378 DARWINISM TO-DAY, 



Let us begin our motto with Ignoramus, but never follow 

 it with Ignoribimus. 



Now if we do not know, but want to know, and are willing 

 to make an attempt toward knowing, where shall our energy 

 Prime needs ^ ex P^ orat i n an ^ discovery be first directed? 5 

 of evolution To what particular points or aspects of the 

 causes-of-evolution problem shall we give our 

 first attention, what fields of study first invade ? What, in a 

 word, is the principal desideratum in present-day investiga- 

 tion of evolution? I should answer, the intensive study of 

 variability. Not alone of the statics of variation but of its 

 dynamics. Indeed, above all its dynamics. The experimental 

 study of the stimuli, external and internal, the influences, 

 extrinsic and intrinsic, which are the factors and causes of 

 variation, this is the great desideratum ; this the crying call 

 to the evolution student. Experiment in variation study 

 includes controlled modification of ontogeny (experimental 

 development) and controlled modification of phylogeny 

 (pedigreed breeding). In the study of variation statics, 

 biometry is the greatest advance in modern methods, and 

 the essential basis of biometric study, namely, quantitative 

 and statistical data, must have its part in the investigation 

 of variation dynamics. But in entering the realm of the 

 causal study of variability, "we must not," as Roux has 

 clearly pointed out, "conceal from ourselves the fact that 

 the causal investigation of organism is one of the most 

 difficult, if not the most difficult, problem which the human 

 intellect has attempted to solve, and that this investigation, 

 like every causal science, can never reach completeness, 

 since every new cause ascertained only gives rise to fresh 

 questions concerning the cause of this cause." 



I believe that the neglect on the part of the selectionists to 

 pay sufficient attention to the origin and causes of the varia- 

 tion which is such an indispensable basis of their theory, has 

 been one of the most obvious reasons for the present strong 



