More Letters of Charles Darwin Volume Ii Part 7

LETTER 429. TO A.R. WALLACE. Down, April 29th [1867].

I have been greatly interested by your letter, but your view is not new to me. (429/1. We have not been able to find Mr. Wallace's letter to which this is a reply. It evidently refers to Mr. Wallace's belief in the paramount importance of protection in the evolution of colour. This is clear from the P.S. to the present letter and from the pa.s.sages in the "Origin" referred to. The first reference, Edition IV., page 240, is as follows: "We can sometimes plainly see the proximate cause of the transmission of ornaments to the males alone; for a pea-hen with the long tail of the male bird would be badly fitted to sit on her eggs, and a coal-black female capercailzie would be far more conspicuous on her nest, and more exposed to danger, than in her present modest attire."

The pa.s.sages in Edition I. (pages 89, 101) do not directly bear on the question of protection.) If you will look at page 240 of the fourth edition of the "Origin" you will find it very briefly given with two extreme examples of the peac.o.c.k and black grouse. A more general statement is given at page 101, or at page 89 of the first edition, for I have long entertained this view, though I have never had s.p.a.ce 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 on Man I intend to discuss the whole subject of s.e.xual 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 s.e.xual 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. (429/2. See a letter of February 26th, 1867, to Mr.

Wallace, "Life and Letters" III., page 94.) I have got one capital case (genus forgotten) of a [Australian] bird in which the female has long tail-plumes, and which consequently builds a different nest from all her allies. (429/3. Menura superba: see "Descent of Man" (1901), page 687.

Rhynchoea, mentioned a line or two lower down, is discussed in the "Descent," page 727. The female is more brightly coloured than the male, and has a convoluted trachea, elsewhere a masculine character. There seems some reason to suppose that "the male undertakes the duty of incubation.") With respect 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 Rhynchoea, 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 enquiries. 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.

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.

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 on the value and beauty of your generalisation (429/4.

See Letter 203, Volume I.), 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.

LETTER 430. TO A.R. WALLACE. Down, May 5th [1867].

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 s.e.xual 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 s.e.xual selection by showing that new characters often appear in one s.e.x and are transmitted to that s.e.x 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 arise in either s.e.x and be transmitted to both s.e.xes, 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 the 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 s.e.xual 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 Hackel (430/1.

See "Descent of Man" (1901) page 402.) has recently well shown that the transparency and absence of colour in the lower oceanic animals, belonging to the most different cla.s.ses, 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." (430/2. "Westminster Review,"

July, 1867.) Your paper on the s.e.xual colouring of birds will, I have no doubt, be very striking. Forgive me, if you can, for a touch of illiberality about your paper.

LETTER 431. TO A.R. WALLACE. March 19th, 1868.

(431/1. "The Variation of Animals and Plants" having been published on January 30th, 1868, Mr. Darwin notes in his diary that on February 4th he "Began on Man and s.e.xual Selection." He had already (in 1864 and 1867) corresponded with Mr. Wallace on these questions--see for instance the "Life and Letters," III., page 89; but, owing to various interruptions, serious work on the subject did not begin until 1869. The following quotations show the line of work undertaken early in 1868.

Mr. Wallace wrote (March 19th, 1868): "I am glad you have got good materials on s.e.xual 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 s.e.xUALLY selected. We seem to require a series of bold and abrupt variations. How can we imagine that an inch in the tail of the peac.o.c.k, or 1/4-inch in that of the Bird of Paradise, would be noticed and preferred by the female.")

In regard to s.e.xual 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. J. Jenner Weir, however, has given me some facts showing that birds apparently admire details of plumage.

LETTER 432. TO F. MULLER. March 28th [1868].

I am particularly obliged to you for your observations on the stridulation of the two s.e.xes of Lamellicorns. (432/1. We are unable to find any mention of F. Muller's observations on this point; but the reference is clearly to Darwin's observations on Necrophorus and Pelobius, in which the stridulating rasp was bigger in the males in the first individuals examined, but not so in succeeding specimens. "Descent of Man," Edition II., Volume I., page 382.) I begin to fear that I am completely in error owing to that common cause, viz. mistaking at first individual variability for s.e.xual difference.

I go on working at s.e.xual selection, and, though never idle, I am able to do so little work each day that I make very slow progress. I knew from Azara about the young of the tapir being striped, and about young deer being spotted (432/2. Fritz Muller's views are discussed in the "Descent of Man," Edition II., Volume II., page 305.); I have often reflected on this subject, and know not what to conclude about the loss of the stripes and spots. From the geographical distribution of the striped and unstriped species of Equus there seems to be something very mysterious about the loss of stripes; and I cannot persuade myself that the common a.s.s has lost its stripes owing to being rendered more conspicuous from having stripes and thus exposed to danger.

