still imperfectly understood. So far as we know, the 

 basic design of every micro-organism larger than a 

 virus is precisely as Von Neumann said it should be." 



This qualitative triumph was not the last of the mathematical 

 approaches. Perhaps the most sophisticated work which followed was 

 that of the seventies by the distinguished physical chemist, Manfred 

 Eigen. He and his colleagues have elaborated a carefully controlled 

 model of linked chemical reactions, which shows the possibility of 

 the steady increase of chemical complexity by various feedback 

 mechanisms entirely within their model domain of interdependent 

 reaction rates and yields: the explicit working out of the vague old 

 notion of autocatalysis. But it seems rather far from our concrete 

 problems, for it begins with a mechanism of reproduction with 

 interaction. Yet it is the origin of that mechanism which is a central 

 problem. 



Once again, the impact of this abstract work is, so far, stronger 

 at the level of general understanding than upon the actual search for 

 terrestrial beginnings; most workers prefer to take strong clues from 

 the specificity of the life we know than to follow logical conse- 

 quences of plausible general models. There are hints of experimental 

 systems: Certain bacterial cells, products of some error in cell divi- 

 sion, metabolically complete but without genetic apparatus, might 

 allow a kind of direct experiment in the domain of self-reproducing 

 automata. But most effort still seems directed to a more chemically 

 characterized level. 1 For most work so far, that has been the pursuit 

 of a bridge across the present wide gulf between the stable nucleotide 

 memory string — the DNA — and the reactive peptides of enzymes, 

 the structural proteins, and perhaps some other membrane constitu- 

 ents. The emergence of a self-reproducing system from single mole- 

 cules is yet elusive. 



LIFE ON A TAPE 



Perhaps the most important achievement of modern biology has 

 been the discovery of the chemical structures and mechanisms 



1 Important representative chemicals are illustrated in the appendix. 



