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’ “mannikins.” 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 determines 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. CHAPTER II “MANKIND IN THE MAKING” The use of the term “Courtship”—Primitive Man and the Foundations of Society—“Amorousness” as a motive force—Polygamy—Our half human ancestors—Standards of Beauty—Disquieting signs. Our ideas on the subject of the “Courtship” of animals are of necessity largely framed on what has been observed by each of us in regard to our own race; and without any very careful analysis of motives, or thought of what lies behind. But no real insight into this most tremendous subject can be gained which does not strive to penetrate beyond what is actually seen; which does not endeavour to get at the source of conduct in this regard.