Chap. VIII. 
SEXUAL SELECTION. 
295 
for the two sexes, though not quite alike, resemble each 
other more closely than do the sexes of the aboriginal 
parent-species, yet they acquire their characteristic 
plumage late in life, for the chickens are distinctly 
pencilled. Turning to other characters besides colour : 
the males alone of the wild parent-species and of most 
domestic breeds possess a fairly well developed comb, but 
in the young of the Spanish fowl it is largely developed 
at a very early age, and apparently in consequence of 
this it is of unusual size in the adult females. In the 
Game breeds pugnacity is developed at a wonderfully 
early age, of which curious proofs could be given ; and 
this character is transmitted to both sexes, so that the 
hens, from their extreme pugnacity, are now generally 
exhibited in separate pens. With the Polish breeds the 
bony protuberance of the skull which supports the crest 
is partially developed J even before the chickens are 
hatched, and the crest itself soon begins to grow, though 
at first feebly ; 31 and in this breed a great bony protu- 
berance and an immense crest characterise the adults of 
both sexes. 
Finally, from what we have now seen of the relation 
which exists in many natural species and domesticated 
races, between the period of the development of their 
characters and the manner of their transmission — for 
example the striking fact of the early growth of the 
horns in the reindeer, in which both sexes have horns, 
in comparison with their much later growth in the 
other species in which the male alone bears horns 
— we may conclude that one cause, though not the sole 
31 For full particulars and references on all these points respecting 
the several breeds of the Fowl, see ‘Variation of Animals and Plants 
under Domestication,’ vol. i. p. 250, 256. In regard to the higher 
animals, the sexual differences which have arisen under domestication 
are described in the same work under the head of each species. 
