Evolution.

Society for Experimental Biology

Date:: 1953

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

Credit: Evolution. Source: Wellcome Collection.

37/484 (page 13)

$THE ORIGIN OF LIFE 13 equation leads to an exponential increase or to a stable equilibrium for X according as k' is greater or less than k{v— i), and to explain the whole course of the reaction it is necessary to postulate a change in these constants as the reaction proceeds. By a small change in the equation, however, ^=V„ + k{v-i)x-k'x\ (4) it becomes possible to interpret the whole course of reaction, and the analogy with biological equilibria is emphasized by the similarity of this to the logistic equation (i). In chemical terms equation (4) demands a bimolecular destruction process for the active intermediate and is quite consistent with what is known about chain reactions in general. It is at least highly suggestive that this type of behaviour is shown by oxidative reactions which are the source of energy for the living organism, and that the substrates required are just those which have been postulated by the detailed chemical schemes of Oparin (1938). Oparin gives cogent reasons for supposing that carbon first appeared in molecular combination in reduced form, as carbides of the metals yielding a variety of hydro¬ carbons under the action of steam, and that these were slowly oxidized due to the loss of hydrogen from the atmosphere and to the dissociation of water in the upper atmosphere by ultra-violet light liberating small amounts of oxygen and hydrogen peroxide into the circulation. In the presence of ferrous salts from the lithosphère it is to be expected that free radicals such as OH and HOg will have been present to start reaction chains even at depths to which no solar radiation penetrated. Doubt about the probable degree of absorption of ultra-violet light in an atmosphere from which it can liberate ozone makes Haldane's (1929) alternative theory of the direct production of simpler organic compounds even less attractive in the light of this demonstration of the possibility of a ' biological ' type of equilibrium at such an early chemical stage. But there is another and even more cogent reason for demanding this type of equilibrium at the very start of organic synthesis. It is possible to think of free radicals whether produced by radiation or in chain reactions condensing with ammonia, sulphide and other inorganic molecules to give a wide range of organic substances in extreme dilution, but, as both Oparin and Bemal have pointed out, ' the concentration of products is an absolute essential for any further evolution' (Bernal, 1949). Oparin is not able to suggest any mechanism which might produce such concentration before the colloidal stage is reached, when he suggests that coazervation may have been responsible for the appearance of the primitive organism. Bernal helps to bridge the gap with the aid of particles of clay and other hydrated$

Evolution.

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