Chap. VIII. Sexual Selection. 22 J 



by secondary sexual characters. Nevertheless, natural selection 

 ■will determine that such characters shall not be acquired by the 

 victorious males, if they would be highly injurious, either by 

 expending too much of their vital powers, or by exposing them 

 to any great danger. The development, however, of certain 

 structures — of the horns, for instance, in certain stags — has been 

 carried to a wonderful extreme ; and in some cases to an extreme 

 which, as far as the general conditions of life are concerned, 

 must be slightly injurious to the male. From this fact we learn 

 that the advantages which favoured males derive from conquer- 

 ing other males in battle or courtship, and thus leaving a 

 numerous progeny, are in the long run greater than those derived 

 from rather more perfect adaptation to their conditions of life. 

 We shall further see, and it could never have been anticipated, 

 that the power to charm the female has sometimes been more 

 important than the power to conquer other males in battle. 



LAWS OF INHERITANCE. 



In order to understand how sexual selection has acted on many 

 animals of many classes, and in the course of ages has produced 

 a conspicuous result, it is necessary to bear in mind the laws of 

 inheritance, as far as they are known. Two distinct elements 

 are included under the term " inheritance " — the transmission, 

 and the development of characters ; but as these generally go 

 together, the distinction is often overlooked. We see this dis- 

 tinction in those characters which are transmitted through 

 the early years of life, but are developed only at maturity 

 or during old age. We see the same distinction more clearly 

 with secondary sexual characters, for these are transmitted 

 through both sexes, though developed in one alone. That they 

 are present in both sexes, is manifest when two species, having 

 strongly-marked sexual characters, are crossed, for each trans- 

 mits the characters proper to its own male and female sex to the 

 hybrid offspring of either sex. The same fact is likewise mani- 

 fest, when characters proper to the male are occasionally deve- 

 loped in the female when she grows old or becomes diseased, 

 as, for instance, when the common hen assumes the flowing tail- 

 feathers, hackles, comb, spurs, voice, and even pugnacity of the 

 cock. Conversely, the same thing is evident, more or less plainly, 

 with castrated mal es. Again, independently of old age or disease, 

 characters are occasionally transferred from the male to the 

 female, as when, in certain breeds of the fowl, spurs regularly 

 appear in the young and healthy females. But in truth they are 

 simply developed in the female ; for in every breed each dekiij 



