THE EVOLUTIONARY CONCEPT 353 



govern inheritance, and which are derived from the events, regularities, 

 and random recombinations of meiosis and fertilization. 



The large shift in emphasis from a study of macroevolution as it has 

 occurred through great extents of time in the past, to the microevolution 

 of today with its preoccupation with strains, races, and subspecies, is 

 not so much a change in subject matter as of attack. Nearly all biologists 

 are agreed that the process is the same and that the forces that are effec- 

 tive in breaking up more or less uniform, continuous populations into 

 segregated, diverging subpopulations are identical with those that over 

 longer extents of time have produced the many major adaptations and 

 differences that distinguish the major groups of organisms. 



