INTRODUCTION 



Mutation and adaptation. — The problem of organic adaptation in bacteria 

 has been resolved into two points of view which are closely analogous to "neo 

 Darwinian" and "Lamarckian" concepts of organic evolution, respectively. 

 The first holds that adaptive changes occur spontaneously, as sporadic mutations, 

 not in any specific relationship to environmental conditions, and that natural 

 selection functions to fix the best adapted genotypes. The Lamarckian viewpoint 

 suggests that the adaptive mutation is itself directed by the environment, and 

 that natural selection plays a subsidiary role. Many of the papers reprinted 

 show experiments which support the spontaneous mutation hypothesis ( i, 3, 5) . 

 One (6) deals with the end result of bacterial adaptation to Chloromycetin 

 and also argues for spontaneous mutations with accumulative effect by 

 separating the components by recombination. There is no representative here 

 of the alternative point of view which is defended strongly by Hinshelwood and 

 his associates (28, 67, 70). In considering this problem it is essential to keep 

 in mind physiological adaptations which are nonheritable, but whose interplay 

 with heritable changes may trap the unwary (97, 120, 45-Lwoff). General 

 discussions of this problem are included in most of the review articles (32, 54, 

 81, 82, 87, isi, 129). 



Mutations for resistance to bacteriophage had been considered some years 

 before Luria and Delbriick's paper (1), notably by Burnet (34). This author 

 drew the same conclusions concerning the spontaneity of the resistance muta- 

 tions, mainly through his ability to pick out resistant mutants by their colonial 

 morphology without the use of phage as a selective agent. Much of the current 

 work on E. coli phages (43, 44, 21) involves a set of 7 virus strains described 

 as Ti through T7. Mutation rates for resistance to these phages have been 

 recorded, together with useful information on cross-resistance patterns (48). 



The physiological study of mutant characters is known as phenogenetics, 

 in contrast to formal or cryptogenetics which deals directly with the mechanism 

 of hereditary transmission. One would reasonably expect that a gene mutation 

 would require a period of time to work its effects on the phenotype or outward 

 behavior of the organism. This lag in bacterial mutation effects (phenotypic 

 or phenomic lag) was first noticed directly with phage-resistance mutations 



The citations in the Introduction refer to the Bibliography, pp. 299-303. 



