Evolution.

Society for Experimental Biology

Date:: 1953

Catalogue details

Licence: Attribution-NonCommercial-NoDerivatives 4.0 International (CC BY-NC-ND 4.0)

Credit: Evolution. Source: Wellcome Collection.

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THE ORIGIN OF LIFE I9 which appears to have as its 'objective' the direction of available energy into useful channels. We may suppose, then, on the principle that the evolution of the biochemical machinery of the cell took place under conditions not very dissimilar to those now found in the intracellular environment, that the process of retention of the energy of free radicals within a molecular con¬ figuration began in the presence of phosphate ions. Perhaps, due to its specific catalysing action in certain hydrogen transfer reactions, phosphate ion from mineral deposits provided the initial stimulus for Turing's con¬ centration process, thereby ensuring that the high concentrations of free radicals occurred where there was also a higher concentration of phosphate. It seems that the environment must also, at a slightly later stage, have contained pyrimidine and purine bases, ribose sugars and amino-acids, at least when protein and nucleic acid synthesis began on an appreciable scale, and as to how these organic species came to be produced there is no hint. But it is possible that a considerable range of compounds might be obtained by the local concentration of free radicals in a solution also con¬ taining ammonia and phosphate, the concentration process being cumu¬ lative as more and more of the dissipation of oxidative energy occurred in particular places. To achieve a progressive change from simple to complex catalysts with the persistence of each more complex stage it is, of course, necessary that the autocatalytically increasing units compete successfully with existing ones for the available substrate and oxidizing agents. One can imagine, even at this stage, the principle of the survival of the fittest at work, or, alternatively, can look for an explanation in terms of the rate constants of the competing chemical reactions (e.g. the increasing efficiency of hydrogen peroxide decomposition in the series iron salts > haematin > catalase, Stern, 1941). The two approaches are equivalent and serve to emphasize again the link between biology and physical chemistry at these early stages in the origin of life. VIII. CONCLUSION This hypothetical scheme involving branching chain reactions appears to have definite advantages over the Haldane-Oparin-Bernal scheme which attributes the initial formation of organic compounds to the direct action of ultra-violet light. It is, first, a more fruitful concept, since it demands a smaller degree of improbability for the significant events, and it could therefore be tested experimentally. It avoids the difficulty over the depth of penetration of radiation to be expected in an atmosphere containing water vapour. It also substitutes a process which is continuous for one 2-2