446 The American Naturalist. [June, 



The further applications of the principle lead us over into 

 the field of our second question, i. e., phylogeny. 



II. 



Phylogeny : Physical Heredity. — The question of phylogen- 

 etic development considered apart, in so far as may be, from 

 that of heredity, is the question as to what the factors really 

 are which show themselves in evolutionary progress from gen- 

 eration to generation. The most important series of facts re- 

 cently brought to light are those which show what is called 

 " determinate variation " from one generation to another. 

 This has been insisted on by the paleontologists. Of the two 

 current theories of heredity, only one, Neo-Lamarkism — by 

 means of its principle of the inheritance of acquired charac- 

 ters—has been able to account for this fact of determinate 

 phylogenetic change. Weismann admits the inadequacy of 

 the principle of natural selection, as operative on rival organ- 

 isms, to explain variations when they are wanted or, as he 

 puts it, "the right variations in the right place" (Monist, 

 Jan., '96). 



I have argued, however, in detail that the assumption of 

 determinate variations of function in ontogenesis, under the 

 principle of neurogenetic and psychogenetic adaptation, does 

 away with the need of appealing to the Lamarkian factor. 

 In the case i. g., of instincts, " if we do not assume conscious- 

 ness, then natural selection is inadequate ; but if we do assume 

 consciousness, then the inheritance of acquired characters is 

 unnecessary " (ref. 5). 



" The intelligence which is appealed to, to take the place of 

 instinct and to give rise to it, uses just these partial variations 

 which tend in the direction of the instinct ; so the intelligence 

 supplements such partial co-ordinations, makes them func- 

 tional, and so keeps the creature alive. In the phrase of Prof. 



themselves modify the reactions of an organism. . . . The facts show that 

 individual organisms do acquire new adaptations in their lifetime, and that is our 

 first problem. If in solving it we find a principle which may also serve as a prin- 

 ciple of race-development, then we may j 



