The Choice and Fixation of Variations 37 



swers some purpose in use or trade, and it is not a variety 

 when it is so much like some other variety that it has no 

 merit that the other does not possess. 



As soon as a plant appears with some features which 

 are more desirable than anything that has preceded it, 

 therefore, it may be the beginning of a new variety. Man 

 chooses it, and then propagates it. This is human selec- 

 tion. If nature did the same thing, it would be natural 

 selection. 



It must not be understood that there are no definite 

 species hi nature. Some plants are so distinct, and so 

 constant in their characters, as to leave no doubt. But 

 wide variability is very common, and it may obscure the 

 relationship. 



Adaptation in nature. Now, how does nature preserve 

 or fix this type ? She does not preserve it. She simply 

 chooses it as a beginning and gradually modifies it and 

 shapes it into the form which she needs. She has no 

 permanent forms. There is a general onward progression 

 of one type either towards other types or towards ex- 

 tinction. We have seen that nature is constantly choosing 

 and selecting. If she selects an individual for the be- 

 ginning of a race, then she selects just as keenly from every 

 offspring of that individual, and so on to the end of time. 

 The process never stops. So nature fixes her forms by 

 keeping them moving, growing, constantly developing 

 farther away from their beginnings. 



The vexed question as to whether there is an accumula- 

 tive effect in variation, need not be considered here, as it 

 is foreign to the particular point of view at this place. 



Artificial selection. Now, man does the same thing. 



