female amanuenses are busy with friends, and I fear this scrawl will give you much trouble to read.—With many thanks, yours very sincerely,
CH. DARWIN.
[pg 183]
Down, Bromley, Kent, S.E. April 29, 1867.
Dear Wallace,—I have been greatly interested by your letter;59 but your view is not new to me. If you will look at p. 240 of the fourth edition of the "Origin," you will find it very briefly given with two extremes of the peacock and black grouse. A more general statement is given at p. 101, or at p. 89 of the first edition, for I have long entertained this view, though I have never had space to develop it. But I had not sufficient knowledge to generalise as far as you do about colouring and nesting. In your paper, perhaps you will just allude to my scanty remark in the fourth edition, because in my essay upon Man I intend to discuss the whole subject of sexual selection, explaining, as I believe it does, much with respect to man. I have collected all my old notes and partly written my discussion, and it would be flat work for me to give the leading idea as exclusively from you. But as I am sure from your greater knowledge of ornithology and entomology that you will write a much better discussion than I could, your paper will be of great use to me. Nevertheless, I must discuss the subject fully in my essay on Man. When we met at the Zoological Society and I asked you about the sexual differences in kingfishers, I had this subject in view; as I had when I suggested to Bates the difficulty about gaudy caterpillars which you have so admirably (as I believe it will prove) explained. I have got one capital case (genus forgotten) of an [Australian] bird in which the female has long-tailed plumes and which consequently builds a different nest from all her allies.60 With respect [pg 184]to certain female birds being more brightly coloured than the males, and the latter incubating, I have gone a little into the subject and cannot say that I am fully satisfied. I remember mentioning to you the case of Rhynchæa, but its nesting seems unknown. In some other cases the difference in brightness seemed to me hardly sufficiently accounted for by the principle of protection. At the Falkland Islands there is a carrion hawk in which the female (as I ascertained by dissection) is the brightest coloured, and I doubt whether protection will here apply; but I wrote several months ago to the Falklands to make inquiries. The conclusion to which I have been leaning is that in some of these abnormal cases the colour happened to vary in the female alone, and was transmitted to females alone, and that her variations have been selected through the admiration of the male.
It is a very interesting subject, but I shall not be able to go on with it for the next five or six months, as I am fully employed in correcting dull proof-sheets; when I return to the work I shall find it much better done by you than I could have succeeded in doing.
With many thanks for your very interesting note, believe me, dear Wallace, yours very sincerely,
CH. DARWIN.
It is curious how we hit on the same ideas. I have endeavoured to show in my MS. discussion that nearly the same principles account for young birds not being gaily coloured in many cases—but this is too complex a point for a note.
[pg 185]
Postscript. Down. April 29.
My dear Wallace,—On reading over your letter again, and on further reflection, I do not think (as far as I remember my words) that I expressed myself nearly strongly enough as to the value and beauty of your generalisation, viz. that all birds in which the female is conspicuously or brightly coloured build in holes or under domes. I thought that this was the explanation in many, perhaps most cases, but do not think I should ever have extended my view to your generalisation. Forgive me troubling you with this P.S.—Yours,
CH. DARWIN.
Down, Bromley, Kent, S.E. May 5, 1867.
My dear Wallace,—The offer of your valuable notes is most generous, but it would vex me to take so much from you, as it is certain that you could work up the subject very much better than I could. Therefore I earnestly and without any reservation hope that you will proceed with your paper, so that I return your notes.
You seem already to have well investigated the subject. I confess on receiving your note that I felt rather flat at my recent work being almost thrown away, but I did not intend to show this feeling. As a proof how little advance I had made on the subject, I may mention that though I had been collecting facts on the colouring and other sexual differences in mammals, your explanation with respect to the females had not occurred to me. I am surprised at my own stupidity, but I have long recognised how much clearer and deeper your insight into matters is than mine.
I do not know how far you have attended to the laws of inheritance, so what follows may be obvious to you. I have begun my discussion on sexual selection by showing that new characters often appear in one sex and are [pg 186]transmitted to that sex alone, and that from some unknown cause such characters apparently appear oftener in the male than in the female. Secondly, characters may be developed and be confined to the male, and long afterwards be transferred to the female. Thirdly, characters may, again, arise in either sex and be transmitted to both sexes, either in an equal or unequal degree. In this latter case I have supposed that the survival of the fittest has come into play with female birds and kept the female dull-coloured. With respect to the absence of spurs in female gallinaceous birds, I presume that they would be in the way during incubation; at least, I have got the case of a German breed of fowls in which the hens were spurred, and were found to disturb and break their eggs much.
With respect to the females of deer not having horns, I presume it is to save the loss of organised matter.
In your note you speak of sexual selection and protection as sufficient to account for the colouring of all animals; but it seems to me doubtful how far this will come into play with some of the lower animals, such as sea anemones, some corals, etc. etc.
On the other hand, Haeckel has recently well shown that the transparency and absence of colour in the lower oceanic animals, belonging to the most different classes, may be well accounted for on the principle of protection.
Some time or other I should like much to know where your paper on the nests of birds has appeared, and I shall be extremely anxious to read your paper in the Westminster Review.
Your paper on the sexual colouring of birds will, I have no doubt, be very striking.
Forgive me, if you can, for a touch of illiberality about your paper, and believe me yours very sincerely,
CH. DARWIN.
[pg 187]
Down, Bromley, Kent, S.E. July 6, 1867.
My dear Wallace,—I am very much obliged for your article on Mimicry,61 the whole of which I have read with the greatest interest. You certainly have the art of putting your ideas with remarkable force and clearness; now that I am slaving over proof-sheets it makes me almost envious.
I have been particularly glad to read about the birds' nests, and I must procure the Intellectual Observer; but the point which I think struck me most was about its being of no use to the Heliconias to acquire in a slight degree a disagreeable taste. What a curious case is that about the coral snakes. The summary, and indeed the whole, is excellent, and I have enjoyed it much.—With many thanks, yours very sincerely,
CH. DARWIN.
9 St. Mark's Crescent, N.W. Wednesday, [August or September, 1867].
Dear Darwin,—I am very sorry I was out when you called yesterday. I had just gone to the Zoological Gardens, and I met Sir C. Lyell, who told me you were in town.
If you should have time to go to Bayswater, I think you would be pleased to see the collections which I have displayed there in the form of an exhibition (though the public will not go to see it).
If you can go, with any friends, I should like to meet you there if you can appoint a time.
I am glad to find you continue in tolerable health.—Believe me yours very faithfully,
ALFRED R. WALLACE.
What do you think of the Duke of Argyll's criticisms, [pg 188]and the more pretentious one in the last number of the North British Review?
I have written a little article answering them both, but I do not yet know where to get it published.—A.R.W.
76-1/2 Westbourne Grove, Bayswater, W. October 1, 1867.
Dear Darwin,—I am sorry I was not in town when your note came. I took a short trip to Scotland after the British Association Meeting, and went up Ben Lawers. It was very cold and wet, and I could not find a companion or I should have gone as far as Glen Roy.
My article on "Creation by Law," in reply to the Duke of Argyll and the North British reviewer, is in the present month's number of the Quarterly Journal of Science. I cannot send you a copy because they do not allow separate copies to be printed.
There is a nice illustration of the predicted Madagascar moth and Angræcum sesquipedale.
I shall be glad to know whether I have done it satisfactorily to you, and hope you will not be so very sparing of criticism as you usually are.
I hope you are getting on well with your great book. I hear a rumour that we are to have one vol. of it about Christmas.
I quite forget whether I told you that I have a little boy, now three months old, and have named him Herbert Spencer (having had a brother Herbert). I am now staying chiefly in the country, at Hurstpierpoint, but come up to town once a month at least. You may address simply, "Hurstpierpoint, Sussex."
Hoping your health is tolerable and that all your family are well, believe me, dear Darwin, yours very faithfully,
ALFRED R. WALLACE.
[pg 189]
Down, Bromley, Kent, S.E. October 12 and 13, 1867.
My dear Wallace,—I ordered the journal a long time ago, but by some oversight received it only yesterday and read it. You will think my praise not worth having from being so indiscriminate, but if I am to speak the truth, I must say I admire every word.
You have just touched on the points which I particularly wished to see noticed. I am glad you had the courage to take up Angræcum62 after the Duke's attack; for I believe the principle in this case may be widely applied. I like the figure, but I wish the artist had drawn a better sphinx.
With respect to beauty, your remarks on hideous objects and on flowers not being made beautiful except when of practical use to them strike me as very good.
