82 ORGANIC EVOLUTION 



phenomena of cell structure and physiology, which it is not 

 appropriate to describe here. 



In closing this exposition of the theory of organic evolu- 

 tion it is well to call attention to one important point. The 

 whole process of evolution centres in the processes of repro- 

 duction. Natural selection is the selection of the individuals 

 who are to perpetuate the species, and not merely of the indi- 

 viduals who are to live out their own lives. Sexual selection is 

 the selection of mates in breeding. Segregation is the preven- 

 tion of free intercrossing in the breeding processes. Parental 

 modifications can produce an effect upon the evolution of the 

 species only when they are handed down by reproduction to 

 the following generations. The offspring of the next gen- 

 eration, and not the adults of the present generation, are 

 the goal in all the processes of evolution. Much inaccu- 

 rate thinking has been due to the failure to clearly grasp 

 this fundamental conception. Lloyd Morgan sums the 

 matter up in the phrase, " To breed or not to breed. 

 That's the question." 



SUMMARY 



In the foregoing rapid review we have noted the manner of operation 

 of these 



Factors of evolution : 

 Natural selection : 



Heredity (Offspring tend to resemble their parents) : 

 Variation (This resemblance is far from exact) : 

 The destruction, in the struggle for existence, of the individuals 

 which are not adapted to their environment, resulting in a 

 more and more perfect adjustment of organisms to the con- 

 ditions in the midst of which they have to live. 



