Basic to this evolution is the mechanism — itself slowly perfected by 

 mutation and natural selection — that brings about the nearly flaw- 

 less replication of DNA and its mutants, and through them, of pro- 

 teins and the entire organism. 



The spontaneous origin of so complex a system as that 

 described above poses great conceptual difficulties. It must be recog- 

 nized that the simplest modern genetic system we see is highly 

 evolved; the original system was probably much simpler. Two logi- 

 cally possible predecessors are worth exploring: (1) polynucleotides 

 which still retain some catalytic capability, and (2) polypeptides 

 which yet have some replicative capability. Molecular systems such 

 as these would be extremely inefficient by standards of life today, 

 but they might have been sufficiently accurate under the less- 

 competitive conditions of the primordial Earth to survive and to 

 evolve. Either one might have been capable of developing into the 

 modern dual mechanism. 



THE LOCALIZATION OF ORDER 



The search for interactions among molecules which might lead 

 to self-replicating systems of either or both kinds of molecules, 

 nucleic acids and proteins, has progressed to some depth. Biochemi- 

 cal preparations which are essentially homogeneous solutions can 

 yield remarkable results whenever the polymer prototypes required 

 are present in rather high concentration. The classical experiments on 

 DNA replication in vitro are only one famous example. 



But this sort of system is not without its limitations. It is after 

 all the cell, a large set of interactive molecules, which is the unit of 

 present-day life. The notion that simple mutations — if one thinks of 

 many successive single-point modifications within a long polynucleo- 

 tide sequence — could in the fullness of time lead to the marvelous 

 outcomes of natural selection is inherent in the point of view. Surely, 

 that is too simple a view of the actual course of evolution. The time 

 required for a given selective result can be much reduced if the pro- 

 cess proceeded among quite distinct strings of genes, to join several 

 of them later in an action which may confer complex, new capabili- 

 ties all at once. This is of course seen in living forms at many genetic 