On this one point of beauty, I can hardly think that the Duke was quite candid. I have used in the concluding paragraph of my present book precisely the same argument as you have, even bringing in the bulldog,63 with respect to variations not having been specially ordained. Your [pg 190]metaphor of the river64 is new to me, and admirable; but your other metaphor, in which you compare classification and complex machines, does not seem to me quite appropriate, though I cannot point out what seems deficient. The point which seems to me strong is that all naturalists admit that there is a natural classification, and it is this which descent explains. I wish you had insisted a little more against the North British65 reviewer assuming that each variation which appears is a strongly marked one; though by implication you have made this very, plain. Nothing in your whole article has struck me more than your view with respect to the limit of fleetness in the racehorse and other such cases; I shall try and quote you on this head in the proof of my concluding chapter. I quite missed this explanation, though in the case of wheat I hit upon something analogous. I am glad you praise the Duke's book, for I was much struck with it. The part about flight seemed to me at first very good, but as the wing is articulated by a ball-and-socket joint, I suspect the Duke would find it very difficult to give any reason against the belief that the wing strikes the air more or less obliquely. I have been very glad to see your article and the drawing of the butterfly in Science Gossip. By the way, I cannot but think that you push protection too [pg 191]far in some cases, as with the stripes on the tiger. I have also this morning read an excellent abstract in the Gardeners' Chronicle of your paper on nests;66 I was not by any means fully converted by your letter, but I think now I am so; and I hope it will be published somewhere in extenso. It strikes me as a capital generalisation, and appears to me even more original than it did at first.
I have had an excellent and cautious letter from Mr. Geach of Singapore with some valuable answers on expression, which I owe to you.
I heartily congratulate you on the birth of "Herbert Spencer," and may he deserve his name, but I hope he will copy his father's style and not his namesake's. Pray observe, though I fear I am a month too late, when tears are first secreted enough to overflow; and write down date.
I have finished Vol. I. of my book, and I hope the whole will be out by the end of November; if you have the patience to read it through, which is very doubtful, you will find, I think, a large accumulation of facts which will be of service to you in your future papers, and they could not be put to better use, for you certainly are a master in the noble art of reasoning.
Have you changed your house to Westbourne Grove?
Believe me, my dear Wallace, yours very sincerely,
CH. DARWIN.
This letter is so badly expressed that it is barely intelligible, but I am tired with proofs.
P.S.—Mr. Warington has lately read an excellent and spirited abstract of the "Origin" before the Victoria Institute, and as this is a most orthodox body he has gained [pg 192]the name of the devil's advocate. The discussion which followed during three consecutive meetings is very rich from the nonsense talked. If you would care to see the number I could lend it you.
I forgot to remark how capitally you turn the table on the Duke, when you make him create the Angræcum and moth by special creation.
Hurstpierpoint. October 22, 1867.
Dear Darwin,—I am very glad you approve of my article on "Creation by Law" as a whole.
The "machine metaphor" is not mine, but the North British reviewer's. I merely accept it and show that it is on our side and not against us, but I do not think it at all a good metaphor to be used as an argument either way. I did not half develop the argument on the limits of variation, being myself limited in space; but I feel satisfied that it is the true answer to the very common and very strong objection, that "variation has strict limits." The fallacy is the requiring variation in domesticity to go beyond the limits of the same variation under nature. It does do so sometimes, however, because the conditions of existence are so different. I do not think a case can be pointed out in which the limits of variation under domestication are not up to or beyond those already marked out in nature, only we generally get in the species an amount of change which in nature occurs only in the whole range of the genus or family.
The many cases, however, in which variation has gone far beyond nature and has not yet stopped are ignored. For instance, no wild pomaceous fruit is, I believe, so large as our apples, and no doubt they could be got much larger if flavour, etc., were entirely neglected.
I may perhaps push "protection" too far sometimes, for [pg 193]it is my hobby just now, but as the lion and the tiger are, I think, the only two non-arboreal cats, I think the tiger stripe agreeing so well with its usual habitat is at least a probable case.
I am rewriting my article on Birds' Nests for the new Natural History Review.
I cannot tell you about the first appearance of tears, but it is very early—the first week or two, I think. I can see the Victoria Institute Magazine at the London Library.
I shall read your book, every word. I hear from Sir C. Lyell that you come out with a grand new theory at the end, which even the cautious (!) Huxley is afraid of! Sir C. said he could think of nothing else since he read it. I long to see it.
My address is Hurstpierpoint during the winter, and, when in town, 76-1/2 Westbourne Grove.
I suppose you will now be going on with your book on Sexual Selection and Man, by way of relaxation! It is a glorious subject, but will require delicate handling,—Yours very faithfully,
ALFRED R. WALLACE.
10 Duchess Street, W. February 7, 1868.
Dear Darwin,—I have to thank you for signing the Memorial as to the East London Museum, and also for your kindness in sending me a copy of your great book, which I have only just received. I shall take it down in the country with me next week, and enjoy every line at my leisure.
Allow me also to congratulate you on the splendid position obtained by your second son at Cambridge.
You will perhaps be glad to hear that I have been for some time hammering away at my Travels, but I fear I shall make a mess of it. I shall leave most of the Natural [pg 194]History generalisation, etc., for another work, as if I wait to incorporate all, I may wait for years.—Hoping you are quite well, believe me yours very faithfully,
ALFRED R. WALLACE.
Down, Bromley, Kent, S.E. February 22, [1868?].
My dear Wallace,—I am hard at work on sexual selection and am driven half mad by the number of collateral points which require investigation, such as the relative numbers of the two sexes, and especially on polygamy. Can you aid me with respect to birds which have strongly marked secondary sexual characters, such as birds of paradise, humming-birds, the rupicola or rock-thrush, or any other such cases? Many gallinaceous birds certainly are polygamous. I suppose that birds may be known not to be polygamous if they are seen during the whole breeding season to associate in pairs, or if the male incubates, or aids in feeding the young. Will you have the kindness to turn this in your mind? but it is a shame to trouble you now that, as I am heartily glad to hear, you are at work on your Malayan Travels. I am fearfully puzzled how far to extend your protective views with respect to the females in various classes. The more I work, the more important sexual selection apparently comes out.
Can butterflies be polygamous?—i.e. will one male impregnate more than one female?
Forgive me troubling you, and I daresay I shall have to ask your forgiveness again, and believe me, my dear Wallace, yours most sincerely,
CH. DARWIN.
P.S.—Baker has had the kindness to set the Entomological Society discussing the relative numbers of the sexes in insects, and has brought out some very curious results. [pg 195] Is the orang polygamous? But I daresay I shall find that in your papers in (I think) the Annals and Magazine of Natural History.
The following group of letters deals with the causes of the sterility of hybrids (see note in "More Letters," p. 287). Darwin's final view is given in the "Origin," 6th edit., 1900, p. 384. He acknowledges that it would be advantageous to two incipient species if, by physiological isolation due to mutual sterility, they could be kept from blending; but he continues: "After mature reflection, it seems to me that this could not have been effected through Natural Selection." And finally he concludes (p. 386): "But it would be superfluous to discuss this question in detail; for with plants we have conclusive evidence that the sterility of crossed species must be due to some principle quite independent of Natural Selection. Both Gäartner and Kolreuter have proved that in genera including numerous species a series can be formed from species which, when crossed, yield fewer and fewer seeds, to species which never produce a single seed, but yet are affected by the pollen of certain other species, for the germen swells. It is here manifestly impossible to select the more sterile individuals, which have already ceased to yield seeds; so that this acme of sterility, when the germen alone is affected, cannot have been gained through selection; and from the laws governing the various grades of sterility being so uniform throughout the animal and vegetable kingdoms, we may infer that the cause, whatever it may be, is the same or nearly the same in all cases."
Wallace still adhered to his view (see "Darwinism," 1889, p. 174, also p. 292 of "More Letters," note 1, and Letter 211, p. 299). The discussion of 1868 began with a letter from Wallace, written towards the end of February, giving his opinion on the "Variation of Animals and Plants"; the discussion on the sterility of hybrids is at p. 185, Vol. II., 1st edit.
[pg 196]
(Second and third sheets of a letter from Wallace, apparently of February, 1868.)
