INTRODUCTORY 3 



4. Fourth, progressiveness is a salient feature of evolution. 

 Organisms were at first simple; in later ages some of these 

 have transformed into complex highly differentiated animals 

 and plants. From blobs of jelly-like material, responding 

 inadequately to a few of the forces of nature, have developed 

 organisms with elaborate sense organs and organs of 

 response; creatures whose behavior is minutely and ade- 

 quately correlated with processes in the surrounding world. 



But progressiveness, like adaptation, is not a universal 

 feature of evolution. Highly developed organisms may de- 

 generate into parasites, and many organisms still exist that 

 have not developed beyond the lower grades of the organic 

 scale. Whatever brings about evolution must be able to pro- 

 duce progress; but it may produce also its opposite. 



5. Fifth and finally, as to the method of progress when prog- 

 ress occurs, we must accept as a fact I believe the reports of 

 students of progressive evolutionary series among fossil organ- 

 isms such as are known in the development of the horse or 

 the elephants. They report that progress in such series is 

 continuous, gradual, by slight changes, not by sudden leaps. 

 Continuity, not discontinuity, is the characteristic of such 

 progressive series.^ 



Genetic variations, to be adequate to the production of 

 evolution, must then be of a sort to produce these five salient 

 features: transformism, diversification, adaptation, progres- 

 siveness and continuity. 



And now, certain points as to the nature of genetic varia- 

 tions. In order that variations shall play a part in evolution, 

 they must be inherited ; they must affect, not single individ- 

 uals only but their descendants, becoming thus characteristics 

 of a race or species. Only such can be called genetic variations. 



1 See the notes at the end of each chapter. 



