CONTENTS OUTLINE. ix 



LAWS OF HEREDITY 79 



Uninterrupted or continuous transmission, 79; interrupted or 

 latent transmission, 79; sexual transmission, 79; mixed or mutual 

 transmission, 79; abridged or simplified transmission, 80. 



SEXUAL SELECTION 80 



Law of battle, 81; preferential mating, 81; Darwin's and Wallace's 

 views compared, 82; relation of color of male to vitality and vigor, 

 82; color as related to integumentary expanse and complexity, 83. 



EVIDENCE or SELECTION BY THE FEMALE 84 



Peckham on sexual selection among spiders, 84; Wallace's ex- 

 planation of sexual display by male birds, 85; the house-finch 

 as an illustration of selection, 86; objection that each bird finds 

 a mate, 87. 



DIFFICULTIES IN THE THEORY OF SEXUAL SELECTION AND ALTERNATIVE 



HYPOTHESES 88 



Beddard on sexual dichromatism without selection, 89; difficulty 

 of believing in a highly developed aesthetic sense in birds, 90; 

 Stolzman's view of bright colors and appendages of male birds, 

 91; Eomanes' reply to Wallace's objections, 92; Wallace on the 

 aesthetic sense in relation to sexual selection, 93; Poulton on the 

 same, 94; Morgan on the aesthetic taste of birds, 95; the beautiful 

 in inorganic nature contrasted with the beauty of birds and in- 

 sects, 96; Weismann on novelty as the cause of sexual selection, 

 97; Romanes on the beautiful among the lower forms of life, 97; 

 coloration viewed from a general standpoint, 98; colors which 

 have been evolved with reference to some percipient being, 99; 

 implications of the theory of sexual selection, 100; Grant Allen 

 on the mechanical explanation of the pleasure derived from color 

 combinations, 100; the pleasure given to birds by color combina- 

 tions is of this lower order, 101; synthesis of factors involved in 

 the production of the sexual character of birds, 102. 



THE NATURE OF SPECIES 103 



ON THE MEANING AND LIMITATIONS OF THE TERM '..... 103 



Natural and artificial modes of classification, 103; the basis of a 

 natural system, 103; relativity of the term species, 104; definition 

 of species as used in science, 105. 



ON THE RELATION OF EVOLUTION TO SPECIES 106 



Species necessary for rationality in evolutionary progression, 106; 

 Romanes on the preservation of the species by natural selection, 

 106; objections to Romanes' view, 107; reproduction as growth 

 beyond the individual as an explanation of the origination of 

 altruistic characters and traits, 108; necessity for natural selection 

 to preserve family, and in some instances the tribe, but not the 

 species, 109. 



