124 SEXUAL SELECTION: BIRDS. [Part II. 



the inside of the mouth of this Buceros is "black in the 

 male and flesh-colored in the female ; and their external 

 appearance of beauty would not be thus affected. I ob- 

 served in Chili 43 that the iris in the condor, when about a 

 year old, is dark-brown, but changes at maturity into yel- 

 lowish-brown in the male, and into bright red in the female. 

 The male has also a small, longitudinal, leaden-colored, 

 fleshy crest or comb. With many gallinaceous birds the 

 comb is highly ornamental, and assumes vivid colors dur- 

 ing the act of courtship ; but what are we to think of the 

 dull-colored comb of the condor, which does not appear to 

 us in the least ornamental ? The same question may be 

 asked in regard to various other characters, such as the 

 knob on the base of the beak of the Chinese goose (Anser 

 cygnoides), which is much larger in the male than in the fe- 

 male. No certain answer can be given to these questions ; 

 but we ought to be cautious in assuming that knobs and 

 various fleshy appendages cannot be attractive to the fe- 

 male, when we remember that with savage races of man 

 various hideous deformities — deep scars on the face with 

 the flesh raised into protuberances, the septum of the nose 

 pierced by sticks or bones, holes in the ears and lips 

 stretched widely open — are all admired as ornamental. 



Whether or not unimportant differences between the 

 sexes, such as those just specified, have been preserved 

 through sexual selection, these differences, as well as all 

 others, must primarily depend on the laws of variation. 

 On the principle of correlated development, the plumage 

 often varies on different parts of the body, or ove* the 

 whole body, in the same manner. We see this well illus- 

 trated in certain breeds of the fowl. In all the breeds the 

 feathers on the neck and loins of the males are elongated, 

 and are called hackles ; now when both sexes acquire a 

 top-knot, which is a new character in the genus, the feath- 



43 ' Zoology of + he Voyage of H. M. S. Beagle,' 1841, p. 6. 





