2'72 THE FIRST ORGANISMS 



take in from the surrounding medium the porphyrins which 

 were formed there by purely abiogenic means, just as some 

 contemporary organisms extract from their environment 

 vitamins which they need for the synthesis of enzymes. On 

 combining with the iron, the porphyrin would markedly 

 increase its catalytic activity, and if such a speeding up of 

 the reaction under discussion was favourable to the dynamic 

 stability of the drops in which it occurred, then these drops 

 would enjoy a considerable advantage in the process of selec- 

 tion compared with other similar systems. Thus the drops 

 which were preserved for further evolution would be just 

 those which had a structure enabling them to adsorb por- 

 phyrins selectively. 



Analogous considerations also apply to the formation of 

 other specific catalysts and enzymes. Even such compara- 

 tively simple substances as, for example, methylamine, 

 glycine, aldehydes, sugars, etc., have a weak catalytic activity 

 for some reactions. These compounds could enter into the 

 original systems or even, to some extent, be synthesised there. 

 In the various coacervate drops they could combine with one 

 another and with the inorganic catalysts present there in 

 hundreds and thousands of different ways. Among all these 

 combinations there must certainly have been some in which 

 the catalytic activity was greatly increased owing to a favour- 

 able disposition of active and activating gi'oups. A particular 

 case might be the successful combination of amino acid 

 residues in the polypeptide chains of the protein-like sub- 

 stances. This might give marked advantages to the systems 

 in which there were formed combinations which had a 

 powerful catalytic activity favourable to their dynamic stabil- 

 ity and general activity. 



This internal chemical rationalisation of the systems was 

 reinforced by their selection. This destroyed those in which 

 there had arisen, by chance, ' unsticcessful ' combinations 

 which diminished the catalytic activity. It preserved for 

 further evolution only the more efficient catalysts which were 

 more capable of performing their functions. 



