SEXUAL SELECTION 315 



whicli exists in many natural species and domesticated 

 races, between the period of tlie development of their char- 

 acters and the manner of their transmission — for example, 

 the striking fact of the early growth of the horns in the rein- 

 deer, 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, caiise 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 charac- 

 ters being inherited by both sexes is their development at 

 an early age, while the sexes differ but little in constitution. 

 It appears, however, that some difference must exist be- 

 tween 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 

 discussion 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 appeared in the parents. But these 

 rules, owing to unknown causes, _ are far from being fixed. 

 Hence, during the modification of a species, the successive 

 changes may readily be transmitted in different ways; some 

 to one sex, and some to both; some to the offspring at one 

 age, and some to the offspring at all ages. Not only are the 

 laws of inheritance extremely complex, but so are the causes 

 which induce and govern variability. The variations thus 

 induced are preserved and accumulated by sexual selection, 

 which is in itself an extremely complex affair, depending, 

 as it does, on the ardor in love, the courage, and the rivalry 

 of the males, as well as on the powers of perception, the 

 taste, and will of the female. Sexual selection will also be 

 largely dominated by natural selection tending toward the 

 general welfare of the species. Hence the manner in which 



