SUMMARY 83 



Sexual selection : 



The exercise of choice in mating, observed among spiders, 

 insects, and vertebrates. It results in the developing of 

 courting habits, of conspicuous colors, ornamental append- 

 ages, beauty (?) of voice, etc., which tend to make the 

 individuals of one sex (usually the males) attractive to those 

 of the other sex. 

 Segregation : 



By which the individuals of a species are divided into different 

 groups which do not freely interbreed. The causes of seg- 

 regation are various : geographical, climatic, physiological, 

 aesthetic, etc. 

 Inheritance of parental modifications : 



This is probably an efficient cause of evolution among unicellu- 

 lar organisms, but apparently is not effective among higher 

 animals and plants. 



And we have seen that all of the processes of evolution necessarily centre 

 in reproduction. 



