LECTURE II. 



EVOLUTION AS A WORKING HYPOTHESIS. 



77. Evolution as a Theory. The theory of the 

 formation of species by divergence and development; 

 in narrower sense, the theory that all forms of life 

 now existing, or that have existed on the earth, 

 have sprung from a few primitive forms, or, more 

 likely, from one. "That whilst this orb has gone 

 circling on in obedience to the fixed law of grav- 

 ity, endless forms most beautiful and most wonder- 

 ful have been or are being evolved." Darwin. 



This theory at first " a working hypothesis." All 

 contrary hypotheses have long since ceased to work. 

 The theory of Evolution as the method of creation of 

 species as well attested as the theory of gravitation. 

 All biological investigation must assume it ; without 

 it most such investigations impossible. Naturalists 

 could no more go back to the old notion of separate 

 creation for each species and its organs, than astron- 

 omers could go back to the pre-scientific notions of 

 guiding angels as agents controlling planetary mo- 

 tions. No naturalist whose studies give him the 

 right to an opinion on the origin of species now holds 

 this view ; no one could hold it and look an animal 

 in the face. 



///. Evolution as a Method of Study. Studying the 

 present in the light of the past. The easy work of 



