288 ORIGIN OF STRUCTURES AND FUNCTIONS 



nucleic acid. Nucleic acid, reproducing itself and forming 

 proteins in conjunction with the metabolism of the ocean 

 itself, also constitutes, according to Roka, 'living protoplasm'. 

 By degrees more and more ' living protoplasm ' ^vas formed 

 while the surrounding medium became more and more ' life- 

 less ' until eventually the process culminated in the formation 

 of the first organisms. 



This schematic description is, however, open to a number 

 of objections. In the first place, it is hard to imagine the 

 development of metabolism simply within the aqueous solu- 

 tion of the primaeval ocean. Metabolism is not merely the 

 conjunction of various reactions co-ordinated to some extent 

 in time. In organisms of the present day, metabolism is a 

 definite organisation of processes directed to^vards the con- 

 tinuous self-preservation and self-reproduction of the living 

 system as a whole. Such an organisation could only have 

 been built up by natural selection and selection requires 

 circumscribed individual formations and could not take 

 place in a homogeneous solution. This is the first point ; the 

 second is that although Roka's outline, which we have 

 discussed in Chapter V, demonstrating the possibility that 

 polynucleotides may be formed by the transformation of 

 polyphosphoric acids seems very probable and apposite it 

 still does not solve the question of the origin of nucleic acid 

 itself. This latter is distinguished from simple polynucleo- 

 tides in that the arrangement of the mononucleotides in its 

 chain is strictly determined and its biological role in the 

 synthesis of proteins depends on its three-dimensional intra- 

 molecular structure. This is, of course, the very property 

 which requires explanation and Roka passes it over in silence. 

 Reference to the ' happy chance ' that, out of many billions 

 and quadrillions of combinations there could have been 

 formed by chance just that indispensable sequence which is 

 required for the synthesis of proteins is just as irrational in 

 this case as were earlier references to the ' chance ' formation 

 of proteins (enzymes). Not only is the structure of these 

 proteins very complicated but it is extremely thoroughly 

 adapted to the performance of definite catalytic functions 

 which play an important part in the life of the ^vhole organ- 

 ism, it is inwardly ' constructed for its purpose '. Such 



