96 A Factor in Evolutioii 



tions in each generation's development} in which the con- 

 genital afid the acqitired unite to produce a definite or 

 determinate direction of change. Those individuals in 

 which this union of the two factors does not occur 

 are — apart from other possible reasons for survival — 

 incapable of maintaining the struggle for existence, and 

 are eliminated. 



The further applications of the principle lead us over 

 into the field of our second question, that of phylogeny or 

 evolution. 



§ 3. Effects of Individual Accommodation on Evolution 



Phylogeny: A. Physical Heredity. — The question of 

 phylogenetic descent considered apart, in so far as may 

 be, from that of heredity, is the question as to v^rhat the 

 factors really are which show themselves in evolutionary 

 progress from generation to generation. The most impor- 



i"It is necessary to consider further how certain reactions of one single 

 organism can be selected so as to adapt the organism better and give it a Ufe 

 history. Let us at the outset call this process ' Organic Selection ' in con- 

 trast with the Natural Selection of whole organisms. ... If this (natural 

 selection) worked alone, every change in the environment would weed out all 

 life except those organisms which by accidental variation reacted already in 

 the way demanded by the changed conditions — in every case new organisms 

 showing variations, not, in any case, new elements of life history in the old 

 organisms. In order to the latter we should have to conceive . . . some 

 modification of the old reactions in an organism through the influence of 

 new conditions. . . . We are, accordingly, left to the view that the new 

 stimulations brought by changes in the environment 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 principle of race- 

 development (evolution), then we may possibly use it against the * all- 

 sufficiency of natural selection' or in its support" {Mental Development^ 

 1st ed., pp. 175-176) — quoted as an early statement (1895) ®^ ^^^ essential 

 idea involved in this chapter. Cf. also p. 158, below. 



