May 27, 1898.] 



SCIENCE, 



727 



must be predicated for the purely genetic 

 phenomena of organisms, to account, that 

 is, for the particular course of development 

 followed by each species, and the particular 

 course of divergence seen in each line of 

 evolution. These conclusions seem to rest 

 on as valid a foundation as that the visible 

 colors of bodies are determined by light 

 energy, or that the temperature phenomnena 

 of physical bodies are determined by heat 

 energy. 



APPLICATION OF THE THEORY OF GENETIC 

 ENERGY. 



The application of this theorij of genetic 

 energy will become evident by attempting 

 to distribute, in accordauce with it, such a 

 set of vital phenomena as are grouped to- 

 gether ia Darwin's list of factors of evolu- 

 tion, la the ' Origin of Species ' Darwin 

 gave the following brief summary of the 

 factors entering into the origin of species : 



" These laws, taken in the largest sense, 

 being growth, with reproduction ; inherit- 

 ance, which is almost implied by reproduc- 

 tion ; variability, from the indirect and di- 

 rect action of the external conditions of life, 

 and from use and disuse ; a ratio of increase 

 so high as to lead to a struggle for life, and 

 as a consequence natural selection, entail- 

 ing divergence of characters and the extinc- 

 tion of less improved forms." 



In this list eleven distinct factors are 

 named. The question arises : What is the 

 place of each in a system of vital phenom- 

 ena in which variability is assumed to be 

 the most fundamental of all ? 



The first factor, growth, in so far as it in- 

 cludes the material increase of the living 

 body by the acquirement of matter from 

 outside, and the reduction of it to a living 

 state in metabolism, is one of the three 

 forms of the fundamental genetic phenom- 

 ena of variability. 



The second factor, reproduction, is made 

 up of two distinct phenomena : (a) the act 



of separating a living body into two or more 

 distinct units, precisely called generation ; 

 and (h) the process by which the individual 

 body is constructed after the fashion of its 

 immediate ancestors, precisely called de- 

 velopment, (a) The first, generation, is a 

 mechanical phenomenon, not necessary or 

 fundamental to all living ; for it is not con- 

 tinually occurring, nor is it possible to occur 

 till after some degree of development is 

 accomplished. Hence, we may assume that 

 it is an acquired phenomenon, i. e., an ex- 

 pression of interaction between the genetic 

 energy of the organism and the energies of 

 the materials of construction and the en- 

 vironment. (6) The second, development, is 

 the second form of the fundamental process 

 above described, and is a necessary and 

 univei'sal characteristic of all living bodies. 

 In Darwin's list the phenomena of develop- 

 ment are partly included under the term 

 growth, but material increase is not neces- 

 sarily development. Metabolism is the 

 acquirement and vivifying of inert matter 

 by and into an individual organism ; de- 

 velopment is the differentiation of this mass 

 into increased complexity of organization 

 and function. 



The third factor, inheritance, is the name 

 for the law observed in the course of devel- 

 opment by which the living body success- 

 ively assumes the characters of the other 

 body from which it was separated in gener- 

 ation. This law of repetition of the char- 

 ters of ancestors cannot be a fundamental 

 phenomena, because if it were strictly car- 

 ried out no development would take place, 

 and evolution results only by ignoring or 

 transgressing the law of inheritance. We 

 must assume, therefore, that inheritance is 

 acquired, and in any series of organisms 

 the law of inheritance became operative 

 only after generation had arisen, and after 

 the attainment of some degree of inequality 

 had been reached between parent and off- 

 spring at the point of the act of genei-ation, 