I am in the second volume of your book, and I have been astonished at the immense number of interesting facts you have brought together. I read the chapter on Pangenesis first, for I could not wait. I can hardly tell you how much I admire it. It is a positive comfort to me to have any feasible explanation of a difficulty that has always been haunting me, and I shall never be able to give it up till a better one supplies its place, and that I think hardly possible. You have now fairly beaten Spencer on his own ground, for he really offered no solution of the difficulties of the problem. The incomprehensible minuteness and vast numbers of the physiological germs or atoms (Which themselves must be compounded of numbers of Spencer's physiological units) is the only difficulty, but that is only on a par with the difficulties in all conceptions of matter, space, motion, force, etc. As I understood Spencer, his physiological units were identical throughout each species, but slightly different in each different species; but no attempt was made to show how the identical form of the parent or ancestors came to be built up of such units.
The only parts I have yet met with where I somewhat differ from your views are in the chapter on the Causes of Variability, in which I think several of your arguments are unsound: but this is too long a subject to go into now.
Also, I do not see your objection to sterility between allied species having been aided by Natural Selection. It appears to me that, given a differentiation of a species into two forms, each of which was adapted to a special sphere of existence, every slight degree of sterility would be a positive advantage, not to the individuals who were sterile, [pg 197]but to each form. If you work it out, and suppose the two incipient species A, B to be divided into two groups, one of which contains those which are fertile when the two are crossed, the other being slightly sterile, you will find that the latter will certainly supplant the former in the struggle for existence, remembering that you have shown that in such a cross the offspring would be more vigorous than the pure breed, and would therefore certainly soon supplant them, and as these would not be so well adapted to any special sphere of existence as the pure species A and B, they would certainly in their turn give way to A and B.
I am sure all naturalists will be disgusted at the malicious and ignorant article in the Athenæum. It is a disgrace to the paper, and I hope someone will publicly express the general opinion of it. We can expect no good reviews of your book till the quarterlies or best monthlies come out.... I shall be anxious to see how Pangenesis is received.—Believe me yours very faithfully,
ALFRED R. WALLACE.
Down, Bromley, Kent, S.E. February 27, 1868.
My dear Wallace,—You cannot well imagine how much I have been pleased by what you say about Pangenesis. None of my friends will speak out, except, to a certain extent, Sir H. Holland,67 who found it very tough reading, but admits that some view "closely akin to it" will have to be admitted. Hooker, as far as I understand him, which I hardly do at present, seems to think that the hypothesis is little more than saying that organisms have such and such potentialities. What you say exactly and fully expresses my feeling, viz. that it is a relief to have some feasible explanation of the various facts, which can be given up as soon as any better hypothesis is found. It has [pg 198]certainly been an immense relief to my mind; for I have been stumbling over the subject for years, dimly seeing that some relation existed between the various classes of facts. I now hear from H. Spencer that his views quoted in my footnote refer to something quite distinct, as you seem to have perceived.
I shall be very glad to hear, at some future day, your criticisms on the causes of variability.
Indeed, I feel sure that I am right about sterility and Natural Selection. Two of my grown-up children who are acute reasoners have two or three times at intervals tried to prove me wrong, and when your letter came they had another try, but ended by coming back to my side. I do not quite understand your case, and we think that a word or two is misplaced. I wish some time you would consider the case under the following point of view. If sterility is caused or accumulated through Natural Selection, then, as every degree exists up to absolute barrenness, Natural Selection must have the power of increasing it. Now take two species, A and B, and assume that they are (by any means) half-sterile, i.e. produce half the full number of offspring. Now try and make (by Natural Selection) A and B absolutely sterile when crossed, and you will find how difficult it is. I grant, indeed it is certain, that the degree of sterility of the individuals of A and B will vary, but any such extra-sterile individuals of, we will say, A, if they should hereafter breed with other individuals of A, will bequeath no advantage to their progeny, by which these families will tend to increase in number over other families of A, which are not more sterile when crossed with B. But I do not know that I have made this any clearer than in the chapter in my book. It is a most difficult bit of reasoning, which I have gone over and over again on paper with diagrams. [pg 199]I shall be intensely curious to see your article in the Journal of Travel.
Many thanks for such answers as you could give. From what you say I should have inferred that birds of paradise were probably polygamous. But after all, perhaps it is not so important as I thought. I have been going through the whole animal kingdom in reference to sexual selection, and I have just got to the beginning of Lepidoptera, i.e. to end of insects, and shall then pass on to Vertebrata. But my ladies next week are going (ill-luck to it) to take me nolens-volens to London for a whole month.
I suspect Owen wrote the article in the Athenæum, but I have been told that it is Berthold Seeman. The writer despises and hates me.
Hearty thanks for your letter—you have indeed pleased me, for I had given up the great god Pan as a stillborn deity. I wish you could be induced to make it clear with your admirable powers of elucidation in one of the scientific journals.
I think we almost entirely agree about sexual selection, as I now follow you to large extent about protection to females, having always believed that colour was often transmitted to both sexes; but I do not go quite so far about protection.—Always yours most sincerely,
CH. DARWIN.
Hurstpierpoint. March 1, 1868.
My dear Darwin,—I beg to enclose what appears to me a demonstration, on your own principles, that Natural Selection could produce sterility of hybrids.
If it does not convince you I shall be glad if you will point out where the fallacy lies. I have taken the two cases of a slight sterility overcoming a perfect fertility, and of a perfect sterility overcoming a partial fertility—the beginning and end of the process. You admit that variations [pg 200]in fertility and sterility occur, and I think you will also admit that if I demonstrate that a considerable amount of sterility would be advantageous to a variety, that is sufficient proof that the slightest variation in that direction would be useful also, and would go on accumulating.
Sir C. Lyell spoke to me as if he greatly admired pangenesis. I am very glad H. Spencer at once acknowledges that his view was something quite distinct from yours. Although, as you know, I am a great admirer of his, I feel how completely his view failed to go to the root of the matter, as yours does. His explained nothing, though he was evidently struggling hard to find an explanation. Yours, as far as I can see, explains everything in growth and reproduction, though of course the mystery of life and consciousness remains as great as ever.
Parts of the chapter on Pangenesis I found hard reading, and have not quite mastered yet, and there are also throughout the discussions in Vol. II. many bits of hard reading on minute points which we, who have not worked experimentally at cultivation and crossing as you have done, can hardly see the importance of, or their bearing on the general question.
If I am asked, I may perhaps write an article on the book for some periodical, and if so shall do what I can to make pangenesis appreciated.
I suppose Mrs. Darwin thinks you must have a holiday, after the enormous labour of bringing out such a book as that. I am sorry I am not now staying in town. I shall, however, be up for two days on Thursday, and shall hope to see you at the Linnean, where Mr. Trimen has a paper on some of his wonderful South African mimetic butterflies.
I hope this will reach you before you leave.—Believe me yours very faithfully,
ALFRED R. WALLACE.
[pg 201]
Hurstpierpoint. March 8, 1868.
Dear Darwin,—I am very sorry your letter came back here while I was going to town, or I should have been very pleased to have seen you.
Trimen's paper at the Linnean was a very good one, but the only opponents were Andrew Murray and B. Seeman. The former talked utter nonsense about the "harmony of nature" produced by "polarisation," alike in "rocks, plants and animals," etc. etc. etc. And Seeman objected that there was mimicry among plants, and that our theory would not explain it.
Lubbock answered them both in his best manner.
Pray take your rest, and put my last notes by till you return to Down, or let your son discover the fallacies in them.
Would you like to see the specimens of pupæ of butterflies whose colours have changed in accordance with the colour of the surrounding objects? They are very curious, and Mr. T.W. Wood, who bred them, would, I am sure, be delighted to bring them to show you. His address is 89 Stanhope Street, Hampstead Road, N.W.—Believe me yours very faithfully,
ALFRED R. WALLACE.
Darwin had already written a short note to Wallace expressing a general dissent from his views.
4 Chester Place, Regent's Park, N.W. March 17, 1868.
My dear Wallace,—Many thanks about Pieridæ. I have no photographs up here, but will remember to send one from Down. Should you care to have a large one, of treble or quadruple common size, I will with pleasure send you one under glass cover, to any address you like in London, either now or hereafter. I grieve to say we shall not be here on April 2nd, as we return home on the 31st. In [pg 202]summer I hope that Mrs. Wallace and yourself will pay us a visit at Down, soon after you return to London; for I am sure you will allow me the freedom of an invalid.
My paper to-morrow at the Linnean Society is simply to prove, alas! that primrose and cowslip are as good species as any in the world, and that there is no trustworthy evidence of one producing the other. The only interesting point is the frequency of the production of natural hybrids, i.e. oxlips, and the existence of one kind of oxlip which constitutes a third good and distinct species. I do not suppose that I shall be able to attend the Linnean Society to-morrow.
