The Problem of Stages in Biopoesis 37 



oxidation mechanisms, leading to a hydrogen shortage which was only relieved 

 by the evolution of a means of extracting it from water with an improved chloro- 

 phyll photocatalyst. Only after this stage had been reached and oxygen began to 

 accumulate in the atmosphere did its pressure rise sufficiently to initiate the more 

 comphcated oxidative processes supplementing those of fermentation. Some 

 oxidations of the sulphide to sulphur type may have preceded this stage, but the 

 energy gain would have been much lower. In the overall picture of the evolu- 

 tion of the chemistry of Ufe what we notice is not so much an improvement in 

 the total energy changes — except in so far as solar energy is used — but rather in 

 the effecting of a speedier turnover, in increase in power of assimilation or 

 energy production. 



With the other element in catalysis, the specific fixed base, similar considera- 

 tions apply. It is clear that the present profusion of protein enzymes cannot have 

 been primitive. A major problem is the discovery of what preceded them in this 

 role. The degree of polymerization of amino acids and the complexity of their 

 sequences which would be required before a protein could function as an 

 enzyme is very great. Protein enz}Tnes must therefore have come relatively late 

 in biopoesis. What preceded them ? Even simpler amino acid polymers cannot 

 have been primitive and it would appear that the choice lies between postulating 

 an inorganic crystal-clay or quartz as the primary catalyst or assimiing that in 

 the early stages there was no heterocatalysis and that reactions proceeded through 

 the diffusion of active radicals as Pringle [i] has proposed. 



The discussion of the first stages of biopoesis, the formation of what Pirie [2] 

 has called probiotic soups, involves not only the chemical problems of the 

 formation of the particular organic molecules they contained and of the reaction 

 chains that link them, but also the physico-chemical problem of how these 

 molecular concentrations were built up and maintained. It is conceivable, though 

 I think unlikely, that no such stage of solution of monomers or oligomers such 

 as amino acids, simple peptides, or sugar molecules, ever existed and the forma- 

 tion of such molecules went pari passu with their polymerization. If, however, 

 free molecules ever existed or even more so, if there was a stage where these 

 were the only molecules there were, the problem of how their diffusion was 

 restricted is a real one that bears closely on the locus of the origin of life. All 

 conditions counter-indicate the primary synthesis of anjnihing but the very 

 simple molecules, of say three to six atoms, in large volumes of water where the 

 dilution is so great that the probability of chance encounters leading to more 

 complex compounds would be negligible. The possibHities of small volumes of 

 water such as occur in drying pools are rather greater as far as concentration go, 

 but not the maintenance and propagation of the resulting substances and re- 

 actions, for the chances of drying up or washing out would be too great. 



What is required is a mediimi free from turbulence and imder constant 

 conditions for long periods in which the diffusion of small molecules, though 

 never stopped, would be so restricted that considerable concentrations could be 

 built up and maintained. Such conditions are only likely to be found on an 

 azoic Earth — in mud beds; under water; on dry land; or alternatively wet and 

 dry as in tidal estuaries. From the purely physical point of view it is unimportant 



