^JJ6 THE DESCENT OF MAN. 



beetles (Curculioniclae) there is a great difference between 

 the male and the female in the length of the rostrum or 

 snout; * but the meaning of this and of many analogous 

 differences is not at all understood. Differences of structure 

 between the two sexes in relation to different habits of life 

 are generally confined to the lower animals; but with some 

 few birds the beak of the male differs from that of the 

 female. In the Huia of New Zealand the difference is 

 wonderfully great, and we hear from Dr. Buller \ that the 

 male uses his strong beak in chiseling the larvae of insects 

 out of decayed wood, while the female probes the softer 

 parts with her far longer, much curved and pliant beak; 

 and thus they mutually aid each other. In most cases 

 differences of structure between the sexes are more or less 

 directly connected with the propagation of the species; thus 

 a female, which has to nourish a multitude of ova, requires 

 more food than the male, and consequently requires special 

 means for procuring it. A male animal, which lives for a 

 very short time, might lose its organs for procuring food 

 through disuse, without detriment; but he would retain his 

 locomotive organs in a perfect state, so that he might reach 

 the female. The female, on the other hand, might safely 

 lose her organs for flying, swimming, or walking, if she 

 gradually acquired habits which rendered such powers 

 useless. 



We are, however, here concerned only with sexual selec- 

 tion. This depends on the advantage which certain indi- 

 viduals have over others of the same sex and species solely 

 in respect of reproduction. When, as in the cases above 

 mentioned, the two sexes differ in structure in relation to 

 different habits of life, they have no doubt been modified 

 through natural selection, and by inheritance limited to 

 one and the same sex. So again the primary sexual 

 organs, and those for nourishing or protecting the young, 

 come under the same influence; for those individuals which 

 generated or nourished their offspring best, would leave, 

 cceteris paribus, the greatest number to inherit their 

 superiority; while those which generated ornourislied their 

 offspring badly would leave but few to inherit their weaker 

 powers. As the male hae to find the female he requires 



*Kirby and Speuce, "Introduction to Entomology," vol. iii, 1826, 

 p. 309. 



\ " Birds of New Zealand," 1872, p. 66. 



