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TEE POPULAR SCIENCE MONTHLY.— SUPPLEMENT. 



thus each one finds a fresh mate ; and it leads to 

 the conclusion that permanently-unpaired birds 

 are very scarce ; so that, speaking broadly, every 

 bird finds a mate and breeds. But this would 

 almost or quite neutralize any effect of sexual 

 selection of color or ornament, since the less 

 highly-colored birds would be at no disadvantage 

 as regards leaving healthy offspring. If, how- 

 ever, heightened color is correlated with health 

 and vigor, and these healthy and vigorous birds 

 provide best for their young, and leave offspring 

 which, being equally healthy and vigorous, can 

 best provide for themselves, then natural selec- 

 tion becomes a preserver and intensifier of color. 

 Another most important consideration is, that 

 male butterflies rival or even excel the most gor- 

 geous male birds in bright colors and elegant 

 patterns ; and among these there is literally not 

 one particle of evidence that the female is in- 

 fluenced by color, or even that she has any power 

 of choice, while there is much direct evidence to 

 the contrary (" Descent of Man," page 318). The 

 weakness of the evidence for sexual selection 

 among these insects is so palpable that Mr. Dar- 

 win is obliged to supplement it by the singularly 

 inconclusive argument that " unless the females 

 prefer one male to another, the pairing must be 

 left to mere chance, and this does not appear 

 probable" (loc. cil., page 317). But he has just 

 said, "The males sometimes fight together in 

 rivalry, and many may be seen pursuing or 

 crowding round the same female ; " while in the 

 case of the silk-moths, "the females appear not 

 to evince the least choice in regard to their part- 

 ners." Surely, the plain inference from all this 

 is, that males fight and struggle for the almost 

 passive female, and that the most vigorous and 

 energetic, the strongest-winged or the most per- 

 severing, wins her. How can there be chance 

 in this ? Natural selection would here act, as in 

 birds, in perpetuating the strongest and most 

 vigorous males, and as these would usually be 

 the more highly-colored of their race, the same 

 results would be produced as regards the intensi- 

 fication and variation of color in the one case as 

 in the other. 



Let us now see how these principles will ap- 

 ply to some of the cases adduced by Mr. Darwin 

 in support of his theory of voluntary sexual se- 

 lection. 



In "Descent of Man," second edition, pp. 30*7 

 -316, we find an elaborate account of the various 

 modes of coloring of butterflies and moths, prov- 

 ing that the colored parts are always more or less 

 displayed, and that they have some evident rela- 



tion to an observer. Mr. Darwin then says: 

 " From the several foregoing facts it is impossi- 

 ble to admit that the brilliant colors of butter- 

 flies, and of some few moths, have commonly 

 been acquired for the sake of protection. We 

 have seen that their colors and elegant patterns 

 are arranged and exhibited as if for display. 

 Hence I am led to believe that the females prefer 

 or are most excited by the more brilliant males ; 

 for on any other supposition the males would, as 

 far as we can see, be ornamented to no purpose" 

 {loc. cit., p. 316). I am not aware that any one has 

 ever maintained that the brilliant colors of but- 

 terflies have " commonly been acquired for the 

 sake of protection," yet Mr. Darwin has himself 

 referred to cases in which the brilliant color is 

 so placed as to serve for protection ; as, for ex- 

 ample, the eye-spots on the hind-wings of moths, 

 which are pierced by birds, and so save the vital 

 parts of the insect, while the bright patch on the 

 orange-tip butterflies, which Mr. Darwin denies 

 are protective, may serve the same purpose. It 

 is, in fact, somewhat remarkable how very gen- 

 erally the black spots, ocelli, or bright patches 

 of color, are on the tips, margins, or disks of the 

 wings ; and, as the insects are necessarily visible 

 while flying, and this is the time when they are 

 most subject to attacks by insectivorous birds, 

 the position of the more conspicuous parts at 

 some distance from the body may be a real pro- 

 tection to them. Again, Mr. Darwin admits that 

 the white color of the male ghost-moth may ren- 

 der it more easily seen by the female while flying 

 about in the dusk, and if to this we add that it 

 will be also more readily distinguished from al- 

 lied species, we have a reason for diverse orna- 

 mentation in these insects quite sufficient to ac- 

 count for most of the facts, without believing in 

 the selection of brilliant males by the females, for 

 which there is not a particle of evidence. The 

 facts given to show that butterflies and other in- 

 sects can distinguish colors and are attracted by 

 colors similar to their own, are quite consistent 

 with the view that color, which continually tends 

 to appear, is utilized for purposes of identifica- 

 tion and distinction, when not required to be 

 modified or suppressed for purposes of protec- 

 tion. The cases of the females of some species 

 of Thecla, Callidryas, Colias, and Hipparchia^ 

 which have more conspicuous markings than the 

 male, may be due to several causes : to obtain 

 greater distinction from other species, for pro- 

 tection from birds, as in the case of the yellow- 

 under-wing moths, while sometimes — as in Hip- 

 parchia— the lower intensity of coloring in the 