I have been working hard in collecting facts on sexual selection every morning in London, and have done a good deal; but the subject grows more and more complex, and in many respects more difficult and doubtful. I have had grand success this morning in tracing gradational steps by which the peacock tail has been developed: I quite feel as if I had seen a long line of its progenitors.
I do not feel that I shall grapple with the sterility argument till my return home; I have tried once or twice and it has made my stomach feel as if it had been placed in a vice. Your paper has driven three of my children half-mad—one sat up to twelve o'clock over it. My second son, the mathematician, thinks that you have omitted one almost inevitable deduction which apparently would modify the result. He has written out what he thinks, but I have not tried fully to understand him. I suppose that you do not care enough about the subject to like to see what he has written?
I hope your book progresses.
I am intensely anxious to see your paper in Murray's Journal.—My dear Wallace, yours very sincerely,
CH. DARWIN.
[pg 203]
Hurstpierpoint. March 19, 1868.
Dear Darwin,—I should very much value a large photograph of you, and also a carte for my album, though it is too bad to ask you for both, as you must have so many applicants.
I am sorry I shall not see you in town, but shall look forward with pleasure to paying you a visit in the summer.
I am sorry about the Primulas, but I feel sure some such equally good case will some day be discovered, for it seems impossible to understand how all natural species whatever should have acquired sterility. Closely allied forms from adjacent islands would, I should think, offer the best chance of finding good species fertile inter se; since even if Natural Selection induces sterility I do not see how it could affect them, or why they should always be sterile, and varieties never.
I am glad you have got good materials on sexual selection. It is no doubt a difficult subject. One difficulty to me is, that I do not see how the constant minute variations, which are sufficient for Natural Selection to work with, could be sexually selected. We seem to require a series of bold and abrupt variations. How can we imagine that an inch in the tail of a peacock, or a quarter of an inch in that of the bird of paradise, would be noticed and preferred by the female?
Pray let me see what your son says about the sterility selection question. I am deeply interested in all that concerns the powers of Natural Selection, but, though I admit there are a few things it cannot do, I do not yet believe sterility to be one of them.
In case your son has turned his attention to mathematical physics, will you ask him to look at the enclosed question, [pg 204]which I have vainly attempted to get an answer to?—Believe me yours very faithfully,
ALFRED R. WALLACE.
4 Chester Place, Regent's Park, N.W. March 19-24, 1868.
My dear Wallace,—I have sent your query to Cambridge to my son. He ought to answer it, for he got his place of Second Wrangler chiefly by solving very difficult problems. I enclose his remarks on two of your paragraphs: I should like them returned some time, for I have not studied them, and let me have your impression.
I have told E. Edwards to send one of my large photographs to you addressed to 76-1/2 Westbourne Grove, not to be forwarded. When at home I will send my carte.
The sterility is a most [? puzzling] problem. I can see so far, but I am hardly willing to admit all your assumptions, and even if they were all admitted, the process is so complex and the sterility (as you remark in your note) so universal, even with species inhabiting quite distinct countries (as I remarked in my chapter), together with the frequency of a difference in reciprocal unions, that I cannot persuade myself that it has been gained by Natural Selection, any more than the difficulty of grafting distinct genera and the impossibility of grafting distinct families. You will allow, I suppose, that the capacity of grafting has not been directly acquired through Natural Selection.
I think that you will be pleased with the second volume or part of Lyell's Principles, just out.
In regard to sexual selection. A girl sees a handsome man, and without observing whether his nose or whiskers are the tenth of an inch longer or shorter than in some other man, admires his appearance and says she will marry him. So, I suppose, with the pea-hen; and the tail has been increased in length merely by, on the whole, presenting a more gorgeous appearance. Jenner Weir, however, [pg 205]has given me some facts showing that birds apparently admire details of plumage.—Yours most sincerely,
C. DARWIN.
Hurstpierpoint. March 24, [1868?].
Dear Darwin,—Many thanks for the photo, which I shall get when I go to town.
I return your son's notes with my notes on them.
Without going into any details, is not this a strong general argument?—
1. A species varies occasionally in two directions, but owing to their free intercrossing they (the variations) never increase.
2. A change of conditions occurs which threatens the existence of the species, but the two varieties are adapted to the changing conditions, and, if accumulated, will form two new species adapted to the new conditions.
3. Free crossing, however, renders this impossible, and so the species is in danger of extinction.
4. If sterility could be induced, then the pure races would increase more rapidly and replace the old species.
5. It is admitted that partial sterility between varieties does occasionally occur. It is admitted the degree of this sterility varies. Is it not probable that Natural Selection can accumulate these variations and thus save the species?
If Natural Selection can not do this, how do species ever arise, except when a variety is isolated?
Closely allied species in distinct countries being sterile is no difficulty, for either they diverged from a common ancestor in contact, and Natural Selection increased the sterility, or they were isolated, and have varied since, in which case they have been for ages influenced by distinct conditions which may well produce sterility.
If the difficulty of grafting was as great as the difficulty [pg 206]of crossing, and as regular, I admit it would be a most serious objection. But it is not. I believe many distinct species can be grafted while others less distinct cannot. The regularity with which natural species are sterile together, even when very much alike, I think is an argument in favour of the sterility having been generally produced by Natural Selection for the good of the species.
The other difficulty, of unequal sterility of reciprocal crosses, seems none to me; for it is a step to more complete sterility, and as such would be useful and would be increased by selection.
I have read Sir C. Lyell's second volume with great pleasure. He is, as usual, very cautious, and hardly ever expresses a positive opinion, but the general effect of the whole book is very strong, as the argument is all on our side.
I am in hopes it will bring in a new set of converts to Natural Selection, and will at all events lead to a fresh ventilation of the subject.—Believe me yours very faithfully,
ALFRED R. WALLACE.
4 Chester Place, Regent's Park, N.W. March 27, 1868.
My dear Wallace,—My son has failed in your problem, and says that it is "excessively difficult": he says you will find something about it in Thomson and Tait, "Natural Philosophy" (art. 649). He has, however, sent the solution, if the plate rested on a square rim, but he supposes this will not answer your purpose; nevertheless, I have forwarded it by this same post. It seems that the rim being round makes the problem much more difficult.
I enclose my photograph, which I have received from Down. I sent your answer to George on his objection to your argument on sterility, but have not yet heard from him. I dread beginning to think over this fearful problem, [pg 207]which I believe beats the plate on the circular rim; but I will sometime. I foresee, however, that there are so many doubtful points that we shall never agree. As far as a glance serves it seems to me, perhaps falsely, that you sometimes argue that hybrids have an advantage from greater vigour, and sometimes a disadvantage from not being so well fitted to their conditions. Heaven protect my stomach whenever I attempt following your argument!—Yours most sincerely,
C. DARWIN.
Down, Bromley, Kent. April 6, 1868.
My dear Wallace,—I have been considering the terrible problem. Let me first say that no man could have more earnestly wished for the success of Natural Selection in regard to sterility than I did, and when I considered a general statement (as in your last note) I always felt sure it could be worked out, but always failed in detail, the cause being, as I believe, that Natural Selection cannot effect what is not good for the individual, including in this term a social community. It would take a volume to discuss all the points; and nothing is so humiliating to me as to agree with a man like you (or Hooker) on the premises and disagree about the result.
I agree with my son's argument and not with rejoinder. The cause of our difference, I think, is that I look at the number of offspring as an important element (all circumstances remaining the same) in keeping up the average number of individuals within any area. I do not believe that the amount of food by any means is the sole determining cause of number. Lessened fertility is equivalent to a new source of destruction. I believe if in one district a species produce from any cause fewer young, the deficiency would be supplied from surrounding districts. This applies to your par. 5. If the species produced fewer young [pg 208]from any cause in every district, it would become extinct unless its fertility were augmented through Natural Selection (see H. Spencer).
I demur to the probability and almost to the possibility of par. 1, as you start with two forms, within the same area, which are not mutually sterile, and which yet have supplanted the parent-form (par. 6). I know of no ghost of a fact supporting belief that disinclination to cross accompanies sterility. It cannot hold with plants, or the lower fixed aquatic animals. I saw clearly what an immense aid this would be, but gave it up. Disinclination to cross seems to have been independently acquired, probably by Natural Selection; and I do not see why it would not have sufficed to have prevented incipient species from blending to have simply increased sexual disinclination to cross.
