284 THE FOUR INSEPARABLE FACTORS OF EVOLUTION. 



First : what appears in individuals, varieties, and species, as observed by the 

 describer or systematist. 



Second: the unseen forces of heredity which underlie these appearances. 



This profound distinction between the "character" as it appears to us as the 

 soma and the " character" as it exists in the blastos is one which we owe to the 

 studies in heredity of Galton, Weismann, Mendel, and Johannsen. It is 

 pressed as follows : 



ex- 



Sum of characters of the soma = Heredity, Ontogeny, Environment. 

 Sum of characters of the blastos = Heredity. 



The sum of "characters" in the soma has been aptly termed by Johannsen 

 the phenotype , the sum of "characters," or "genes," in the blastos the genotype. 



Into every organism we examine enter the three factors heredity, ontogeny, 

 environment. It is easy to understand why the soma is more readily disturbed 

 than the blastos, because every soma is the resultant of three factors, while 

 the blastos is relatively undisturbed. 



I. SPECIAL ACTION OF EACH OF THE FACTORS. 



Biologists are in a general way familiar with what is comprised in each of the 

 four factors under consideration, but the literature at least is so full of apparent 

 misunderstanding that the author may be pardoned for elaborating somewhat 

 his own interpretation of the precise biological or evolutional significance of 

 each of these factors. 



1. Environment. 



i 



Under environment we should consider the sum total of purely inorganic and 

 organic external conditions, with the exception of selection which forms a com- 

 plex of its own; that is, conditions which are neither germinal nor somatic, which, 

 however, as "conditions of life" affect the heredity, the ontogeny, and the 

 selection or elimination of the individual. The older conceptions of the con- 

 ditions of life, Le milieu, La monde ambiente, should be taken into consideration 

 together with the "continuity of environment," that is, the continuation of 

 inheritance of similar environment from generation to generation ; in other words, 

 with ancestral environment as contrasted with discontinuity of environment or 

 the introduction of new or changed conditions. 



It is impossible to make a complete classification of environment, but the 

 following scheme, partially suggested by that of Max Verworn, is suggestive of 

 the multiplicity of conditions. 



It will be observed that organic environment brings us into close touch witn 

 the phenomena of competition and selection. 



1 Osborn, H. F., Environment in its Influence upon the Successive Stages of Development and 

 as a Cause of Variation. Opening discussion before the American Society of Naturalists, Baltimore, 

 Dec. 27, 1894. Science, N. S., vol. I, No. 2. Jan. 11. 1895. dd. 35-36. 