LETTER 433. TO J. JENNER WEIR.

(433/1. Mr. John Jenner Weir, to whom the following letters are addressed, is frequently quoted in the "Descent of Man" as having supplied Mr. Darwin with information on a variety of subjects.)

Down, February 27th [1868].

I must thank you for your paper on apterous lepidoptera (433/2.

Published by the West Kent Natural History, Microscopical and Photographic Society, Greenwich, 1867. Mr. Weir's paper seems chiefly to have interested Mr. Darwin as affording a good case of gradation in the degree of degradation of the wings in various species.), which has interested me exceedingly, and likewise for the very honourable mention which you make of my name. It is almost a pity that your paper was not published in some Journal in which it would have had a wider distribution. It contained much that was new to me. I think the part about the relation of the wings and spiracles and tracheae might have been made a little clearer. Incidentally, you have done me a good service by reminding me of the rudimentary spurs on the legs of the partridge, for I am now writing on what I have called s.e.xual selection.

I believe that I am not mistaken in thinking that you have attended much to birds in confinement, as well as to insects. If you could call to mind any facts bearing on this subject, with birds, insects, or any animals--such as the selection by a female of any particular male--or conversely of a particular female by a male, or on the rivalry between males, or on the allurement of the females by the males, or any such facts, I should be most grateful for the information, if you would have the kindness to communicate it.

P.S.--I may give as instance of [this] cla.s.s of facts, that Barrow a.s.serts that a male Emberiza (?) at the Cape has immensely long tail-feathers during the breeding season (433/3. Barrow describes the long tail feathers of Emberiza longicauda as enduring "but the season of love." "An Account of Travels into the Interior of Southern Africa": London, 1801, Volume I., page 244.); and that if these are cut off, he has no chance of getting a wife. I have always felt an intense wish to make a.n.a.logous trials, but have never had an opportunity, and it is not likely that you or any one would be willing to try so troublesome an experiment. Colouring or staining the fine red breast of a bullfinch with some innocuous matter into a dingy tint would be an a.n.a.logous case, and then putting him and ordinary males with a female. A friend promised, but failed, to try a converse experiment with white pigeons--viz., to stain their tails and wings with magenta or other colours, and then observe what effect such a prodigious alteration would have on their courts.h.i.+p. (433/4. See Letter 428.) It would be a fairer trial to cut off the eyes of the tail-feathers of male peac.o.c.ks; but who would sacrifice the beauty of their bird for a whole season to please a mere naturalist?

LETTER 434. TO J. JENNER WEIR. Down, February 29th [1868].

I have hardly ever received a note which has interested me more than your last; and this is no exaggeration. I had a few cases of birds perceiving slight changes in the dress of their owners, but your facts are of tenfold value. I shall certainly make use of them, and need not say how much obliged I should be for any others about which you feel confident.

Do you know of any birds besides some of the gallinaceae which are polygamous? Do you know of any birds besides pigeons, and, as it is said, the raven, which pair for their whole lives?

Many years ago I visited your brother, who showed me his pigeons and gave me some valuable information. Could you persuade him (but I fear he would think it high treason) to stain a male pigeon some brilliant colour, and observe whether it excited in the other pigeons, especially the females, admiration or contempt?

For the chance of your liking to have a copy and being able to find some parts which would interest you, I have directed Mr. Murray to send you my recent book on "Variation under Domestication."

P.S.--I have somewhere safe references to cases of magpies, of which one of a pair has been repeatedly (I think seven times) killed, and yet another mate was always immediately found. (434/1. On this subject see "Descent of Man," Edition I., Volume II., page 104, where Mr. Weir's observations were made use of. This statement is quoted from Jenner ("Phil. Trans." 1824) in the "Descent of Man" (1901), page 620.) A gamekeeper told me yesterday of a.n.a.logous case. This perplexes me much.

Are there many unmarried birds? I can hardly believe it. Or will one of a pair, of which the nest has been robbed, or which are barren, always desert his or her mate for a strange mate with the attraction of a nest, and in one instance with young birds in the nest? The gamekeeper said during breeding season he had never observed a single or unpaired partridge. How can the s.e.xes be so equally matched?

P.S. 2nd.--I fear you will find me a great bore, but I will be as reasonable as can be expected in plundering one so rich as you.

P.S. 3rd.--I have just received a letter from Dr. Wallace (434/2.