Par. 11: I demur to a certain extent to amount of sterility and structural dissimilarity necessarily going together, except indirectly and by no means strictly. Look at the case of pigeons, fowls, and cabbages.
I overlooked the advantage of the half-sterility of reciprocal crosses; yet, perhaps from novelty, I do not feel inclined to admit the probability of Natural Selection having done its work so clearly.
I will not discuss the second case of utter sterility; but your assumptions in par. 13 seem to me much too complicated. I cannot believe so universal an attribute as utter sterility between remote species was acquired in so complex a manner. I do not agree with your rejoinder on grafting; I fully admit that it is not so closely restricted as crossing; but this does not seem to me to weaken the case as one of analogy. The incapacity of grafting is likewise an invariable attribute of plants sufficiently remote from each other, and sometimes of plants pretty closely allied.
The difficulty of increasing the sterility, through Natural [pg 209]Selection, of two already sterile species seems to me best brought home by considering an actual case. The cowslip and primrose are moderately sterile, yet occasionally produce hybrids: now these hybrids, two or three or a dozen in a whole parish, occupy ground which might have been occupied by either pure species, and no doubt the latter suffer to this small extent. But can you conceive that any individual plants of the primrose and cowslip, which happened to be mutually rather more sterile (i.e. which when crossed yielded a few less seeds) than usual, would profit to such a degree as to increase in number to the ultimate exclusion of the present primrose and cowslip? I cannot.
My son, I am sorry to say, cannot see the full force of your rejoinder in regard to the second head of continually augmented sterility. You speak in this rejoinder, and in par. 5, of all the individuals becoming in some slight degree sterile in certain districts; if you were to admit that by continued exposure to these same conditions the sterility would inevitably increase, there would be no need of Natural Selection. But I suspect that the sterility is not caused so much by any particular conditions, as by long habituation to conditions of any kind. To speak according to pangenesis, the gemmules of hybrids are not injured, for hybrids propagate freely by buds; but their reproductive organs are somehow affected, so that they cannot accumulate the proper gemmules, in nearly the same manner as the reproductive organs of a pure species become affected when exposed to unnatural conditions.
This is a very ill-expressed and ill-written letter. Do not answer it, unless the spirit urges you. Life is too short for so long a discussion. We shall, I greatly fear, never agree.—My dear Wallace, most sincerely yours,
CH. DARWIN.
[pg 210]
Hurstpierpoint. [?] April 8, 1868.
Dear Darwin,—I am sorry you should have given yourself the trouble to answer my ideas on Sterility. If you are not convinced, I have little doubt but that I am wrong; and in fact I was only half convinced by my own arguments, and I now think there is about an even chance that Natural Selection may or not be able to accumulate sterility. If my first proposition is modified to the existence of a species and a variety in the same area, it will do just as well for my argument. Such certainly do exist. They are fertile together, and yet each maintains itself tolerably distinct. How can this be, if there is no disinclination to crossing? My belief certainly is that number of offspring is not so important an element in keeping up population of a species as supply of food and other favourable conditions, because the numbers of a species constantly vary greatly in different parts of its area, whereas the average number of offspring is not a very variable element.
However, I will say no more but leave the problem as insoluble, only fearing that it will become a formidable weapon in the hands of the enemies of Natural Selection.
While writing a few pages on the northern alpine forms of plants on the Java mountains I wanted a few cases to refer to like Teneriffe, where there are no northern forms, and scarcely any alpine. I expected the volcanoes of Hawaii would be a good case, and asked Dr. Seeman about them. It seems a man has lately published a list of Hawaiian plants, and the mountains swarm with European alpine genera and some species!68 Is not this most extraordinary and a puzzler? They are, I believe, truly oceanic [pg 211]islands in the absence of mammals and the extreme poverty of birds and insects, and they are within the tropics. Will not that be a hard nut for you when you come to treat in detail on geographical distribution?
I enclose Seeman's note, which please return when you have copied the list, if of any use to you.
Many thanks for your carte, which I think very good. The large one had not arrived when I was in town last week.
Sir C. Lyell's chapter on Oceanic Islands I think very good.—Believe me, dear Darwin, yours very faithfully,
ALFRED R. WALLACE.
Down, Bromley, Kent, S.E. April 9, 1868.
My dear Wallace,—You allude in your note to several points which I should much enjoy discussing with you did time and strength permit. I know Dr. Seeman is a good botanist, but I most strongly advise you to show the list to Hooker before you make use of the materials in print. Hooker seems much overworked, and is now gone a tour, but I suppose you will be in town before very long, and could see him. The list is quite unintelligible to me; it is not pretended that the same species exist in the Sandwich Islands and Arctic regions; and as far as the genera are concerned, I know that in almost every one of them species inhabit such countries as Florida, North Africa, New Holland, etc. Therefore these, genera seem to me almost mundane, and their presence in the Sandwich Islands will not, as I suspect in my ignorance, show any relation to the Arctic regions. The Sandwich Islands, though I have never considered them much, have long been a sore perplexity to me: they are eminently oceanic in position and productions; they have long been separated from each other; and there are only slight signs [pg 212]of subsidence in the islets to the westward. I remember, however, speculating that there must have been some immigration during the glacial period from North America or Japan; but I cannot remember what my grounds were. Some of the plants, I think, show an affinity with Australia. I am very glad that you like Lyell's chapter on Oceanic Islands, for I thought it one of the best in the part which I have read. If you do not receive the big photo of me in due time, let me hear.—Yours very sincerely,
CH. DARWIN.
The following refers to Wallace's article, "A Theory of Birds' Nests," in Andrew Murray's Journal of Travel, i. 73. He here treats in fuller detail the view already published in the Westminster Review for July, 1867, p. 38. The rule which Wallace believes, with very few exceptions, to hold good is, "that when both sexes are of strikingly gay and conspicuous colours, the nest is ... such as to conceal the sitting bird; while, whenever there is a striking contrast of colours, the male being gay and conspicuous, the female dull and obscure, the nest is open and the sitting bird exposed to view." At this time Wallace allowed considerably more influence to sexual selection (in combination with the need of protection) than in his later writings. See his letter to Darwin of July 23, 1877 (p. 298), which fixes the period at which the change in his views occurred. He finally rejected Darwin's theory that colours "have been developed by the preference of the females, the more ornamented males becoming the parents of each successive generation." (See "Darwinism," 1889, p. 285.)
Down, Bromley, Kent, S.E. April 15, 1868.
My dear Wallace,—I have been deeply interested by your admirable article on Birds' Nests. I am delighted to see that we really differ very little—not more than two men almost always will. You do not lay much or any stress on new characters spontaneously appearing in one [pg 213]sex (generally the male) and being transmitted exclusively, or more commonly only in excess, to that sex. I, on the other hand, formerly paid far too little attention to protection. I had only a glimpse of the truth. But even now I do not go quite as far as you. I cannot avoid thinking rather more than you do about the exceptions in nesting to the rule, especially the partial exceptions, i.e. when there is some little difference between the sexes in species which build concealed nests. I am now quite satisfied about the incubating males; there is so little difference in conspicuousness between the sexes. I wish with all my heart I could go the whole length with you. You seem to think that such birds probably select the most beautiful females: I must feel some doubt on this head, for I can find no evidence of it. Though I am writing so carping a note, I admire the article thoroughly.
And now I want to ask a question. When female butterflies are more brilliant than their males, you believe that they have in most cases, or in all cases, been rendered brilliant so as to mimic some other species and thus escape danger. But can you account for the males not having been rendered equally brilliant and equally protected? Although it may be most for the welfare of the species that the female should be protected, yet it would be some advantage, certainly no disadvantage, for the unfortunate male to enjoy an equal immunity from danger. For my part, I should say that the female alone had happened to vary in the right manner, and that the beneficial variations had been transmitted to the same sex alone. Believing in this, I can see no improbability (but from analogy of domestic animals a strong probability): the variations leading to beauty must often have occurred in the males alone, and been transmitted to that sex alone. Thus I should account in many cases for the greater beauty of the male over the female, [pg 214]without the need of the protective principle. I should be grateful for an answer on this point.
I hope that your Eastern book progresses well.—My dear Wallace, yours sincerely,
C. DARWIN.
Sir Clifford Allbutt's view, referred to in the following letter, probably had reference to the fact that the sperm-cell goes, or is carried, to the germ-cell, never vice versa. In this letter Darwin gives the reason for the "law" referred to. Wallace has been good enough to supply the following note (May 27, 1902): "It was at this time that my paper on 'Protective Resemblance' first appeared in the Westminster Review, in which I adduced the greater, or, rather, the more continuous, importance of the female (in the lower animals) for the race, and my 'Theory of Birds' Nests' (Journal of Travel and Natural History, No. 2), in which I applied this to the usually dull colours of female butterflies and birds. It is to these articles, as well as to my letters, that Darwin chiefly refers."
