420 THE DESCENT OF MAN. 



of the female are gamboge-yellow; with many hornhills (Bu- 

 ceros), as I hear from Mr. Blyth * the males have Intense crimson 

 eyes, and those of the females are white. In the Buceros hicornis, 

 the hind margin of the casque and a stripe on the crest of the 

 beak are black In the male, but not so in the female. Are we to 

 suppose that these black marks and the crimson color of the eyes 

 have been preserved or augmented through sexual selection in 

 the males? This is very doubtful; for Mr. Bartlett showed me in 

 the Zoological Gardens that the inside of the mouth of this 

 Buceros is black in the male and flesh-colored in the female; and 

 their external appearance or beauty would not be thus affected. 

 I observed in Chili" that the iris in the condor, when about a 

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

 brown in the male, and into bright red in the female. The male 

 has also a small, longitudinal, leaden-colored, fleshy crest or 

 comb. The comb of many gallinaceous birds is highly ornament- 

 al, and assumes vivid colors during 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 

 female. 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 female, 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 over the whole body. In the same manner. We see this 

 well illustrated 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 feathers on the head 

 of the male become hackle-shaped, evidently on the principle of 

 correlation; whilst those on the head of the female are of the 

 ordinary shape. The color also of the hackles forming the top- 

 knot of the male, is often correlated with that of the hackles on 

 the neck and loins, as may be seen by comparing these feathers 



*' See, also, Jerdon, 'Birds of India,' vol. 1. pp. 243-245. 

 " 'Zoology of the Voyage of H. M. S. Beagle,' 1841, p. 6. 



