Chap. VIII. Sexual Selection. 239 



io the sexes of the aboriginal parent-species ; yet they acquire 

 their characteristic plumage late in life, for the chickens are 

 distinctly pencilled. With respect to other characters besides 

 colour, in the wild-parent species and in most of the domestic 

 breeds, the males alone possess a well-developed comb ; but in 

 the young of the Spanish fowl it is largely developed at a very 

 early age, and, in accordance with this early development in the 

 male, it is of unusual size in the adult female. In the Game 

 breeds pugnacity is developed at a wonderfully early age, of 

 which curious proofs could be given ; and this character is trans- 

 mitted 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 even before the chickens 

 are hatched, and the crest itself soon begins to grow, though at 

 first feebly; 47 and in this breed the adults of both sexes are 

 characterised by a great bony protuberance and an immense crest. 



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 bear horns, in comparison with their much later growth 

 in the other species in which the male alone bears horns — we 

 may conclude that one, though not the sole cause of characters 

 being exclusively inherited by one sex, is their development at 

 a late age. And secondly, that one, though apparently a less 

 efficient cause of characters being inherited by both sexes, is 

 their development at an early age, whilst the sexes differ 

 but little in constitution. It appears, however, that some 

 difference must exist between the sexes even during a very 

 early embryonic period, for characters developed at this age not 

 rarely become attached to one sex. 



Summary and concluding remarks. — From the foregoing dis- 

 cussion on the various laws of inheritance, we learn that the 

 characters of the parents often, or even generally, tend to become 

 developed in the offspring of the same sex, at the same age, and 

 periodically at the same season of the year, in which they first 



47 For full particulars and re- 250, 256. In regard to the higher 



ferences on all these points respect- animals, the sexual differences which 



ng the several breeds of the Fowl, hare arisen under domestication are 



gee 'Variation of Animals and Plants described in the same work undei 



ander Domestication/ vol, i. pp. the head of each species. 



