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SCIENCE 



[N. S. Vol. XLI. No. 1044 



tical use in our investigations on living 

 things, or find their justification on larger 

 grounds of scientific expediency. How- 

 ever philosophy may answer, science can 

 find but one reply. The scientific method 

 is the mechanistic method. The moment 

 we swerve from it by a single step we set 

 foot in a foreign land where a different 

 idiom from ours is spoken. We have, it is 

 true, no proof whatever of its final validity. 

 We do not adopt the mechanistic view of 

 organic nature as a dogma but only as a 

 practical program of work, neither more 

 nor less. We know full well that our pres- 

 ent mechanistic conceptions of animals and 

 plants have not yet made any approach to 

 a complete solution of the problems of life, 

 whether past or present. This should en- 

 courage us to fresh efforts, for just in the 

 present inadequacy of these conceptions lies 

 the assurance of our future progress. But 

 the way of unverifiable (and irrefutable) 

 imaginative constructions is not our way. 

 We must hold fast to the method by which 

 all the great advances in our knowledge of 

 nature have been achieved. We shall make 

 lasting progress only by plodding along 

 the old, hard beaten trail blazed by our 

 scientific fathers — the way of observation, 

 comparison, experiment, analysis, syn- 

 thesis, prediction, verification. If this 

 seems a prosaic program we may learn 

 otherwise from great discoverers in every 

 field of science who have demonstrated how 

 free is the play that it gives to the con- 

 structive imagination and even to the fac- 

 ulty of artistic creation. 



Thus far I have desired to emphasize 

 especially the reawakening of our interest 

 in problems of the present, and the grow- 

 ing importance of experimental methods in 

 our science. It is interesting to observe 

 how these changes have affected our atti- 



tude towards the historical problem as dis- 

 played in the modern study of genetics. 

 Even here we are struck by the same shift- 

 ing of the center of gravity that has been 

 remarked in other fields of inquiry. In 

 the Darwinian era studies on variation and 

 heredity seemed significant mainly as a 

 means of approach to the problems of evo- 

 lution. The post-Darwinians awoke once 

 more to the profound interest that lies in 

 the genetic composition and capacities of 

 living things as they now are. They 

 turned aside from general theories of evo- 

 lution and their deductive application to 

 special problems of descent in order to take 

 up objective experiments on variation and 

 heredity for their own sake. This was not 

 due to any doubts concerning the reality of 

 evolution or to any lack of interest in its 

 problems. It was a policy of masterly in- 

 activity deliberately adopted; for further 

 discussion concerning the causes of evolu- 

 tion had clearly become futile until a more 

 adequate and critical view of existing ge- 

 netic phenomena had been gained. Investi- 

 gators in genetics here followed precisely 

 the same impulse that had actuated the em- 

 bryologists ; and they, too, reaped a rich 

 harvest of new discoveries. Foremost 

 among them stands the re-discovery of 

 Mendel's long- forgotten law of heredity — 

 a biological achievement of the first rank 

 which in the year 1900 suddenly illumi- 

 nated the obscurity in which students of 

 heredity had been groping. Another tow- 

 ering landmark of progress is De Vries's 

 great work on the mutation theory, pub- 

 lished a year later, which marked almost 

 as great a transformation in our views of 

 variation and displayed the whole evolu- 

 tion problem in a new light. In the era 

 that followed, the study of heredity quickly 

 became not only an experimental but al- 

 most an exact science, fairly comparable 

 to chemistry in its systematic employment 



