20 THE COURTSHIP OF ANIMALS 



and the survival of the race. The former are governed, 

 or determined, by Natural, the latter by Sexual, Selection. 



The sphere of influence of these two factors may be 

 delimited, if we regard natural selection as the factor 

 accountable only for the qualities necessary for the 

 survival of the individual — necessary to ensure success 

 in the struggle for existence. Then it will become 

 apparent that the qualities and attributes necessary to 

 achieve the survival of the race are of a different kind, 

 and these are the factors which are embraced under the 

 term " Sexual Selection." 



It is a mistake to regard animals in relation to the 

 selection theory as if they were so many tailors' " manni- 

 kins." Yet a large number of the critics of the selection 

 theory seem to fall into this error, ignoring all but the 

 most superficial characters. 



The peculiarities of colour, structure and behaviour, that 

 is to say, the characters and qualities which distinguish 

 the individuals of any given race, are due to inherent 

 qualities of the germ-plasm. Each of such qualities, 

 therefore, may be regarded as entities. Selection deter- 

 mines their survival. Intracellular selection is the first 

 sieve through which they have to pass, natural and sexual 

 selection are others, as circumstances may determine. 



As a rule the sex of an individual is attested by more 

 or less conspicuous external features. These are known 

 as the " Secondary Sexual Characters." But no hard-and- 

 fast line can be established for these, at any rate, so far 

 as colour and ornament are concerned, for such, as will 

 become apparent in the course of these pages, tend to 

 appear first in the male, and then, later, to be acquired 

 by the female, until in many cases the two sexes become 

 again indistinguishable. 