Down, Bromley, Kent, S.E. April 30, 1868.
My dear Wallace,—Your letter, like so many previous ones, has interested me much. Dr. Allbutt's view occurred to me some time ago, and I have written a short discussion on it. It is, I think, a remarkable law, to which I have found no exception. The foundation lies in the fact that in many cases the eggs or seeds require nourishment and protection by the mother-form for some time after impregnation. Hence the spermatozoa and antherozoids travel in the lower aquatic animals and plants to the female, and pollen is borne to the female organ. As organisms rise in the scale it seems natural that the male should carry the spermatozoa to the females in his own body. As the male is the searcher he has received and gained more eager passions than the female; and, very differently from you, I look at this as one great difficulty [pg 215]in believing that the males select the more attractive females; as far as I can discover they are always ready to seize on any female, and sometimes on many females. Nothing would please me more than to find evidence of males selecting the more attractive females [? in pigeons69]: I have for months been trying to persuade myself of this. There is the case of man in favour of this belief, and I know in hybrid [lizards'70] unions of males preferring particular females, but alas! not guided by colour. Perhaps I may get more evidence as I wade through my twenty years' mass of notes.
I am not shaken about the female protected butterflies: I will grant (only for argument) that the life of the male is of very little value; I will grant that the males do not vary; yet why has not the protective beauty of the female been transferred by inheritance to the male? The beauty would be a gain to the male, as far as we can see, as a protection; and I cannot believe that it would be repulsive to the female as she became beautiful. But we shall never convince each other. I sometimes marvel how truth progresses, so difficult is it for one man to convince another unless his mind is vacant. Nevertheless, I myself to a certain extent contradict my own remark; for I believe far more in the importance of protection than I did before reading your articles.
I do not think you lay nearly stress enough in your articles on what you admit in your letter, viz. "there seems to be some production of vividness ... of colour in the male independent of protection." This I am making a chief point; and have come to your conclusion so far that I believe that intense colouring in the female sex is often checked by being dangerous.
That is an excellent remark of yours about no known [pg 216]case of the male alone assuming protective colours; but in the cases in which protection has been gained by dull colours, I presume that sexual selection would interfere with the male losing his beauty. If the male alone had acquired beauty as a protection, it would be most readily overlooked, as males are so often more beautiful than their females. Moreover, I grant that the loss of the male is somewhat less precious and thus there would be less rigorous selection with the male, so he would be less likely to be made beautiful through Natural Selection for protection. (This does not apply to sexual selection, for the greater the excess of males and the less precious their lives, so much the better for sexual selection.) But it seems to me a good argument, and very good if it could be thoroughly established.—Yours most sincerely,
C. DARWIN.
I do not know whether you will care to read this scrawl.
P.S.—I heard yesterday that my photograph had been sent to your London address—Westbourne Grove.
Down, Bromley, Kent, S.E. May 5, 1868.
My dear Wallace,—I am afraid I have caused you a great deal of trouble in writing to me at such length. I am glad to say that I agree almost entirely with your summary, except that I should put sexual selection as an equal or perhaps as even a more important agent in giving colour than natural selection for protection. As I get on in my work I hope to get clearer and more decided ideas. Working up from the bottom of the scale I have as yet only got to fishes. What I rather object to in your articles is that I do not think anyone would infer from them that you place sexual selection even as high as No. 4 in your summary. It was very natural that you should give only a [pg 217]line to sexual selection in the summary to the Westminster Review, but the result at first to my mind was that you attributed hardly anything to its power. In your penultimate note you say: "In the great mass of cases in which there is great differentiation of colour between the sexes, I believe it is due almost wholly to the need of protection to the female." Now, looking to the whole animal kingdom I can at present by no means admit this view; but pray do not suppose that because I differ to a certain extent, I do not thoroughly admire your several papers and your admirable generalisation on birds' nests. With respect to this latter point, however, although following you, I suspect that I shall ultimately look at the whole case from a rather different point of view.
You ask what I think about the gay-coloured females of Pieris:71 I believe I quite follow you in believing that the colours are wholly due to mimicry; and I further believe that the male is not brilliant from not having received through inheritance colour from the female, and from not himself having varied; in short, that he has not been influenced by Selection.
I can make no answer with respect to the elephants. With respect to the female reindeer, I have hitherto looked at the horns simply as the consequence of inheritance not having been limited by sex.
Your idea about colour being concentrated in the smaller males seems good, and I presume that you will not object to my giving it as your suggestion.—Believe me, my dear Wallace, with many thanks, yours very sincerely,
CH. DARWIN.
Wallace's more recent views on the question of Natural Selection and Sterility may be found in a note written by [pg 218]him in 1899: "When writing my 'Darwinism' and coming again to the consideration of the problem of the effect of Natural Selection in accumulating variations in the amount of sterility between varieties or incipient species, twenty years later, I became more convinced than I was when discussing with Darwin, of the substantial accuracy of my argument. Recently a correspondent who is both a naturalist and a mathematician has pointed out to me a slight error in my calculation at p, 183 (which does not, however, materially affect the result) disproving the physiological selection of the late Dr. Romanes, but he can see no fallacy in my argument as to the power of Natural Selection to increase sterility between incipient species, nor, so far as I am aware, has anyone shown such fallacy to exist.
"On the other points on which I differed from Mr. Darwin in the foregoing discussion—the effect of high fertility on population of a species, etc.—I still hold the views I then expressed, but it would be out of place to attempt to justify them here."—A.R.W.
9 St. Mark's Crescent, N.W. August 16, [1868?],
Dear Darwin,—I ought to have written before to thank you for the copies of your paper on "Primula" and on "Cross Unions of Dimorphic Plants, etc." The latter is particularly interesting, and the conclusion most important; but I think it makes the difficulty of how these forms, with their varying degrees of sterility, originated, greater than ever. If Natural Selection could not accumulate varying degrees of sterility for the plant's benefit, then how did sterility ever come to be associated with one cross of a trimorphic plant rather than another? The difficulty seems to be increased by the consideration that the advantage of a cross with a distinct individual is gained just as well by illegitimate as by legitimate unions. By what means, then, did illegitimate unions ever become sterile? It would seem a far simpler way for each plant's pollen [pg 219]to have acquired a prepotency on another individual's stigma over that of the same individual, without the extraordinary complication of three differences of structure and eighteen different unions with varying degrees of sterility!
However, the fact remains an excellent answer to the statement that sterility of hybrids proves the absolute distinctness of the parents.
I have been reading with great pleasure Mr. Bentham's last admirable address,72 in which he so well replies to the gross misstatements of the Athenæum; and also says a word in favour of pangenesis. I think we may now congratulate you on having made a valuable convert, whose opinions on the subject, coming so late and being evidently so well considered, will have much weight.
I am going to Norwich on Tuesday to hear Dr. Hooker, who I hope will boldly promulgate "Darwinianism" in his address. Shall we have the pleasure of seeing you there?
I am engaged in negotiations about my book.
Hoping you are well and getting on with your next volumes, believe me yours very faithfully,
ALFRED R. WALLACE.
Freshwater, Isle of Wight. August 19, 1868.
My dear Wallace,—Thanks for your note. I did sometimes think of going to Norwich, for I should have very much liked it, but it has been quite out of the question. We have been here for five weeks for a change, and it has done me some little good; but I have been forced to live the life of a drone, and for a month before leaving home I was unable to do anything and had to stop all work.
We return to Down to-morrow.
Hooker has been here for two or three days, so that I [pg 220]have had much talk about his Address. I am glad that you will be there.
It is real good news that your book is so advanced that you are negotiating about its publication.
With respect to dimorphic plants: it is a great puzzle, but I fancy I partially see my way—too long for a letter and too speculative for publication. The groundwork of the acquirement of such peculiar fertility (for what you say about any other distinct individual being, as it would appear, sufficient, is very true) rests on the stamens and pistil having varied first in relative length, as actually occurs irrespective of dimorphism, and the peculiar kind of fertility characteristic of dimorphic and the trimorphic plants having been secondarily acquired. Pangenesis makes very few converts: G.H. Lewes is one.
