THE METHOD OF EVOLUTION FROM THE VIEW- 

 POINT OF A GENETICIST^ 



A. FRANKLIN SHULL 

 University of Michigax 



A SYMPOSIUM upon the method of evolution, participated 

 in by students from widely ditf erent provinces, can hardly 

 be expected to develop harmony of opinion. But to be 

 assigned a place in such a discussion as a representative 

 of one field of endeavor does not imply that the conclusion 

 one reaches will necessarily differ from that of his co- 

 symposiasts; for the question of the method of evolution 

 is a question of fact, and when the fact is discovered, it 

 will be recognized as completely by the paleontologist as 

 by the physiologist. And, in particular, to be assigned 

 the final place in the argument does not mean that the 

 doctrine preached will be, or even is, the last word on the 

 subject. In the present state of knowledge of biology the 

 most that can be ex])ected of an address on this subject is 

 a statcnu'iit of i)riiuM|)l('s which should guide us in a 

 seaicli for tlic facts. I'cyond these principles there are 

 justifiable suspicions, and there may even be militant con- 

 jecture, but little else. 



The first fundamental principle for the guidance of one 

 who would find the method of evolution is a principle 

 common to all sciences which seek to explain the occur- 

 rences of a remote i>ast. Xo a.iicncies may l)e assumed 

 to have oi)eratc(l fifty million years a,i>() of a different 

 order from tiiosc that" op<'ratc to-.lay. If the phenomena 

 of the present affoid a ]»laiisil)lc. or even possible, expla- 

 nation of the past, thei-e must be no appeal to other phe- 

 nomena, tlu' like of which do not now exist. Just as a 

 geologist mentally consti'ucts the rock strata a thousand 



