408 V. THE NATURE OF EVOLUTION 



development, but there is no doubt that the evolution is quite possible 

 without selection. 



Every character of organisms is wonderfully fitted for the purpose 

 of their existence. Since the character to achieve the evolution must 

 be of the most importance for the organism, extensive advancement 

 should be expected also in this character. In addition, since the char- 

 acter must be advanced with the progress of the evolution, it must be 

 the more advanced, the higher the organimsms are evolved. 



Nevertheless, at present the majority of authors seem to believe 

 that the organic evolution war. advanced mainly by virtue of random 

 mutation and natural selection, a wonderfully clumsy means which 

 might only be adopted by extremely primitive organisms as mentioned 

 in the next section. 



2. The Evolution of Evolution Mechanism 



New protein molecules are considered to be syntheszied as replicas 

 of the template protein constituting the protoplasm or assimilase, but 

 the newly formed replicas may not be precisely identical to the tem- 

 plate because of partial failure of the replication, thus arising the 

 individual differences in the structure of protein molecules. Such an 

 individual difference of the structure may in turn give rise to the 

 difference in the behaviour of each protein molecule or each polymerized 

 product of molecules towards the environmental factor, and accordinly 

 each may tend to undergo each peculiar change or mutation. Vari- 

 ations of primitive organisms might be thus raised and become distinct. 

 An individual having a structure tending to be changed in a definite 

 direction under the effect of a certain environmental factor might 

 continue to be changed in its structure in the direction under the 

 influence of the factor. 



Among the individauls thus coming to have different structures, 

 only those most fitted to exist would be able to survive, that is, the 

 fittest would be selected by natural selection. As a result of this 

 selection, the faculty to evolve spontaneously into a well adapted 

 direction might be gradually advanced. 



Although the protein itself possesses the basic character to adapt 

 itself to environments as already stated, the character might be insignifi- 

 cant when it was not yet developed enough, and presumably random 

 mutation and selection might play a predominant part in the evolution 

 of protein molecules. 



The evolution brought about thus mainly by mutation and selection 

 might continue until the proteins were polymerized into complete forrru 