I had become, before my nine weeks' horrid interruption of all work, extremely interested in sexual selection and was making fair progress. In truth, it has vexed me much to find that the further I get on, the more I differ from you about the females being dull-coloured for protection. I can now hardly express myself as strongly even as in the "Origin." This has much decreased the pleasure of my work.
In the course of September, if I can get at all stronger, I hope to get Mr. J. Jenner Weir (who has been wonderfully kind in giving me information) to pay me a visit, and I will then write for the chance of your being able to come and, I hope, bring with you Mrs. Wallace. If I could get several of you together, it would be less dull for you, for of late I have found it impossible to talk with any human being for more than half an hour, except on extraordinarily good days.—Believe me, my dear Wallace, ever yours sincerely,
CH. DARWIN.
[pg 221]
9 St. Mark's Crescent. August 30, [1868?].
Dear Darwin,—I was very sorry to hear you had been so unwell again, and hope you will not exert yourself to write me such long letters. Darwinianism was in the ascendant at Norwich (I hope you do not dislike the word, for we really must use it), and I think it rather disgusted some of the parsons, joined with the amount of advice they received from Hooker and Huxley. The worst of it is that there are no opponents left who know anything of natural history, so that there are none of the good discussions we used to have. G.H. Lewes seems to me to be making a great mistake in the Fortnightly, advocating many distinct origins for different groups, and even, if I understand him, distinct origins for some allied groups, just as the anthropologists do who make the red man descend from the orang, the black man from the chimpanzee—or rather the Malay and orang one ancestor, the negro and chimpanzee another. Vogt told me that the Germans are all becoming converted by your last book.
I am certainly surprised that you should find so much evidence against protection having checked the acquirement of bright colour in females; but I console myself by presumptuously hoping that I can explain your facts, unless they are derived from the very groups on which I chiefly rest—birds and insects. There is nothing necessarily requiring protection in females; it is a matter of habits. There are groups in which both sexes require protection in an exactly equal degree, and others (I think) in which the male requires most protection, and I feel the greatest confidence that these will ultimately support my view, although I do not yet know the facts they may afford.
Hoping you are in better health, believe me, dear Darwin, yours faithfully,
ALFRED R. WALLACE.
[pg 222]
9 St. Mark's Crescent, N.W. September 5, [1868?].
Dear Darwin,—It will give me great pleasure to accept your kind invitation for next Saturday and Sunday, and my wife would very much like to come too, and will if possible. Unfortunately, there is a new servant coming that very day, and there is a baby at the mischievous age of a year and a quarter to be left in somebody's care; but I daresay it will be managed somehow.
I will drop a line on Friday to say if we are coming the time you mention.—Believe me yours very faithfully,
ALFRED R. WALLACE.
Friday.
My dear Darwin,—My wife has arranged to accompany me to-morrow, and we hope to be at Orpington Station at 5.44, as mentioned by you.—Very truly yours,
ALFRED R. WALLACE.
Down, Bromley, Kent, S.E. September 16, 1868.
My dear Wallace,—The beetles have arrived, and cordial thanks: I never saw such wonderful creatures in my life. I was thinking of something quite different. I shall wait till my son Frank returns, before soaking and examining them. I long to steal the box, but return it by this post, like a too honest man.
I am so much pleased about the male musk Callichroma; for by odd chance I told Frank a week ago that next spring he must collect at Cambridge lots of Cerambyx moschatus, for as sure as life he would find the odour sexual!
You will be pleased to hear that I am undergoing severe distress about protection and sexual selection: this morning I oscillated with joy towards you; this evening I have [pg 223]swung back to the old position, out of which I fear I shall never get.
I did most thoroughly enjoy my talk with you three gentlemen, and especially with you, and to my great surprise it has not knocked me up. Pray give my kindest remembrances to Mrs. Wallace, and if my wife were at home she would cordially join in this.—Yours very sincerely,
CH. DARWIN.
I have had this morning a capital letter from Walsh of Illinois; but details too long to give.
Among Wallace's papers was found the following draft of a letter of his to Darwin:
9 St. Mark's Crescent, N.W. September 18, 1868.
Dear Darwin,—The more I think of your views as to the colours of females, the more difficulty I find in accepting them, and as you are now working at the subject I hope it will not interrupt you to hear "counsel on the other side."
I have a "general" and a "special" argument to submit.
1. Female birds and insects are generally exposed to more danger than the male, and in the case of insects their existence is necessary for a longer period.
2. They therefore require in some way or other a special balance of protection.
3. Now, if the male and female were distinct species, with different habits and organisations, you would, I think, at once admit that a difference of colour serving to make that one less conspicuous which evidently required more protection than the other had been acquired by Natural Selection.
4. But you admit that variations appearing in one sex are transmitted (often) to that sex only: there is therefore [pg 224]nothing to prevent Natural Selection acting on the two sexes as if they were two species.
5. Your objection that the same protection would to a certain extent be useful to the male, seems to me utterly unsound, and directly opposed to your own doctrine so convincingly urged in the "Origin," "that Natural Selection never can improve an animal beyond its needs." So that admitting abundant variation of colour in the male, it is impossible that he can be brought by Natural Selection to resemble the female (unless her variations are always transmitted to him), because the difference of their colours is to balance the difference in their organisations and habits, and Natural Selection cannot give to the male more than is needed to effect that balance.
6. The fact that in almost all protected groups the females perfectly resemble the males shows, I think, a tendency to transference of colour from one sex to the other when this tendency is not injurious.
Or perhaps the protection is acquired because this tendency exists. I admit therefore in the case of concealed nests they [habits] may have been acquired for protection.
Now for the special case.
7. In the very weak-flying Leptalis both sexes mimic Heliconidæ.
8. In the much more powerful Papilio, Pieris, and Diadema it is generally the female only that mimics Danaida.
9. In these cases the females often acquire more bright and varied colours than the male. Sometimes, as in Pieris pyrrha, conspicuously so.
10. No single case is known of a male Papilio, Pieris, Diadema (or any other insect?) alone mimicking a Danais, etc. [pg 225] 11. But colour is more frequent in males, and variations always seem ready for purposes of sexual or other selection.
12. The fair inference seems to be that given in proposition 5 of the general argument, viz. that each species and each sex can only be modified by selection just as far as is absolutely necessary, not a step farther. A male, being by structure and habits less exposed to danger and less requiring protection than the female, cannot have more protection given to it by Natural Selection, but a female must have some extra protection to balance the greater danger, and she rapidly acquires it in one way or another.
13. An objection derived from cases like male fish, which seem to require protection, yet having brighter colours, seems to me of no more weight than is that of the existence of many white and unprotected species of Leptalis to Bates's theory of mimicry, that only one or two species of butterflies perfectly resemble leaves, or that the instincts or habits or colours that seem essential to the preservation of one animal are often totally absent in an allied species.
Down, Bromley, Kent. September 23, 1868.
My dear Wallace,—I am very much obliged for all your trouble in writing me your long letter, which I will keep by me and ponder over. To answer it would require at least 200 folio pages! If you could see how often I have rewritten some pages, you would know how anxious I am to arrive as near as I can to the truth. We differ, I think, chiefly from fixing our minds perhaps too closely on different points, on which we agree: I lay great stress on what I know takes place under domestication: I think we start with different fundamental notions on inheritance. I find [pg 226]it most difficult, but not, I think, impossible, to see how, for instance, a few red feathers appearing on the head of a male bird, and which are at first transmitted to both sexes, could come to be transmitted to males alone;73 but I have no difficulty in making the whole head red if the few red feathers in the male from the first tended to be sexually transmitted. I am quite willing to admit that the female may have been modified, either at the same time or subsequently, for protection, by the accumulation of variations limited in their transmission to the female sex. I owe to your writings the consideration of this latter point. But I cannot yet persuade myself that females alone have often been modified for protection. Should you grudge the trouble briefly to tell me whether you believe that the plainer head and less bright colours of [female symbol]74 chaffinch, the less red on the head and less clean colours of [female symbol] goldfinch, the much less red on breast of [female symbol] bullfinch, the paler crest of goldencrest wren, etc., have been acquired by them for protection? I cannot think so; any more than I can that the considerable differences between [female symbol] and [male symbol] house-sparrow, or much greater brightness of [male symbol] Parus cæruleus (both of which build under cover) than of [female symbol] Parus are related to protection. I even misdoubt much whether the less blackness of blackbird is for protection.
