Xll 



act of code reproduction itself. These complex molecules are univer- 

 sal in life forms today; they have long seemed a wise starting point 

 for the search for origins. 



Neither a coded message, whose slow elaboration is the only 

 key to the evolutionary path, nor these protein jigs and fixtures, 

 which alone allow the expression of the inert code within the world 

 of living change, can be the whole story. No code, no way to elabor- 

 ate the chain of life forever; but no jigs, no action on the world. A 

 biological contract between these molecules, or more strictly, 

 between these two functions in some molecular form, seems the 

 center of the issue. We do not see it clearly yet. The clues from pres- 

 ent life are useful, but today the mechanism has become so precise, 

 so well-functioning, so long-elaborated that the steps that led to it 

 from a simpler, nonliving world are hard to guess. It is possible that 

 some simplified intermediate structures will be found; it is also possi- 

 ble that some key contrivance, now entirely superseded, must be 

 found. Some think that the inorganic substructure of some mineral 

 might have offered a crystalline framework for the first systems of 

 molecular self-reproduction. Other essentials besides the message and 

 the action are postulated; or perhaps some early form of the 

 message may have been at least weakly self-acting. The whole topic is 

 complex, central, challenging. 



One conclusion seems stronger than ever, touching on the eons 

 of evolutionary elaboration. It seems likely that the first cells of the 

 microbial mat were the unusually small and structurally more or 

 less simple ones which still distinguish the bacteria and the blue- 

 green algae as a group from all other higher forms of life. Sometime 

 in the first 2 b.y., new cell types arose. More or less algal, they were 

 big, hundreds of times the volume of their forebears, like most cells 

 of the animals and plants of today. Moreover, they held the special- 

 ized organelles of cells, those which today carry out efficient photo- 

 synthesis, hold and take out the message molecules safely and pre- 

 cisely, arrange for sequential reactions of energy storage and 

 liberation, etc., in all higher forms. The smaller cells perform the 

 same functions (indeed, as biochemists they are even more versatile), 

 but they lack many advantages of rate and of diversity in reproduc- 

 tion. There is good reason to believe that here we see another later 

 social contract — the organelles of the larger cells are perhaps the 

 offspring of once-independent organisms, which long ago contracted 



