1909.] CONKLIN— THE WORLD'S DEBT TO DARWIN. liii 



in the living world, but not the original properties of life. It under- 

 takes to explain the various forms of adaptations found in the living 

 world, but not protoplasmic adaptability. If life is "continuous 

 adjustment of internal relations to external relations," as Herbert 

 Spencer held, then life is adaptability, and it would be unreasonable 

 to demand that any theory of organic evolution should explain the 

 origin of this. 



It may be that regulation or regeneration is one of the funda- 

 mental physiological properties of living things and that it belongs 

 in the same category with assimilation, growth, metabolism, repro- 

 duction and irritability, properties which are found in the lowest 

 organisms as well as the highest, and which can therefore be left 

 out of the list of those things which evolution may reasonably be 

 expected to explain. 



On the other hand it seems possible that many contingent, indi- 

 vidual adaptations may find a natural explanation in the further 

 extension of the selection principle to the physiological responses 

 of organisms and to the more elementary parts of which their bodies 

 are composed. If to the natural selection of Darwin ("personal 

 selection ") there be added some such principles as the struggle of 

 the parts (" histonal selection") of Roux, the "germinal selection" 

 of Weismann and the method of "trial and error" of Jennings, 

 many adaptations, otherwise inexplicable may find a natural expla- 

 nation. Weismann's views have been frequently condemned because 

 of their highly speculative character, but it cannot be denied that he 

 has shown profound insight into the most fundamental problems of 

 biology, and in many instances he has seen his speculations verified 

 by subsequent research. In a masterly series of works Jennings has 

 proved that the adaptations shown in the behavior of many lower 

 organisms may be reduced to the simple principle of " trial and 

 error," or the rejection of unfavorable motor responses; in this way 

 aparently purposive behavior, which Binnet supposed to be due to 

 .the relatively complex "psychic life of microorganisms" has been 

 shown to be due to a few simple motor reflexes, which are repeated 

 indefinitely until they bring the organism into a favorable environ- 

 ment. Darwin himself suggested this explanation of the appar- 

 ently intelligent behavior of the earthworm, and Jennings has shown 