Again, can you give me reason for believing that the merest differences between female pheasants, the female Gallus bankiva, the female of black grouse, the pea-hen, female partridge, have all special reference to protection [pg 227]under slightly different conditions? I of course admit that they are all protected by dull colours, derived, as I think, from some dull-ground progenitor; and I account partly for their difference by partial transference of colour from the male, and by other means too long to specify; but I earnestly wish to see reason to believe that each is specially adapted for concealment to its environment.
I grieve to differ from you, and it actually terrifies me, and makes me constantly distrust myself.
I fear we shall never quite understand each other. I value the cases of bright-coloured, incubating male fishes—and brilliant female butterflies, solely as showing that one sex may be made brilliant without any necessary transference of beauty to the other sex; for in these cases I cannot suppose that beauty in the other sex was checked by selection.
I fear this letter will trouble you to read it. A very short answer about your belief in regard to the [female symbol] finches and Gallinaceæ would suffice.—Believe me, my dear Wallace, yours very sincerely,
CH. DARWIN.
9 St. Mark's Crescent, S.W. September 27, 1868.
Dear Darwin,—Your view seems to be that variations occurring in one sex are transmitted either to that sex exclusively or to both sexes equally, or more rarely partially transferred. But we have every gradation of sexual colours from total dissimilarity to perfect identity. If this is explained solely by the laws of inheritance, then the colours of one or other sex will be always (in relation to their environment) a matter of chance. I cannot think this. I think Selection more powerful than laws of inheritance, of which it makes use, as shown by cases of two, three or four forms of female butterflies, all of which have, I have little doubt, been specialised for protection. [pg 228] To answer your first question is most difficult, if not impossible, because we have no sufficient evidence in individual cases of slight sexual difference, to determine whether the male alone has acquired his superior brightness by sexual selection, or the female been made duller by need of protection, or whether the two causes have acted. Many of the sexual differences of existing species may be inherited differences from parent forms who existed under different conditions and had greater or less need of protection.
I think I admitted before the general tendency (probably) of males to acquire brighter tints. Yet this cannot be universal, for many female birds and quadrupeds have equally bright tints.
I think the case of [female symbol] Pieris pyrrha proves that females alone can be greatly modified for protection.
To your second question I can reply more decidedly. I do think the females of the Gallmaceæ you mention have been modified or been prevented from acquiring the brighter plumage of the male by need of protection. I know that the Gallus bankiva frequents drier and more open situations than the pea-hen of Java, which is found among grassy and leafy vegetation corresponding with the colours of the two. So the Argus pheasant, [male symbol] and [female symbol], are, I feel sure, protected by their tints corresponding to the dead leaves of the lofty forest in which they dwell, and the female of the gorgeous fire-back pheasant, Lophura viellottii, is of a very similar rich brown colour. I do not, however, at all think the question can be settled by individual cases, but only by large masses of facts.
The colours of the mass of female birds seem to me strictly analogous to the colours of both sexes of snipes, woodcocks, plovers, etc., which are undoubtedly protective.
Now, supposing, on your view, that the colours of a [pg 229]male bird become more and more brilliant by sexual selection, and a good deal of that colour is transmitted to the female till it becomes positively injurious to her during incubation and the race is in danger of extinction, do you not think that all the females who had acquired less of the male's bright colours or who themselves varied in a protective direction would be preserved, and that thus a good protective colouring would be acquired? If you admit that this could occur, and can show no good reason why it should not often occur, then we no longer differ, for this is the main point of my view.
Have you ever thought of the red wax-tips of the Bombycilla beautifully imitating the red fructification of lichens used in the nest, and therefore the females have it too? Yet this is a very sexual-looking character.
We begin printing this week.—Yours very faithfully,
ALFRED R. WALLACE.
P.S.—Pray don't distress yourself on this subject. It will all come right in the end, and after all it is only an episode in your great work.—A.R.W.
9 St. Mark's Crescent, N.W. October 4, 1868.
Dear Darwin,—I should have answered your letter before, but have been very busy reading over my MSS. the last time before going to press, drawing maps, etc. etc.
Your first question cannot be answered, because we have not, in individual cases of slight sexual difference, sufficient evidence to determine how much of that difference is due to sexual selection acting on the male, how much to natural selection (protective) acting on the female, or how much of the difference may be due to inherited differences from ancestors who lived under different conditions. On your second question I can give an opinion. I do think the [pg 230]females of the Gallinaceæ you mention have been either modified; or prevented from acquiring much of the brighter plumage of the males, by the need of protection. I know that Gallus bankiva frequents drier and more open situations than Pavo muticus, which in Java is found among grassy and leafy vegetation corresponding with the colours of the two females. So the Argus pheasants, male and female, are, I feel sure, protected by their tints corresponding to dead leaves of the dry lofty forests in which they dwell; and the female of the gorgeous fire-back pheasant, Lophura viellottii, is of a very similar rich brown colour.
These and many other colours of female birds seem to me exactly analogous to the colours of both sexes in such groups as the snipes, woodcocks, plovers, ptarmigan, desert birds, Arctic animals, greenbirds.
[The second page of this letter has been torn off. This letter and that of September 27 appear both to answer the same letter from Darwin. The last page of this or of another letter was placed with it in the portfolio of letters; it is now given.]
I am sorry to find that our difference of opinion on this point is a source of anxiety to you.
Pray do not let it be so. The truth will come out at last, and our difference may be the means of setting others to work who may set us both right.
After all, this question is only an episode (though an important one) in the great question of the origin of species, and whether you or I are right will not at all affect the main doctrine—that is one comfort.
I hope you will publish your treatise on Sexual Selection as a separate book as soon as possible, and then while you are going on with your other work, there will no [pg 231]doubt be found someone to battle with me over your facts, on this hard problem.
With best wishes and kind regards to Mrs. Darwin and all your family, believe me, dear Darwin, yours very faithfully,
ALFRED R. WALLACE.
Down, Bromley, Kent, S.E. October 6, 1868.
My dear Wallace,—Your letter is very valuable to me, and in every way very kind. I will not inflict a long answer, but only answer your queries. There are breeds (viz. Hamburgh) in which both sexes differ much from each other and from both sexes of G. bankiva; and both sexes are kept constant by selection.
The comb of Spanish [male symbol] has been ordered to be upright and that of Spanish [female symbol] to lop over, and this has been effected. There are sub-breeds of game fowl, with [female symbol]s very distinct and [male symbol]s almost identical; but this apparently is the result of spontaneous variation without special selection.
I am very glad to hear of the case of [female symbol] birds of paradise.
I have never in the least doubted the possibility of modifying female birds alone for protection; and I have long believed it for butterflies: I have wanted only evidence for the females alone of birds having had their colours modified for protection. But then I believe that the variations by which a female bird or butterfly could get or has got protective colouring have probably from the first been variations limited in their transmission to the female sex; and so with the variations of the male, where the male is more beautiful than the female, I believe the variations were sexually limited in their transmission to the males. I am delighted to hear that you have been hard at work on your MS.—Yours most sincerely,
CH. DARWIN.
[pg 232]
9 St. Mark's Crescent, N.W. January 20, 1869.
Dear Darwin,—It will give me very great pleasure if you will allow me to dedicate my little book of Malayan Travels to you, although it will be far too small and unpretending a work to be worthy of that honour. Still, I have done what I can to make it a vehicle for communicating a taste for the higher branches of Natural History, and I know that you will judge it only too favourably. We are in the middle of the second volume, and if the printers will get on, shall be out next month.
Have you seen in the last number of the Quarterly Journal of Science the excellent remarks on Fraser's article on Natural Selection failing as to Man? In one page it gets to the heart of the question, and I have written to the editor to ask who the author is.
My friend Spruce's paper on Palms is to be read to-morrow evening at the Linnean. He tells me it contains a discovery which he calls "alteration of function." He found a clump of Geonema all of which were females, and the next year the same clump were all males! He has found other facts analogous to this, and I have no doubt the subject is one that will interest you.
Hoping you are pretty well and are getting on steadily with your next volumes, and with kind regards to Mrs. Darwin and all your circle, believe me, dear Darwin, yours very faithfully,
ALFRED R. WALLACE.
P.S.—Have you seen the admirable article in the Guardian (!) on Lyell's "Principles"? It is most excellent and liberal. It is written by the Rev. Geo. Buckle, of Tiverton Vicarage, Bath, whom I met at Norwich and found a thoroughly scientific and liberal parson. Perhaps you have heard that I have undertaken to write an article for the Quarterly (!) on the same subject, to make [pg 233]up for that on "Modern Geology" last year not mentioning Sir C. Lyell.