SEXUAL SELECTION. 2 71 



of both sexes are characterized by a great bony protuber- 

 ance 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 char- 

 acters 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 effective 

 cause of characters 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 dif- 

 ference 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 forego- 

 ing 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 Avhicli 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 off- 

 spring 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 of love, the cour- 

 age 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 



under Domestication," vol. i, pp. 250, 256. In regard to the higher 

 animals, the sexual differences which liave arisen under domestica- 

 tion are described in the same work under the head of each species. 



