H. EYRING AND F. H. JOHNSON ' 3 



while the contrary effect accompanies catalytic speed up of decomposition 

 reactions. 



In the confused mass of chemical reactions which had accumulated after 

 a billion or so years of chemical evolution, crude enzymes were taking 

 shape, only to break up again. The rudimentary precursors of ribonucleic 

 acids were likewise forming and disappearing. Even in the presence of 

 these fragments of modern molecules the primitive ribonucleic acid with 

 the help of the rudimentary enzymes tended to make replicas of itself. In 

 addition, the ribonucleic acid acting as a template facilitated and so sped 

 the formation of enzymes. As long as the self-replication of ribonucleic 

 acid was not sufficiently rapid to replace the parent template before it 

 disintegrated from the ever present destructive reactions, the concentra- 

 tion of ribonucleic acid remained at a low level. Since template concen- 

 trations remained at a modest level, molecular evolution proceeded at a 

 correspondingly modest pace. But this situation had within it the same 

 sort of instability which is present in explosive mixtures involving branch- 

 ing chains where conditions are operating, such as a temperature rise, to 

 increase branching up to the explosion point. The explosion comes when 

 conditions have progressed to the point where more than one free radical 

 is formed for each free radical disappearing. 



Now as the partially self-replicating ribonucleic acid grew longer and 

 more perfect, the point was finally reached such that with the available 

 enzymes the template could more than replace itself within its life span. 

 At this instant within the space of 10~^-^ sec. (the lifetime of the activated 

 complex in any chemical reaction) the world suddenly changed. The pools 

 of water greatly increased in their concentrations of ribonucleic acid until 

 they reached a new stationary level. The slow halting changes of ineffec- 

 tively catalyzed chemical evolution had now come to a close with the 

 explosive-like emergence of total self-replication of ribonucleic acid. This 

 change to a self-replicating world ushered in the era of biological evolu- 

 tion. The new era was characterized by intense chemical activity catalyzed 

 by the abundant enzymes synthesized on the self-replicating templates of 

 ribonucleic acid. These replicas, together with better adapted mutants, 

 sealed the fate of all possible competitors. The same catalytic powers of 

 enzymes which speed up the synthesis of the self-replicating templates 

 also speed up their destruction. This new chemical tempo immediately 

 cuts down the concentration by cannibalism of all poorly catalyzed com- 

 petitors such as the precursors of the optical isomer of the critical complex. 

 Consequently, as soon as any really efficient self-replicating optically ac- 

 tive template, which synthesizes its cooperating enzymes, goes critical in 

 the way outlined above, it slams the door on its competitors, and what 



