Conclusions and Theoretical 243 



range of reactions from simple autocatalytic reactions which may 

 direct the chemical evolution of intracellular metabohtes, to self- 

 contained autotrophic organisms. The position of the gene in this 

 hierarchy is not established." He stresses that an experimental proof 

 for self-dependence of a visible particle is very diflBcult, requiring (as 

 with nuclear genie material) a complete paralleHsm in the distribution 

 of the particle with the effects of the plasmids ( a term he prefers to 

 plasmagenes ) . Also the capacity for mutation is not necessarily a 

 criterion; it may be only the expression of structural complexity, re- 

 arrangements of the pattern being interpreted as mutations of the 

 complex. (See our discussion of mutation as pattern change given 

 previously. ) 



In making the step from the assumed "plasmids" to viruses and 

 symbionts, Lederberg cautions that the properties of plasmagenes may 

 be imputed readily to viruses and vice versa. He thinks attention 

 should be focused on plasmid functions which may change from adap- 

 tive to pathological . . . "Present evidence points to the nucleus as 

 the predominant, if not quite exclusive, seat of hereditary factors in 

 most organisms . . . However, we learn less, not more, if we exclude 

 extranuclear agents as hereditary factors because they may also 

 simulate symbionts or parasites; such behavior is important but 

 incidental to their genetic functions. The cell or the organism is not 

 readily delimited in the presence of plasmids whose coordination may 

 grade from the plasmagenes to frank parasites . . . How then shall 

 we choose the boundaries of the gene-complex that constitutes an 

 individual organism? If hierarchical definitions are to serve the scien- 

 tist, rather than the scientist serve an Aristotelian category, different 

 uses should dictate different usages. The geneticist may well choose 

 that entity whose reproduction is unified and, hence, functions as an 

 individual in evolution by natural selection. The microbiologist will 

 focus his interest on the smallest units he can separate and cultivate 

 in controlled experiments, in test tubes, eggs, bacteria or experimental 

 animals. Genetics, symbiontology and virology have a common meet- 

 ing place within the cell. There is much to be gained by any com- 

 munication between them which leads to the diffusion of their 

 methodologies and the obliteration of semantic barriers." Our former 

 discussion indicates how far I am able to follow this attitude and 

 where our ways are parting at present. 



I have refrained thus far from more than mentioning the idea 

 that viruses are directly comparable to genes and that there is a 

 complete series of transitions from virus to plasmagene to nuclear 



