2 GENETIC VARIATIONS 



now see evolution occurring, as it sees inheritance occurring ? 

 Are the known types of genetic variation adequate to bring 

 about the salient features of organic evolution ? These are the 

 questions with which we wish to deal. 



What are the salient features of organic evolution ? If we 

 could watch the procession of living things from the begin- 

 ning of life on the earth, what kinds of changes would we 

 see? We can I believe list the main types of change under 

 five heads: 



1. First, evolution is transformism. Organisms do not re- 

 main constant, but slowly change with the passage of time, as 

 a developing child changes with the passage of time. 



2. Second, evolution is diversification. Organisms trans- 

 form, not in one direction only, but in many directions. From 

 an early simple situation is produced that which we now see 

 about us: great numbers of animals and plants that are di- 

 verse in many ways. 



3. Third, evolution brings about adaptation. Organisms 

 develop structures and functions that tend to keep them in 

 existence; to ward off dangers in a varied and changing 

 world, and to obtain conditions favorable for their internal 

 processes. Different organisms become adapted to different 

 conditions. Otherwise expressed, evolution produces struc- 

 tures and functions that bring about ends, of the sort that in 

 human beings become the object of conscious purpose. And 

 evolution produces, in man at least, some organisms whose 

 behavior is consciously purposive. 



But, what is also important, there are produced, too, organ- 

 isms that are not adaptive; organisms that fail to develop or to 

 survive under the conditions of existence; a fact to which we 

 shall have to recur. Adaptation is produced in evolution, but 

 is not universal in the products of evolution. 



