533 



THE POPULAR SCIENCE MONTHLY.— SUPPLEMENT. 



credible. And when, further, we remember that 

 those which did not so vary would also, accord- 

 ing to all the evidence, find mates and leave off- 

 spring, the actual result seems quite impossible 

 of attainment by such means. 



Without pretending to solve completely so 

 difficult a problem, I would point out a circum- 

 stance which seems to afford a clew. It is, that 

 the most highly-colored and most richly-varied 

 markings occur on those parts of the plumage 

 which have undergone the greatest modification, 

 or have acquired the most abnormal develop- 

 ment. In the peacock the tail-coverts are enor- 

 mously developed, and the " eyes " are situated 

 on the greatly-dilated ends. In the birds-of-para- 

 dise, breast, or neck, or head, or tail feathers are 

 greatly developed and highly colored. The hac- 

 kles of the cock and the scaly breasts of hum- 

 ming-birds are similar developments; while in 

 the Argus-pheasant the secondary quills are so 

 enormously lengthened and broadened as to have 

 become almost useless for flight. Now, it is 

 easily conceivable that, during this process of 

 development, inequalities in the distribution of 

 color may have arisen in different parts of the 

 same feather, and that spots and bands may thus 

 have become broadened out into shaded spots or 

 ocelli, in the way indicated by Mr. Darwin, much 

 as the spots and rings on a soap-bubble increase 

 with increasing tenuity. This is the more prob- 

 able, as in domestic fowls varieties tend to be- 

 come symmetrical, quite independently of sexual 

 selection. — (" Descent of Man," p. 424.) 



If, now, we accept the evidence of Mr. Dar- 

 win's most trustworthy correspondents that the 

 choice of the female, so far as she exerts any, 

 falls upon the " most vigorous, defiant, and met- 

 tlesome male," and if we further believe, what is 

 certainly the case, that these are, as a rule, the 

 most brightly colored and adorned with the finest 

 developments of plumage, we have a real and not 

 an hypothetical cause at work. For these most 

 healthy, vigorous, and beautiful males will have 

 the choice of the finest and most healthy females, 

 will have the most numerous and healthy families, 

 and will be able best to protect and rear those 

 families. Natural selection, and what may be 

 termed male selection, will tend to give them the 

 advantage in the struggle for existence, and thus 

 the fullest plumage and the finest colors will be 

 transmitted, and tend to advance in each succeed- 

 ing generation. 



There remains, however, what Mr. Darwin 

 evidently considers his strongest argument — the 

 display by the male of each species of its peculiar 



beauties of plumage and color. We have here, 

 no doubt, a very remarkable and very interesting 

 fact ; but this, too, may be explained by general 

 principles, quite independent of any choice or 

 volition of the female bird. During pairing-time 

 the male bird is in a state of great excitement, 

 and full of exuberant energy. Even unorna- 

 mented birds flutter their wings or spread them 

 out, erect their tails or crests, and thus give vent 

 to the nervous excitability w r ith which they are 

 overcharged. It is not improbable that crests 

 and other erectile feathers may be primarily of 

 use in frightening away enemies, since they are 

 generally erected when angry or during combat. 

 Those individuals who were most pugnacious and 

 defiant, and who brought these erectile plumes 

 most frequently and most powerfully into action, 

 would tend to increase them by use, and to 

 leave them further developed in some of their 

 descendants. If, in the course of this de- 

 velopment, color appeared, we have every 

 reason to believe it would be most -vivid 

 in these most pugnacious and energetic indi- 

 viduals, and as these would always have the 

 advantage in the rivalry for mates (to which ad- 

 vantage the excess of color and plumage might 

 sometimes conduce), there seems nothing to pre- 

 vent a progressive development of these orna- 

 ments in all dominant racts, that is, wherever 

 there was such a surplus of vitality, and such 

 complete adaptation to conditions, that the in- 

 convenience or danger produced by them was so 

 comparatively small as not to affect the superior- 

 ity of the race over its nearest allies. If, then, 

 those portions of the plumage which were origi- 

 nally erected and displayed became developed and 

 colored, the actual display, under the influence of 

 jealousy or sexual excitement, becomes intelligi- 

 ble. The males, in their rivalry with each other, 

 would see what plumes were most effective, and 

 each woidd endeavor to excel his enemy as far as 

 voluntary exertion could offset it, just as they en- 

 deavor to rival each other in song, even some- 

 times to the point of causing their own destruc- 

 tion. 



There is also a general argument against Mr. 

 Darwin's views on this question, founded on the 

 nature and potency of "natural" as opposed to 

 " sexual " selection, which appears to me to be 

 itself almost conclusive of the whole matter at 

 issue. Natural selection, or the survival of the 

 fittest, acts perpetually and on an enormous scale. 

 Taking the offspring of each pair of birds as, on 

 the average, only six annually, one-third of these 

 at most will be preserved, while the two-thirds 



