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THE FOUR INSEPARABLE FACTORS OF EVOLUTION. 279 



result." Thus, for example, it is claimed that "light is the most powerful 

 factor amongst all the agents which influence life upon the earth." Thus 

 Wallace in 1 889 wrote : ' ' The importance of natural selection as the one invariable 

 and ever-present factor [italics our own] in all organic change and that which 

 alone has produced the temporary fixity combined with a secular modification of 



species. ' ' 



There is a perpetual balance between these four factors or complexes of con- 

 ditions, comparable to the balance of living nature as a whole, such that any 

 disturbance of any one factor produces a disturbance in all the other factors. 

 This recalls to our memory one of Herbert Spencer's definitions of life, namely, 

 that life is a continuous adjustment of all internal relations to all external re- 

 lations. 



This coincides also with John Stuart Mill's doctrine of cause cited above as 



the "sum total of the conditions, positive and negative, taken together." This 

 conception of a multiplicity of conditions antecedent and consequent must be 

 in the mind of every biologist who seeks to determine the causes of the origins 

 and of the transformations of characters. 



This conception of inseparable relations has more than a theoretical, it has 

 a highly practical bearing in palaeontology and in experimental zoology. 



Granted that new characters as well as transformations of existing characters 

 must have origins or beginnings, in what part of the complexes of conditions do 

 they first appear? What is invariably antecedent, and what is invariably con- 

 sequent? Where is the initiation of the chain of conditions which leads to the 

 genesis of new characters? This is the question which the author set to himself 

 in the examination of every new character and of every transformation of char- 

 acter discovered among the fossil titanotheres. Was there evidence of a dis- 

 turbance in the balance of conditions and where did this disturbance originate? 



This method of analysis by which the answer shall be attained appears to 

 be the right one, but the answer itself is not yet. The first step is the recognition 

 of the universal law of the inseparable actions and reactions of the four factors, 

 a law which we propose to designate as Tetraplasy, from rfrpa (four) and 

 irxdcam (to form, mould, shape). 



After several years of reflection and analysis of the evolution of the titano- 

 theres, the author first presented this law in an address before the Department 

 of Zoology at Columbia University November 3, 1905. It was not published, 1 

 however, until after the Boston meeting of the Seventh International Zoological 

 Congress of August, 1907. In December, 1908, the subject was presented before 



1 Osborn, H. F.: Evolution as it Appears to the Paleontologist. Address before the Seventh 

 International Zoological Congress, Section of Palaeozoology, Boston, Aug., 1907. Science, N. S., vol. 

 XXVI, No. 674, Nov. 29, 1907, pp. 744-749. Proc. Seventh International Zool. Congr., Boston 

 Meeting, Aug. 19-24, 1907, Cambridge, Mass., 1912, pp. 733-739. The Four Inseparable Factors of 

 Evolution. Theory of their Distinct and Combined Action in the Transformation of the Titanotheres, 

 an Extinct Family of Hoofed Animals in the Order Perissodactyla. Science, N. EL, vol. XX VII, 

 No. 682, Jan. 24, 1908, pp. 148-150. Biological Conclusions Drawn from the Study of the Titano- 

 theres, Science, N. S., vol. XXXIII, No. 856, May 26, 1911, pp. 825-828. 



