THE ORIGIN OF LIFE 



complex mixture called a coacervate. Such coacervates would adsorb 

 water on their surfaces to form a sort of membrane, which would thus 

 establish the beginnings of individuality. 



Autocatalytic Systems, Genes, and Viruses. These large, complex, 

 colloidal aggregates, the coacervates, continue to undergo random chemi- 

 cal reactions in the course of which still larger aggregates may be formed, 

 or the existing ones may be broken down. It is most probable that some 

 of the systems thus formed would be enzymatic in character, that is, they 

 would tend to increase, to catalyze, the rates of specific reactions. Many 

 enzymes catalyze the reactions of substances unrelated to the enzyme 

 itself. Thus lipase will break down fats to glycerine and long-chain acids, 

 or it will catalyze the synthesis of fats under appropriate conditions. But 

 there are catalysts known which, given a suitable substrate, tend to cause 

 the production of more of the catalyst itself. The duplication of the chro- 

 mosomes is an example par excellence. Such enzymes are said to be auto- 

 catalytic. If an autocatalytic substance were to be formed in the primor- 

 dial seas, it would be expected to increase in quantity at the expense of 

 those organic compounds which lack this property. And thus is the char- 

 acteristic of self-reproduction introduced. Compounds possessing this 

 property might well be regarded as free genes. We need only add the 

 characteristic of mutability, that is, the capacity for undergoing changes 

 which are reproduced without interfering with the autocatalytic proper- 

 ties of the molecule, and we have the most fundamental characteristics of 

 the hereditary units, the genes. Such a structure would be comparable to 

 a free-living virus, and it is probable that, like the viruses of today, these 

 primitive anlagen of life were nucleoproteins. These nucleoproteins would 

 utilize the complex organic compounds of their environment for the auto- 

 catalytic synthesis of more nucleoprotein, that is, for reproduction. Calvin 

 has shown that even in the pre-organismic stages, a sort of natural selec- 

 tion, based upon thermodynamic principles, favors the events described. 



Origin of Bacteria. As larger self-reproducing units were formed, mu- 

 tation might result in the different parts of each aggregate becoming 

 differentiated. Or the same result might be obtained by the coalescence 

 of originally different "genes." At this stage, the structure would resemble 

 some of the smallest known bacteria, and might properly be called an 

 organism. The organisms dealt with up to this point would have to be 

 completely heterotrophic, that is, dependent upon complex food materials 

 present in their environment, and "feeding" would occur only by absorp- 

 tion. The fact that viruses can metabolize and reproduce only within the 

 protoplasm of higher organisms indicates that they are also heterotrophic. 

 They can utilize proteins, starches, fats, and vitamins already present, but 

 they cannot synthesize these from amino acids, sugars, and other simpler 

 organic precursors. On the other hand, all of the undoubted organisms 

 are able to synthesize at least some of their required foods from simpler 

 compounds. Green plants can synthesize their required foods from the 

 elements. Animals cannot do this, but they can synthesize proteins from 

 amino acids, complex carbohydrates from sugars, and some of the vitamins 

 from simpler precursors. These syntheses are possible because the organ- 



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