210 BAiftWmiSM AND HUMAN LIFE 



or scent, but rather the tout-ensemhle of that male 

 who most excites her sexual interest. As Weis- 

 mann says : " Even though we certainly cannot 

 assume that the females exercise a conscious choice 

 of the ' handsomest ' male, and dehberate, Uke 

 judges in a court of justice, over the perfections 

 of their wooers, we have no reason to doubt that 

 distinctive forms (decorative feathers and colours) 

 have a particularly exciting effect upon the female, 

 just as certain odours have among animals of so 

 many different groups, including the butterflies." ' 



Though Darwin sometimes seems to credit the 

 female with no small degree of aesthetic fastidious- 

 ness, he also states that "it is not probable that 

 she consciously dehberates ; but she is most 

 excited or attracted by the most beautiful, or 

 melodious, or gallant males." As Lloyd Morgan 

 says : " The most vigorous, defiant, and mettle- 

 some male is preferred, just because he alone affords 

 a contributory stimulation adequate to evoke the 

 pairing impulse, with its attendant emotional 

 tone." From the human point of view, perhaps 

 the most important point is that, in the course 

 of evolution, sexual behaviour has come to be 

 associated with psychological values which hitch 

 it to the skies. 



Isolation.— Besides selection in its varied forms 

 there is another directive factor in evolution — 

 which Darwin to some extent recognised — and 

 that is Isolation. This term is used to include 

 all the means which restrict the range of inter- 

 crossing within a species : geographical barriers, 

 such as arise when a peninsula becomes an island ; 

 temporal barriers, such as arise when the members 



» " Darwin and Modern Science " (1909), p. 47. 



