Nature of Evolutionary Progress 49 



laws of action shall be exemplified at any particular 

 moment. When new conditions arise, new laws of ac- 

 tion are exemplified ; but they are to be formulated in 

 terms of the conditions just as were the old laws. And 

 all the old laws remain in effect so far as the condi- 

 tions they specify continue to prevail; the new laws 

 are merely added to them as they are discovered. 



Biological science lends no support to the doctrines 

 of indeterminism that have become rife in certain 

 branches of physical science. The organization of 

 science is made possible by the prevalence of experi- 

 mental determinism. Experimental determinism con- 

 sists in the observed fact that later perceptual diver- 

 sities between two sets of phenomena are preceded by 

 earlier perceptual diversities, so that if the earlier 

 diversities are removed by experiment the later ones 

 likewise disappear. The farther investigation is 

 pushed in things biological, the more complete be- 

 comes the prevalence of such determinism. The his- 

 tory of biological science is one of steady progress in 

 the discovery of experimental determiners for bio- 

 logical happenings. It leads by induction to the con- 

 clusion that there is no bar to the extension of this 

 kind of knowledge to any case whatever; in other 

 words, to the conclusion that experimental deter- 

 minism holds throughout all things, and that any 

 diversity of results is preceded by a diversity of con- 

 ditions. But this does not mean that all action is 

 stereotyped and predictable. It does not imply that 

 a given individual's actions are predestined, fixed 

 by conditions that existed before he came into being ; 