See "Descent of Man," Edition I., Volume I., pages 386-401, where Dr. Wallace's observations are quoted.), of Colchester, about the proportional numbers of the two s.e.xes in Bombyx; and in this note, apropos to an incidental remark of mine, he stoutly maintains that female lepidoptera never notice the colours or appearance of the male, but always receive the first male which comes; and this appears very probable. He says he has often seen fine females receive old battered and pale-tinted males. I shall have to admit this very great objection to s.e.xual selection in insects. His observations no doubt apply to English lepidoptera, in most of which the s.e.xes are alike. The brimstone or orange-tip would be good to observe in this respect, but it is hopelessly difficult. I think I have often seen several males following one female; and what decides which male shall succeed? How is this about several males; is it not so?

LETTER 435. TO J. JENNER WEIR. 6, Queen Anne Street, Cavendish Square, W. [March 6th, 1868].

I have come here for a few weeks, for a little change and rest. Just as I was leaving home I received your first note, and yesterday a second; and both are most interesting and valuable to me. That is a very curious observation about the goldfinch's beak (435/1. "Descent of Man,"

Edition I., Volume I., page 39. Mr. Weir is quoted as saying that the birdcatchers can distinguish the males of the goldfinch, Carduelis elegans, by their "slightly longer beaks."), but one would hardly like to trust it without measurement or comparison of the beaks of several male and female birds; for I do not understand that you yourself a.s.sert that the beak of the male is sensibly longer than that of the female. If you come across any acute birdcatchers (I do not mean to ask you to go after them), I wish you would ask what is their impression on the relative numbers of the s.e.xes of any birds which they habitually catch, and whether some years males are more numerous and some years females.

I see that I must trust to a.n.a.logy (an unsafe support) for s.e.xual selection in regard to colour in b.u.t.terflies. You speak of the brimstone b.u.t.terfly and genus Edusa (435/2. Colias Edusa.) (I forget what this is, and have no books here, unless it is Colias) not opening their wings.

In one of my notes to Mr. Stainton I asked him (but he could or did not answer) whether b.u.t.terflies such as the Fritillaries, with wings bright beneath and above, opened and shut their wings more than Vanessae, most of which, I think, are obscure on the under surface. That is a most curious observation about the red underwing moth and the robin (435/3.

"Descent of Man," Edition I., Volume I., page 395. Mr. Weir describes the pursuit of a red-underwing, Triphoena p.r.o.nuba, by a robin which was attracted by the bright colour of the moth, and constantly missed the insect by breaking pieces off the wing instead of seizing the body. Mr.

Wallace's facts are given on the same page.), and strongly supports a suggestion (which I thought hardly credible) of A.R. Wallace, viz. that the immense wings of some exotic lepidoptera served as a protection from difficulty of birds seizing them. I will probably quote your case.

No doubt Dr. Hooker collected the Kerguelen moth, for I remember he told me of the case when I suggested in the "Origin," the explanation of the coleoptera of Madeira being apterous; but he did not know what had become of the specimens.

I am quite delighted to hear that you are observing coloured birds (435/4. "Descent of Man," Edition I., Volume II., page 110.), though the probability, I suppose, will be that no sure result will be gained. I am accustomed with my numerous experiments with plants to be well satisfied if I get any good result in one case out of five.

You will not be able to read all my book--too much detail. Some of the chapters in the second volume are curious, I think. If any man wants to gain a good opinion of his fellow-men, he ought to do what I am doing, pester them with letters.

LETTER 436. TO J. JENNER WEIR. 4, Chester Place, Regent's Park, N.W., March 13th [1868].

You make a very great mistake when you speak of "the risk of your notes boring me." They are of the utmost value to me, and I am sure I shall never be tired of receiving them; but I must not be unreasonable. I shall give almost all the facts which you have mentioned in your two last notes, as well as in the previous ones; and my only difficulty will be not to give too much and weary my readers. Your last note is especially valuable about birds displaying the beautiful parts of their plumage. Audubon (436/1. In his "Ornithological Biography," 5 volumes, Edinburgh, 1831-49.) gives a good many facts about the antics of birds during courts.h.i.+p, but nothing nearly so much to the purpose as yours.

I shall never be able to resist giving the whole substance of your last note. It is quite a new light to me, except with the peac.o.c.k and Bird of Paradise. I must now look to turkey's wings; but I do not think that their wings are beautiful when opened during courts.h.i.+p. Its tail is finely banded. How about the drake and Gallus bankiva? I forget how their wings look when expanded. Your facts are all the more valuable as I now clearly see that for b.u.t.terflies I must trust to a.n.a.logy altogether in regard to s.e.xual selection. But I think I shall make out a strong case (as far as the rather deceitful guide of a.n.a.logy will serve) in the s.e.xes of b.u.t.terflies being alike or differing greatly--in moths which do not display the lower surface of their wings not having them gaudily coloured, etc., etc.--nocturnal moths, etc.--and in some male insects fighting for the females, and attracting them by music.

My discussion on s.e.xual selection will be a curious one--a mere dovetailing of information derived from you, Bates, Wallace, etc., etc., etc.