THE PROBLEM OF THE ORIGIN OF SPECIES. 



15 



arising de novo, as chance variations, and the gradual extension of like spots in two 

 rows of feathers. The one or more original spots, according to the general theory, 

 would first appear as minute rudiments, and then be gradually enlarged and intensi- 

 fied by the aid of natural selection, guided by their utility as recognition marks. 



Such a mode of origin would presuppose a plain, uniform gray ancestor, without 

 any spots or bars in the wings, and would raise many puzzling questions that would 

 be beyond the reach of investigation. For example: Why two bars? Why at the 

 posterior end of the wing? Why do the spots taper backwards to a more or less 

 sharp point in the chequered variety, while presenting a nearly square form in 

 typical bars? Why should they have first extended upward, or downward, and in 

 two rather than any other number of rows of feathers? If two rows of feathers 

 were favored long enough to establish the bars for ornamental or other purposes, 

 what freak of natural selection could have then interposed to turn a long-favored, 

 definitely directed extension into a diffuse general extension, and thus to neutralize 

 completely the very effects it was invoked to explain? 



Natural selection could not be supposed to originate or to guide the first indiffer- 



Explanation of Plate 2 — Continued. 



Notice. — (1) Double spots on 5 feathers. The upper spot disappears from the proximal end most rapidly 

 on mesial or shaft side. Asymmetry on Nos. 14 and 13. 



(2) The lower spot follows the upper in losing ground on its proximal end, and mainly on mesial side, and thus 

 keeps up a certain sympathetic change of form. But as soon as the upper disappears the lower fills up again on its 

 near end and becomes nearly square. 



(3) The lower spot is most perfect on 5 feathers (Nos. 12 to 8), pales gradually from No. 9 downward, and loses 

 in size rapidly from No. 7 downward. 



(4) The upper feathers have highest development, as shown in double spots, but the lower spot is best developed 

 in the middle feathers — from No. 12 to No. 8. From No. 7 to No. 2 the spot wanes and disappears. 



Terminal increases downward; subterminal increases upward, 

 to this plate in Chapter IV. — Ed.) 



(A fuller textual reference 



