Heredity in Protozoa 581 



of structure and action can continue to exist ?* Or to put the 

 question in a way that leads directly toward investigation: What 

 processes lead to the production of lasting combinations, of such 

 complexity of structure and action as are found in organisms ? 



In considering this question, we are struck by the evident fact 

 that certain combinations of the various factors making up the 

 universe are more lasting than others. Two constituents (as gold 

 and oxygen) come in contact; they do not unite, and the combina- 

 tion constituted by their juxtaposition is quickly dissolved by the 

 incidence of other forces. Two other constituents (as iron and 

 oxygen) come into contact; they unite, and the combination result- 

 ing from their juxtaposition is a relatively lasting one. Such 

 varying permanence of different combinations is seen in every 

 field, but it is particularly striking among such complex bodies as 

 go to make up organisms. Here the persistence of certain com- 

 binations and the evanescence of others is commonly spoken of as 

 selection. The combinations which persist are said to be selected. 

 The term is undoubtedly, for certain reasons, an unfortunate one. 



In the study of organisms, as we have seen, one great class of 

 problems lies in the question, How can such complex combinations 

 as organisms be lasting? Now, the study of what combinations 

 are lasting is precisely the study of so-called selection, and so it 

 happens that in the investigation of the processes by which organ- 

 isms have acquired their characteristics, the study of selection 

 necessarily plays a very large part. 



Selection has often been looked at from an extremely narrow 

 loophole, so that only a small part of it has been seen. In a com- 

 mon case, only the fact that certain individual animals are more 

 lasting than others is taken into account; on this selection from 

 among individuals attempts have been made to base an entire 

 theory of organic evolution. It would seem incredible that any- 

 one should suppose the principle of selection to be limited in its 

 operation to this one class of combinations, did not history show 

 that such views have been held. Selection is merely a name for 

 certain aspects of the way the world process takes place. The 



*This formulation of the problem we owe essentially to Jensen ('07), whose valuable paper cannot be 

 too strongly recommended to those who wish to view such problems from a physiological standpoint. 



