246 EVOLUTION AND ANIMAL LIFE 



attempt o determine in measurable or quantitative degree just 

 what specific effects each factor produces. Obviously the most 

 reliable way to effect this analysis and this determination of 

 the specific cause and effect relations is to appeal to experi- 

 ment. But biology has always been looked on as, and until 

 recently has actually been, almost wholly a science of observa- 

 tion. It is now becoming, in part at least, a science of experi- 

 ment as chemistry and physics have long been (these are now 

 becoming more and more sciences of calculation, that is, exact 

 sciences like mathematics), and this change and advance for 

 it is truly an advance when a science formerly relying for its 

 facts on observation begins to base its foundations on the 

 results of experiment is due primarily to the modern interest 

 and work in the problem of developmental causes. The search 

 for a rational, causomechanical explanation of the complex 

 and at first sight wholly baffling phenomena of development 

 has been a great stimulus to the bold questioning of many 

 other vital phenomena heretofore looked on as to be explained 

 only by the assumption of a mystic vital force or capacity 

 wholly beyond and foreign to the physicochemical world of 

 matter and force. Mechanism versus vitalism is one of the 

 greatest present-day battles in biology, and nowhere is the 

 struggle keener or are the mechanists more bold in their posi- 

 tion than in the particular field of the processes and factors of 

 development. To the mechanists the play of familiar physico- 

 chemical forces through the complex and unique structure of 

 germ plasm and living tissues has for result all the extraor- 

 dinary outcome of developmental course and outcome; to the 

 vitalists this course and outcome are far too complex and pur- 

 poseful to be explicable without the assumption of an extra- 

 physicochemical force, with a capacity beyond any single or 

 any combination of several physicochemical forces, which 

 they call vitalism. 



There is little need of discussing the great mechanism 

 versus vitalism problem here: it is too difficult a subject, and 

 one as yet too little illuminated by known facts, to introduce 

 into any elementary discussion of evolution matters. But 

 it may not be amiss to call the attention of even the most 

 elementary student of evolution and general bionomics phenom- 

 ena to the obvious fact, that the moment one indulges a 

 penchant for assuming a mystic, extra-physicochemical force 



