Eigens paradox

In 1981, Manfred Eigen proposed that the first replicators would have had a greater chance of surviving if they had been housed in small compartments instead of being freely diffusing in a solution. This is because compartments have an individuality, and individuals are the units on which natural selection can operate. 

In practice, the compartment hypothesis is equivalent to saying that primitive RNAs were replicating themselves in the interior of microscopic vesicles, and that the membranes of those vesicles were also being replicated. All this requires a system of RNAs and lipids 

We conclude that the replication paradigm has not been able, so far, to account for chemical evolution, but could be valid for postchemical evolution, and this, it will be remembered, is also Dyson s hypothesis (metabolism first, replication second). Let us examine therefore the evolutionary potential of primitive vesicles containing RNAs that could behave both as genes and enzymes. 

The replication paradigm requires that protein enzymes were not present at the beginning, and RNA replication was therefore performed by ribozymes. Some RNAs can in fact behave as polymerases and replicases, but they are far less efficient than the corresponding protein enzymes, and the accuracy of their replications was necessarily very low. The experimental measures, obtained from interacting coupled nucleotides, have shown that without protein enzymes the replication error e cannot be less than 0.01, which means, from formula 5.1, that primitive RNAs could not have, as an order of magnitude, more than 100 nucleotides (Maynard Smith and Szathmary, 1995). 

A more accurate replication required protein enzymes, but the synthesis of these enzymes required a primitive translation apparatus, and therefore the presence of genes for such an apparatus. The smallest genome that is capable of coding for a replicase and a rudimentary translation apparatus is not known, but it has been estimated that a minimum of ten genes is necessary in order to keep translation errors within tolerable limits. The appearance of a primitive genome presents, however, two contrasting problems. 

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