THE GREEK ATTITUDE 



The method or mechanism, by which variations are 

 accomplished, thus requires the inductive method 

 based on observations showing that existing organic 

 forms have a continuous ancestry, gradually changing 

 more and more in form and habits as we extend back- 

 wards our period of time ; the causes of these changes 

 may be either natural or supernatural. But before a 

 theory of evolution as we think of it at the present 

 time, if we eliminate mere guessing, can ever be pro- 

 posed we must have data not only of variations with- 

 in the species but also from species to species and 

 from genus to genus. Thus, a science of evolution re- 

 quires as positive evidence a great store of fossil re- 

 mains of animal and plant life which differ from ex- 

 isting forms. And we must arrange and classify these 

 fossils in a closely related chronological series. The 

 systematic collecting of fossils is then the first necessi- 

 ty; and the second is to develop the science of geology 

 to such a degree of accuracy that we can use the con- 

 clusions of geologists to determine a time record 

 showing when the organism which produced a fossil 

 was living and imbedded in the stratum of rock in 

 which it was found. We then have to rely upon the 

 successive deposition of rock as the clock of the evo- 

 lutionist who must consider the order and thickness 

 of strata as the successive beats of the world-clock. 



We must finally know not only that variation has 

 occurred from generation to generation, but also the 

 causes for variations in past generations and how 



C 73 3 



