30 Comparative Conceptions 



I think, to the neglect of the recognition of it in seeking 

 genetic explanations. For example, sexual selection re- 

 quires correlation between the organic characters of col- 

 oration, etc., in the male, and the mental apprehension and 

 the sexual impulse of the female. So the evolution of 

 infancy requires correlation between the physical helpless- 

 ness of the young, and the maternal instinct and affection 

 of the mother. In the evolution of gregarious life we find 

 a vast system of correlations of physical characters, 

 expressions, attitudes, behaviour in general which are 

 interpreted and responded to psychologically by other 

 members of the group ; these physical and psychological 

 characters together make up the psychophysical equip- 

 ment of the individuals for their common life. In a later 

 place (Appendix C) the possibility of correlation between 

 mental characters and sexual variations is pointed out in 

 connection with Pearson's theory of ' reproductive selec- 

 tion.' It is remarked also in the same place, that one great 

 form of isolation, that due to social barriers which create 

 segregation and preferential mating, and so effect physical 

 evolution, is not noticed by Romanes in his description of 

 the different forms of isolation ; here there is involved a 

 correlation between the mental functions embodied in per- 

 sonal choice, social convention, law, etc., and colour of skin 

 or other physical characters which either attract or repel. 

 The theory of 'secondary sexual characters' in man and 

 woman extends to mental traits, and points out correlations 

 not only between many characters in the same individual, 

 but also between these of individuals of the opposite sex. 

 The theoretical importance of this sort of correlation 

 appears more fully when we look closely at what it involves. 

 In the first place, negatively : if it be true that the unit of 



