The Evolution of Chemosynthesis 627 



his book on the origin of life and by Omelyanskii [9] in his manual of micro- 

 biology. All these investigators considered the autotrophic type of metabolism 

 to be more ancient than the heterotrophic one. Similar views are to be found 

 even in quite recent pubhcations. Thus Rabinowitch [10] in his book Photo- 

 synthesis holds the opinion that chemoautotrophic bacteria are of primary origin. 

 He beheves that organic molecules, originating under the influence of ultra- 

 violet rays or electric discharges, gave rise, in some way or other, to chemo- 

 synthetic organisms. These, in the author's opinion, utihzed for chemosynthesis 

 the energy of oxidation of free hydrogen or hydrogen sulphide present in the 

 atmosphere at that time. Later, according to Rabinowitch, the evolutionary 

 development of chemosynthetic microbes led to the appearance of purple 

 bacteria, and further on of green plants which had come into being earUer than 

 heterotrophic bacteria. 



Kermack & Lees [11] assert that chemoautotrophic bacteria, as organisms less 

 exacting with regard to the nutrient substrate, are, in the evolutionary aspect, 

 of more ancient origin than heterotrophic bacteria, the nutritional requirements 

 of the latter being more complex than those of autotrophic bacteria. The above- 

 mentioned authors founded their reasonings on the theory of evolution of 

 physiological functions put forward by Lvoff [12]. According to Lvoff, the 

 evolution of physiological functions proceeded not by their becoming more 

 comphcated, but through a gradual limitation of the organism's capacity for the 

 synthesis of complex substances out of simple compounds. This resulted in a 

 complication and specialization of their food requirements. From the standpoint 

 of this theory, it naturally follows that autotrophic bacteria must have been the 

 primordial organisms. The inadequacy of such an anti-evolutionary 'theory of 

 evolution', and of the conclusions derived on its basis, is quite evident. 



In a recently pubHshed monograph on the biochemistry of autotrophic bac- 

 teria Lees [13] again suggests that primordial organisms did not require ready 

 organic matter. In his opinion, these primary organisms might have been 

 organisms of the type of pigmented photosynthesizing sulphur bacteria. Accord- 

 ing to Lees, chemosynthetic microbes originated from photoautotrophic bacteria 

 through the loss by the latter of their photoactivating pigments. He beheves that 

 it was sufficient for the primary organisms to possess a few enzymes to be capable 

 of utiHzing the energy of Ught for assimilating CO2. It is well known, however, 

 that the capturing of light energy, its transformation into chemical energy, the 

 formation of reducing agents and, finally, the fixation of CO2 and its reduction 

 to organic matter are carried on in contemporary photoautotrophic organisms by 

 means of very elaborate biochemical mechanisms. The enzyme systems and 

 mechanisms of heterotrophic metabohsm form the basis of all these processes. 



Before the complex mechanisms of autotrophic nutrition appeared, the pri- 

 mordial hving beings had doubdess passed a long period of evolution and gradual 

 increase in complexity on the basis of simpler metabolic reactions, utiUzing ready 

 organic matter. 



Another, more thoroughly substantiated viewpoint regarding the evolution of 

 chemosynthesis has been set forth by A. I. Oparin [14]. According to Oparin, 

 chemoautotrophic bacteria originated from heterotrophic forms, they appeared 



