THE COLORS OF ANIMALS AND PLANTS. 



539 



which are least fitted will die. At intervals of a 

 few years, whenever unfavorable conditions oc- 

 cur, five-sixths, nine-tenths, or even a greater pro- 

 portion of the whole yearly production are weed- 

 ed out, leaving only the most perfect and best 

 adapted to survive. Now, unless these survivors 

 are on the whole the most ornamental, this rigid 

 selective power must neutralize and destroy any 

 influence that may be exerted by female selection. 

 For the utmost that can be claimed for this is, 

 that a small fraction of the least ornamented do 

 not obtain mates, while a few of the most orna- 

 mented may leave move than the average number 

 of offspring. Unless, therefore, there is the strict- 

 est correlation between ornament and general per- 

 fection, the former can have no permanent ad- 

 vantage ; and if there is (as I maintain) such a 

 correlation, then the sexual selection of ornament 

 for which there is little or no evidence becomes 

 needless, because natural selection, which is an 

 admitted vera causa, will itself produce all the re- 

 sults. In the case of butterflies the argument be- 

 comes even stronger, because the fertility is so 

 much greater, and the weeding out of the unfit 

 takes place, to a great extent, in the egg and larva 

 state. Unless the eggs and larvse which escaped 

 to produce the next generation were those which 

 would produce the more highly-colored butter- 

 flies, it is difficult to perceive how the slight pre- 

 ponderance of color sometimes selected by the 

 females should not be wholly neutralized by the 

 extremely rigid selection for other qualities to 

 which the offspring in every stage are exposed. 

 The only way in which we can account for the 

 observed facts is, by the supposition that color 

 and ornament are strictly correlated with health, 

 vigor, and general fitness to survive. We have 

 shown that there is reason to believe that this is 

 the case, and, if so, voluntary sexual selection be- 

 comes as unnecessary as it would certainly be in- 

 effective. 



There is one other very curious case of sexual 

 coloring among birds — that, namely, in which the 

 female is decidedly brighter or more strongly 

 marked than the male ; as in the fighting quails 

 (Tttrnix), painted snipe (Rhynchcea), two species 

 of phalarope (Phalaropits), and the common cas- 

 sowary (Casuarius galeatus). In all these cases, 

 it is known that the males take charge of and in- 

 cubate the eggs, while the females are almost al- 

 ways larger and more pugnacious. In my " The- 

 ory of Birds' Nests " (" Natural Selection," page 

 251), I imputed this difference of color to the great- 

 er need for protection by the male bird while incu- 

 bating, to which Mr. Darwin has objected that the 



difference is not sufficient, and is not always so 

 distributed as to be most effective for this pur- 

 pose, and he believes that it is due to reversed 

 sexual selection, that is, to the female taking the 

 usual role of the male, and being chosen for her 

 brighter tints. We have already seen reason for 

 rejecting this latter theory in every case, and I 

 also admit that my theory of protection is, in this 

 case, only partially if at all applicable. But the 

 general theory of intensity of color being due to 

 general vital energy is quite applicable ; and the 

 fact that the superiority of the female in this re- 

 spect is quite exceptional, and is therefore proba- 

 bly not of very ancient date in any one case, will 

 account for the difference of color thus produced 

 being always comparatively slight. 



Theory of Typical Colors. — The remaining 

 kinds of animal colors — those which can neither 

 be classed as protective, warning, nor sexual — are 

 for the most part readily explained on the general 

 principles of the development of color which we 

 have now laid down. It is a most suggestive fact 

 that, in cases where color is required only as a 

 warning, as among the uneatable caterpillars, we 

 find, not one or two glaring tints only, but every 

 kind of color disposed in elegant patterns, and 

 exhibiting almost as much variety and beauty as 

 among insects and birds. Yet here, not only is 

 sexual selection out of the question, but the need 

 for recognition and identification by others of the 

 same species seems equally unnecessary. We can 

 then only impute this variety to the normal produc- 

 tion of color in organic forms, when fully exposed 

 to light and air and undergoing great and rapid 

 developmental modification. Among more per- 

 fect animals, where the need for recognition has 

 been added, we find intensity and variety of color 

 at its highest pitch among the South American 

 butterflies of the families Heliconidre and Danai- 

 dae, as well as among the Nymphalida? and Eryci- 

 nida3, many of which obtain the necessary protec- 

 tion in other ways. Among birds also, wherever 

 the habits are such that no special protection is 

 needed for the females, and where the species 

 frequent the depths of tropical forests and are 

 thus naturally protected from the swoop of birds 

 of prey, we find almost equally intense colora- 

 tion ; as in the trogons, barbets, and gapers. 



Of the mode of action of the general prin- 

 ciples of color-development among animals, we 

 have an excellent example in the humming-birds. 

 Of all birds these are at once the smallest, the 

 most active, and the fullest of vital energy. When 

 poised in the air, their wings are invisible, owing 



