632 Causes and Course of Organic Evolution 



exaggerated outcome of proenvironal planning, the complex 

 though compact knife has been evolved that carries from 10-30 

 separate implements, such as knife-blades, file, corkscrew, 

 chisel, and many other parts. Such an instrument also is a 

 striking illustration of a compounded resultant, built up by 

 uniting the resultants of various distinct stimuli into one cor- 

 related whole. 



The writer has lived through the period during which the 

 proenvironal evolution of two instruments of marvelous per- 

 fection has been going on, viz., the bicycle and the automobile. 

 As a small boy he had the tradition of an uncle who planned 

 and put into practice a small carriage that was difficultly 

 propelled on four wheels by foot treadles inside. But as a 

 young schoolboy he saw this further perfected into the heavy 

 cumbrous tricycle of forty to forty-five years ago. Each 

 inventor-proenvironer — as we might well say — who turned 

 his thoughts to it, took all the best points of previous con- 

 structions, as definite stimuli toward better results. These 

 he united into a new resultant stimulus in the ganglionic cells 

 of the cerebrum, and evolved therefrom a plan that was an 

 advance in the bearings, the couplings, the wheels, the seat, 

 and so on, till the popular tricycle of 30 years ago resulted. 

 In some points the improvements represented advancing vari- 

 ations of a very gradual kind, in others they constituted dis- 

 tinct breaks or mutational changes. 



But even then a daring proenvironer had thought out and 

 realized the high bicycle with large and small wheels, that 

 for younger spirits soon put the tricycle in the shade. And 

 this truly represented a mutational evolution. Such how- 

 ever was chased out in turn by the low-set, high-speed geared 

 bicycle of the past decade, that is now being superseded in 

 part by the autocycle. To those constructors and enthu- 

 siasts who followed closely all of the changes introduced, these 

 were almost as gradual and imperceptible — because of their 

 satisfying approi)riateness — as have been the changes under- 

 gone by some cultivated plants and domesticated animals 

 during the past century or millennium. 



