INTRODUCTION 13 



of sexual selection. He was influenced in the train of 

 thought which he followed up with such brilliant success 

 by what he had observed in the behaviour of highly- 

 ornamented species, such as the Peacock and the Birds 

 of Paradise. The strange antics of these birds when under 

 the influence of sexual excitement persuaded him that 

 they were at least dimly conscious of their splendour, and 

 of its power to fascinate. The female, on the other hand, 

 was supposed to be coy, and to bestow her person on the 

 finest performer. In this way the dullest birds and the 

 poorest performers were gradually eliminated. Here, 

 indeed, was sexual selection. The frills thus begotten he 

 called " Secondary Sexual Characters," a term which is 

 also used, and was used, by him, to include any feature 

 whereby the sexes can be distinguished apart from the 

 character of the genital organs. 



•^ Horns, tusks, and spurs are other forms of secondary 

 sexual characters. And these stand for another form oJ 

 sexual selection — that of selection by battle. Herein 

 victory falls to the strongest and most pugnacious male 

 who, as the spoils of victory, annexes the females which 

 formed the subject of the duel. This theory, which must 

 be discussed at greater length in the course of these pages, 

 has had many critics, and among them men of mark. But 

 whatever modifications may be deemed necessary, they 

 will be such as are demanded by the results of later dis- 

 coveries rather than to the force and subtlety of the 

 arguments of his opponents. 



One of the most formidable of the opponents of the 

 Sex lal Selection theory was Wallace. But his arguments 

 were far from convincing, and often inconsistent. He 

 attributed the more frequent occurrence in male animals 

 of brilliant coloration and exaggerations of growth such 



