WHAT IT IS AND WHAT IT IS NOT. 



55 



It seems to me that the word evolution is now legiti- 

 mately used in four different senses. It is the name of 

 a branch of science; it is a theory of organic existence; 

 it is a method of investigation ; and it is the basis of a 

 system of philosophy. 



As a science, evolution is the study of changing be- 

 ings acted upon by unchanging laws. It is a matter of 

 common observation that organisms 



e science change from day to day, and that day 



of organic j j t j 



evolution "J' ^^^ some alteration in their envi- 



ronment is produced. It is a conclusion 

 from scientific investigation that these changes are 

 greater than they appear. They affect not only the in- 

 dividual animal or plant, but they affect all groups of 

 living things, classes or races or species. No character 

 is permanent, no trait of life without change; and as 

 the living organism and groups of organisms are under- 

 going alteration, so does change take place in the ob- 

 jects of the physical world about them. "Nothing 

 endures," says Huxley, "save the flow of energy and 

 the rational order that pervades it." The structures 

 and objects change their forms and relations, and to 

 forms and relations once abandoned they never return; 

 but the methods of change are, so far as we can see, im- 

 mutable. The laws of life, the laws of death, and the 

 laws of matter never change. If the invisible forces 

 which rule all visible things are themselves subject to 

 modification and evolution we have not detected it. If 

 these vary, their aberrations are so fine as to defy human 

 observation and computation. In the control of the uni- 

 verse we find no trace of " variableness nor shadow of 

 turning." "It is the law of heaven and earth, whose 

 way is solid, substantial, vast, and unchanging." 



But the things we know do not endure. Only the 

 shortness of human life allows us to speak of species or 



