512 



( IIAI' I I K 42 



action oi glyceraldehyde, acetaldehyde. am- 

 monia, oxaloacetic acid, glycine, and t'ormyl 

 residues. 



Molecular evolution leads not only to 

 greater complexity but to greater stability 

 of molecules. Accordingly, separate pro- 

 tein and polynucleotide chains might join 

 to form a more stable complex. (We know 

 that a DNA-histone complex stabilizes 

 DNA; double-strandedness and polynemy 

 could also be nucleic acid stabilizing fac- 

 tors.) The final protein-nucleic acid com- 

 plex, however, need not have started with 

 a protein or a polynucleotide. Single nu- 

 cleotide-single amino acid units might have 

 occurred which polymerized to form a poly- 

 peptide first and a polynucleotide later or 

 the reverse. Regardless of the manner in 

 which the nucleic acid-protein complex 

 evolved, such a complex must already have 

 entailed a primitive code by which nucleo- 

 tides and amino acids code for each other. 

 Since nucleic acids make better templates 

 for replication than proteins, the nucleic 

 acid portion of a nucleoprotein became ge- 

 netic material. As chemical evolution pro- 

 ceeded, the number of nucleotides specify- 

 ing a single amino acid could have increased 

 from one to the three — the size of our pres- 

 ent codon. 



Even if the evolution of proteins and pol- 

 ynucleotides was independent for some time, 

 it seems clear that the two substances be- 

 came interdependent in their later evolution. 

 In view of the relative chemical inactivity 

 of nucleic acids, we may hypothesize that 

 one primary result of their evolution was 

 the stabilization of enormous numbers of 

 protein molecules and protein cycles which 

 arose in Era III; a second primary re- 

 sult of nucleic acid evolution led to pro- 

 tein replication by ribonucleic acid. In 

 other words, chemical evolution seems to 

 have been largely a matter of protein evo- 

 lution during which nucleic acids came to 



serve as stabilizers of and templates for pro- 

 tein synthesis. Such an evolution would be 

 expected it nucleic acids were first formed 

 in an environment whose organic compo- 

 nents were largely protein. Since nucleic 

 acids do not include Sulfur (and many other 

 elements) in their basic makeup, they lack 

 the proteins' chemical drive for stability. 

 The stabilization of proteins was probably 

 further enhanced by retaining the infor- 

 mation in DNA, rather than RNA whose 

 use became more and more restricted to 

 the translation process. As the nucleic 

 acid transcription and translation processes 

 evolved, it surely became advantageous to 

 step up the rate of these reactions through 

 the use of nucleic acid polymerizing en- 

 zymes. It also became advantageous to 

 protect nucleic acids from peroxides formed 

 in the environment by radiation. Thus, it 

 is likely that the nucleic acids which en- 

 coded catalase protected the nucleic acid 

 directly and protein synthesis indirectly. 

 Since prebiotic and biotic chemo-evolution 

 is largely describable in terms of protein 

 structure and function, the present view — 

 that genetic nucleic acids played a lesser 

 role — is already generally accepted and not 

 at all novel. The subservient role of nu- 

 cleic acids is generally evidenced in present 

 day organisms not only in the requirement 

 of GPP in protein synthesis and of APP for 

 the transport of energy, but also of UPP 

 and CPP for the transport of monomers in 

 the synthesis of carbohydrates and lipids.' 1 

 Because of the intimate relationship be- 

 tween amino acids and genetic material, we 

 need to learn more about the evolution of 

 all kinds of organic compounds, especially 

 energy-rich compounds (such as ATP), cat- 

 alysts (such as iron-containing compounds), 

 and energy-capturing compounds (such as 

 chlorophyll). 



"See R. E. Eakin (1963). 



