Volume Ii Part 10 (1/2)

If s.e.xes have been differentiated entirely by s.e.xual selection the females can have no relation to environment. But in groups when both s.e.xes require protection during feeding or repose, as snipes, woodc.o.c.k, ptarmigan, desert birds and animals, green forest birds, etc., arctic birds of prey, and animals, then both s.e.xes are modified for protection.

Why should that power entirely cease to act when s.e.xual differentiation exists and when the female requires protection, and why should the colour of so many FEMALE BIRDS seem to be protective, if it has not been made protective by selection.

It is contrary to the principles of ”Origin of Species,” that colour should have been produced in both s.e.xes by s.e.xual selection and never have been modified to bring the female into harmony with the environment. ”s.e.xual selection is less rigorous than Natural Selection,”

and will therefore be subordinate to it.

I think the case of female Pieris pyrrha proves that females alone can be greatly modified for protection. (450/1. My latest views on this subject, with many new facts and arguments, will be found in the later editions of my ”Darwinism,” Chapter X. (A.R.W.))

LETTER 451. A.R. WALLACE TO CHARLES DARWIN.

(451/1. On October 4th, 1868, Mr. Wallace wrote again on the same subject without adding anything of importance to his arguments of September 27th. We give his final remarks:--)

October 4th, 1868.

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 ”s.e.xual Selection” as a separate book as soon as possible; and then, while you are going on with your other work, there will no doubt be found some one to battle with me over your facts on this hard problem.

LETTER 452. TO A.R. WALLACE. Down, October 6th [1868].

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. Hamburg) in which both s.e.xes differ much from each other and from both s.e.xes of Gallus bankiva; and both s.e.xes are kept constant by selection. The comb of the Spanish male has been ordered to be upright, and that of Spanish female to lop over, and this has been effected. There are sub-breeds of game fowl, with females very distinct and males almost identical; but this, apparently, is the result of spontaneous variation, without special selection. I am very glad to hear of case of female Birds of Paradise.

I have never in the least doubted possibility of modifying female birds alone for protection, and I have long believed it for b.u.t.terflies. I have wanted only evidence for the female alone of birds having had their colour modified for protection. But then I believe that the variations by which a female bird or b.u.t.terfly could get or has got protective colouring have probably from the first been variations limited in their transmission to the female s.e.x. And so with the variations of the male: when the male is more beautiful than the female, I believe the variations were s.e.xually limited in their transmission to the males.

LETTER 453. TO B.D. WALSH. Down, October 31st, 1868.

(453/1. A short account of the Periodical Cicada (C. septendecim) is given by Dr. Sharp in the Cambridge Natural History, Insects II., page 570. We are indebted to Dr. Sharp for calling our attention to Mr. C.L.

Marlatt's full account of the insect in ”Bulletin No. 14 [NS.] of the U.S. Department of Agriculture,” 1898. The Cicada lives for long periods underground as larva and pupa, so that swarms of the adults of one race (septendecim) appear at intervals of 17 years, while those of the southern form or race (tredecim) appear at intervals of 13 years.

This fact was first made out by Phares in 1845, but was overlooked or forgotten, and was only re-discovered by Walsh and Riley in 1868, who published a joint paper in the ”American Entomologist,” Volume I., page 63. Walsh appears to have adhered to the view that the 13- and 17-year forms are distinct species, though, as we gather from Marlatt's paper (page 14), he published a letter to Mr. Darwin in which he speaks of the 13-year form as an incipient species; see ”Index to Missouri Entomolog.

Reports Bull. 6,” U.S.E.C., page 58 (as given by Marlatt). With regard to the cause of the difference in period of the two forms, Marlatt (pages 15, 16) refers doubtfully to difference of temperature as the determining factor. Experiments have been inst.i.tuted by moving 17-year eggs to the south, and vice versa with 13-year eggs. The results were, however, not known at the time of publication of Marlatt's paper.)

I am very much obliged for the extracts about the ”drumming,” which will be of real use to me.

I do not at all know what to think of your extraordinary case of the Cicadas. Professor Asa Gray and Dr. Hooker were staying here, and I told them of the facts. They thought that the 13-year and the 17-year forms ought not to be ranked as distinct species, unless other differences besides the period of development could be discovered. They thought the mere rarity of variability in such a point was not sufficient, and I think I concur with them. The fact of both the forms presenting the same case of dimorphism is very curious. I have long wished that some one would dissect the forms of the male stag-beetle with smaller mandibles, and see if they were well developed, i.e., whether there was an abundance of spermatozoa; and the same observations ought, I think, to be made on the rarer form of your Cicada. Could you not get some observer, such as Dr. Hartman (453/2. Mr. Walsh sent Mr. Darwin an extract from Dr. Hartman's ”Journal of the doings of a Cicada septendecim,” in which the females are described as flocking round the drumming males. ”Descent of Man” (1901), page 433.), to note whether the females flocked in equal numbers to the ”drumming” of the rarer form as to the common form? You have a very curious and perplexing subject of investigation, and I wish you success in your work.

LETTER 454. TO A.R. WALLACE. Down, June 15th [1869?].

You must not suppose from my delay that I have not been much interested by your long letter. I write now merely to thank you, and just to say that probably you are right on all the points you touch on, except, as I think, about s.e.xual selection, which I will not give up. My belief in it, however, is contingent on my general belief in s.e.xual selection. It is an awful stretcher to believe that a peac.o.c.k's tail was thus formed; but, believing it, I believe in the same principle somewhat modified applied to man.

LETTER 455. TO G.H.K. THWAITES. Down, February 13th [N.D.]

I wrote a little time ago asking you an odd question about elephants, and now I am going to ask you an odder. I hope that you will not think me an intolerable bore. It is most improbable that you could get me an answer, but I ask on mere chance. Macacus silenus (455/1. Macacus silenus L., an Indian ape.) has a great mane of hair round neck, and pa.s.sing into large whiskers and beard. Now what I want most especially to know is whether these monkeys, when they fight in confinement (and I have seen it stated that they are sometimes kept in confinement), are protected from bites by this mane and beard. Any one who watched them fighting would, I think, be able to judge on this head. My object is to find out with various animals how far the mane is of any use, or a mere ornament. Is the male Macacus silenus furnished with longer hair than the female about the neck and face? As I said, it is a hundred or a thousand to one against your finding out any one who has kept these monkeys in confinement.

LETTER 456. TO F. MULLER. Down, August 28th [1870].

I have to thank you very sincerely for two letters: one of April 25th, containing a very curious account of the structure and morphology of Bonatea. I feel that it is quite a sin that your letters should not all be published! but, in truth, I have no spare strength to undertake any extra work, which, though slight, would follow from seeing your letters in English through the press--not but that you write almost as clearly as any Englishman. This same letter also contained some seeds for Mr.