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SCIENCE. 



[N. S. Vol. VII. No. 178. 



i. e., the parent organism must be more de- 

 veloped than the germ cell it propagates. 

 Inheritance is the completing of the devel- 

 opment of the germ as a separate body after 

 generation in the likeness of the parent 

 from which it was separated. 



The fourth factor, variability, is the 

 primary genetic phenomenon of all organ- 

 isms which, in a particular case, rela:tively 

 or entirely ceases with the acquirement of 

 inheritance in the course of development, 

 or with the acquirement of fixation and 

 permanence of specific form in evolution. 

 It may be regarded as the most direct and 

 characteristic expression of genetic energy. 



The next three factors, ratio of increase, 

 struggle for life and natural selection, are, 

 as vital phenomena, of a purely secondary 

 nature. Each of them implies the previous 

 operation in the same organism of develop- 

 ment, variation and the acquired phenom- 

 enon of generation. The discussion of these 

 factors, though of extreme interest for 

 other purposes, and by many considered to 

 be the chief causes of evolution, do not ap- 

 pear as true determining causes of modifi- 

 cation, but causes rather of removal from 

 the field of such organisms as cease to con- 

 tinue in the race. This point was granted 

 by Darwin, as Cope reminded his readers 

 in ' Primary Factors of Evolution.' He 

 held that natural selection does not induce 

 variability; 'it implies only the preserva- 

 tion of such variations as arise and are 

 beneficial.' 



In making this statement it is important 

 to note the distinction between variability 

 and variation. A variation which is trans- 

 mitted or preserved by natural selection 

 loses its variability exactly to the extent 

 of its preservation ; therefore, natural selec- 

 tion checks variability. 



The factors of indirect and direct action 

 of the external conditions of life, and 

 use and disuse," which in the Darwin- 

 ian and Lamarckian theories of evolu- 



tion play so important a part as causes 

 of variation, cannot hold their place of 

 supreme importance if, as is here main- 

 tained, variation be the fundamental factor 

 in genetic problems. From this latter 

 point of view the organism is conceived of, 

 not as passively shaped by the conditions of 

 environment, but as finding its fundamental 

 function in actively occupying environ- 

 ment ; and adjustment is a positive active 

 process involving constant modification. 

 Adjustment is, thus, a result of successful 

 varying, rather than varying a result of 

 maladjustment. Prom this point of view 

 the factors, external conditions of life, use 

 and disuse, struggle for life, and natural se- 

 lection, though operative in determining the 

 course of developmental construction of the 

 -organism, are effective in the way of limit- 

 ing, restricting, giving permanence to and 

 making hereditary tlie characters which 

 arise by the direct activity of genetic energy. 



The tenth factor, divergence of charac- 

 ters, which by Darwin was conceived 

 of as the direct result of the action of the 

 above factors, is, according to this view, a 

 characteristic genetic phenomenon, taking 

 place with greater or less rate of progress 

 in every organic series. It is organic 

 evolution, proper, and consists in the ac- 

 quirement, by a particular living organism, 

 in the course of its individual development, 

 of characters not possessed by its ances- 

 tors. The first step in such evolution is 

 necessarily variation. 



This analysis of the Darwinian factors of 

 evolution presents us with two classes of 

 phenomena, viz.: 



I. Three of them are fundamental phe- 

 nomena exhibited by every living organic 

 body, and it would appear (although not 

 always visibly, still theoretically) continu- 

 ously during active existence of the organ- 

 ism. These have been called genetic phe- 

 nomena, because they are constantly result- 

 ing in genesis of changed state, condition or 



