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what extent and in what ways (if any) is the eucaryotic cell poly- 

 phyletic in origin? More broadly, to what extent is it chimeric? How 

 many (and what) major lines of eucaryotes are there? (In other 

 words, how many kingdoms lie hidden in the general classification 

 protista?) This question is underlain by the important general one of 

 how easily various major states in evolution are arrived at. The wide 

 range of questions raised points to a future growth of knowledge in 

 this area. The origin of the cell may lay hidden in the biological 

 record. 



To quote the biochemist, Szent-Gyorgyi: "Life has developed 

 its processes gradually, never rejecting what it has built, but building 

 over what has already taken place. As a result the cell resembles the 

 site of an archeological excavation with the successive strata on top 

 of one another, the oldest one the deepest. The older a process, the 

 more basic a role it plays and the stronger it will be anchored, the 

 newest processes being dispensed with most easily." 



CHEMICAL EVOLUTION 



As we have pointed out in chapter V, the field of chemical evo- 

 lution has been guided by the premise that the primitive atmosphere 

 was hydrogen-rich, a reducing atmosphere with the major forms of 

 carbon and nitrogen being methane and ammonia. However, recent 

 models of the Earth's early atmosphere have placed severe limitations 

 on the amount of hydrogen originally present. Since such a primitive 

 atmosphere would be dominated by carbon dioxide and nitrogen, the 

 capability of this atmosphere to sustain synthesis of amino acids and 

 other biomonomers might be limited. The possibility that there was 

 no soup of any complexity must therefore be considered and 

 explored experimentally. 



Thus, the field of the synthesis of biomonomers must be 

 broadened to encompass not only experiments as they have been 

 classically conceived (i.e., in the reducing atmosphere of the Miller- 

 Urey model) but also, experiments utilizing nonreducing gases (i.e., 

 CO, C0 2 , N 2 , etc.), minerals, and light. To the above must be added 

 the constraints imposed by our expanding knowledge of the early 

 Earth. 



