The Origin and Evolution of Genetic Material 



511 



the energy sources were primarily respon- 

 sible, there cannot be any doubt that syn- 

 thesis and accumulation of a great variety 

 of organic molecules took place in the 

 oceans, making an "organic soup. ,, During 

 this era, whose length has not been estab- 

 lished, most of the free hydrogen escaped 

 from the earth's atmosphere. 



Era II. Its atmosphere was also a re- 

 ducing one with only traces of free oxygen. 

 Initially, the same energy sources were 

 available for chemosynthesis in this era as 

 in Era I. As traces of oxygen escaped to 

 the atmosphere, ultraviolet rays from the 

 sun converted the oxygen into ozone. Since 

 ozone absorbs ultraviolet light, the ozone 

 layer in the atmosphere acted as a blanket 

 so that the main chemosynthetic energy 

 from the sun was visible light and heat. 



A study of the comparative biochemistry 

 of present higher plants and animals, bac- 

 teria, and many viruses, shows that all are 

 intimately associated with the same 20 or 

 so amino acids. Accordingly, protein and 

 nucleic acid are, perhaps, the most durable 

 chemical features of the earth, having ex- 

 isted for more than a billion years. In the 

 presence of excess aspartic acid and glu- 

 tamic acid, temperatures of 200°C or less 

 can be used 3 in a dry heat synthesis to pol- 

 ymerize amino acids into proteinoids, poly- 

 mers containing, in peptide linkage, all or 

 most of the amino acids common to pro- 

 teins. Proteinoids are linear polymers with 

 a molecular weight of up to 10,000, show 

 weak catalytic activity, and, for the most 

 part, are indistinguishable from natural pro- 

 teins or polypeptides of similar size. Al- 

 though proteinoids are nonantigenic, in hot 

 water they tend to form spheres about two 

 microns in diameter. Since the spheres 

 swell and shrink as the sodium chloride con- 

 centration of the medium is changed, we are 

 reminded of osmotic behavior. Sometimes 



3 See S. W. Fox (1960, 1964). 



such microspheres undergo a kind of fission 

 and show a double-layered outer membrane 

 in electron micrographs. Homopolymers 

 and copolymers of certain amino acids can 

 also be produced by dry heat. 



On the basis of such evidence and rea- 

 soning, it is expected that during Era II 

 complex organic substances were synthe- 

 sized — polypeptides, nucleotides, carotenes, 

 polyphosphates, pigments, and porphyrins. 

 It is also expected that adsorption and prim- 

 itive catalysis occurred involving surfaces of 

 clays and or polypeptides. 



Era III. This era is assumed to be 

 mainly anaerobic with only trace amounts 

 of free oxygen and some carbon dioxide. 

 It is suggested that during this period syn- 

 thetic cycles evolved (as did specific catal- 

 ysis and photochemistry) on the surfaces of 

 large organic molecules. As the last evo- 

 lutionary step of this era, primitive enzymes 

 and genes also arose, leading to the first or- 

 ganism. 



Some recent research and speculation 4 

 may throw more light upon the evolution 

 and interdependence of polynucleotides and 

 proteins. As mentioned, it is likely that 

 proteins and mononucleotides were already 

 present at the start of Era III. In the pres- 

 ence of dehydrating agents, water is re- 

 moved and nucleotides are joined to form 

 polynucleotides with molecular weights of 

 up to fifty thousand. Note that such a pol- 

 ymer is made without the use of an enzyme. 

 The rate of such a nonenzymatic synthesis 

 of polyuridylic acid has been found 5 to in- 

 crease more than tenfold in the presence of 

 polyadenylic acid, which suggests that the 

 latter homopolymer can serve as a template 

 during the nonenzymatic synthesis of the for- 

 mer homopolymer. A hypothetical scheme 

 has been proposed to form DNA by the re- 



4 See article by A. Rich in M. Kasha and B. Pull- 

 man (1962). 



5 By G. Schramm. H. Grotsch. and W. Pollmann 

 (1961). 



