

THE FOUR INSEPARABLE FACTORS OF EVOLUTION. 299 



The words influencing and influenced by, which convey the significance at- 

 tached to the interactions of the factors, bring us back to John Stuart Mill's 

 argument that the cause of anything is the total assemblage of the conditions that 

 precede its appearance, but we have no right to give the, name of cause to one of them 

 exclusively of the others: or, more fully, that the cause is the "sum-total of the 

 conditions, positive and negative, taken together, the whole of the contingencies 

 of every description, which being realized, the consequent invariably follows." 



This doctrine formulated by Mill without specific reference to biological 

 phenomena but in relation to physical phenomena in general, nevertheless ex- 

 presses in the clearest possible manner the significance which we here attach to 

 the words inseparable factors. 



Thus excluding the ordinary arithmetical significance of the multiplication 

 sign, we may use it merely as a convenient symbol for the present conception. 



Similarly, the four factors may be symbolized by four capital letters, as 



follows : 



Heredity, h or H 

 Ontogeny, o or O 

 Environment, e or E 

 Selection, s or S. 



A method of representing the factors graphically is to use a light face letter, 

 e. g., h, for the stable and normal condition, and a heavy face letter, e. g. } H, 

 for an abnormal or changed condition. The sequence, or order is indicated 

 by the numerals 1, 2, 3, 4. For example: 



H XO Xt XS = a stable, typical, and normal condition. 



H X x E l X S =a change initiated in environment. 



H X O' X E 1 X ? = a change in environment with a corresponding change in ontogeny. 



H X O 1 X E 1 X S' = a chance of environment 



with 



by ontogenic selection. 



H* X O* X E 1 X S 5 = a change of environment, with 



H'XO'XE X S 



sequent selection, accompanied by 

 heredity. 



l a corresponding change in ontogeny, with con- 

 ied by a favorable "coincident evolution" in 



cells 



(heredity) and expressing itself in ontogeny. 

 H l X O* X E X S 3 = a saltation in heredity, expressed in ontogeny and made permanent by selection. 



H'XO' XE'XS'=a saltation in heredity, expressed in ontogeny, made permanent by selection, 



leading an organism into a new environment. 



The above formulae are convenient because they clearly express our ideas or 

 the results of experiment as to the initial and consequent primary and secondary 

 relations of the four factors. 



Through the Law of the Inseparable Factors we are prepared to enter upon 

 any form of experimental work or any line of exact observation or statistical 

 inquiry with a perfectly clear understanding of how our facts should be collected 

 and under what group or groups of factors they should be placed. (See Appendix, 

 p. 307.) 



Changes either in the form or in the origin of new characters are not simul- 

 taneously initiated by the four factors; on the contrary, we are prepared to 

 answer the following inquiries : 



