THE MODES OF THE POUR PRINCIPLES. 8 1 



under /, regressive selection, due to the survival of variations pre- 

 viously excluded; and in its indiscriminate aspects under z, indis- 

 criminate elimination. So also election, and isolation, and partition 

 has each its reflexive mode, produced by the action of the members 

 of the species upon each other, and its environal mode, determined 

 by the relations between the environment and the species ; also its 

 regressive aspects, caused by the cessation or reversal of the influence 

 that has been ruling, and its indiscriminate aspects. The letters {j, 

 k, I, z) here used in designating the different forms correspond with 

 those used in the tables given in Chapter VIII. 



4. The Reflexive Mode of Influence. 



The forms of reflexive selection have been more fully worked out 

 than have those of reflexive isolation, or reflexive election, or reflexive 

 partition. Of the forms of reflexive selection, sexual selection is 

 the most familiar; for Darwin discussed its effects on the evolution 

 of the higher animals and especially emphasized its importance in 

 producing the different races of man. It may be found that some 

 of the effects which he attributed to this principle are produced 

 in other ways; but there can be no doubt that in the evolution of 

 mankind it is a factor of the greatest importance. With the advance 

 of civilization the action of natural selection is checked ; but the result 

 is not as disastrous as it otherwise would be but for the increasing 

 stringency of sexual, social, and institutional selection in preventing 

 the marriage of those who are most deficient. Darwin recognized 

 that the forms of sexual selection may not only change without any 

 change in the environment surrounding the species, and without 

 securing any advantage for the species in its relations to the environ- 

 ment, but that it may even establish a standard of selection that is 

 somewhat at variance with the standard maintained by natural selec- 

 tion, and that it may in such cases be the deciding influence, causing the 

 species to lose certain characters which are at the time of the change of 

 some advantage in its relations to the environment. This he thought 

 must have been the case when the ancestors of the human race first lost 

 their covering of hair. (See Descent of Man, Chap. XX.) The em- 

 phasis that Darwin laid on the action of sexual selection in securing 

 the coordination between the sexual instincts of either sex and the 

 instincts and palpable qualities of the other sex has gradually led to 

 the recognition of certain other coordinations between members of 

 the same race, which must be secured by other forms of reflexive selec- 

 tion. These other forms are like sexual selection, in that they are 

 subject to change without change in the environment of the species. 



