A COMMENTARY ON LAMARCKISM 



course. But as matters stand at present, the interpretation of 

 Hraining"* adaptations is highly controversial, the controversy 

 being between those who maintain that training is secured both 

 by population selection and by heritable transformations of 

 individual cells, and those who maintain that only the former 

 mechanism is at work. 



It may be said at once that numerous studies of the highest 

 exactitude have made it clear that the differential survival of 

 genetic variants is a ubiquitous property of populations of 

 micro-organisms, and the truth of this proposition is not 

 therefore in dispute. At the same time, the prolonged and 

 exact experiments of Hinshelwood (1946; cf. also Baskett and 

 Hinshelwood, 1951), expressly designed to discriminate be- 

 tween selection and adaptation, show that the adaptive trans- 

 formation of individual cells could well be a capital factor 

 in the training responses of bacterial populations.* The two 

 mechanisms are no more incompatible in bacteria than in 

 Paramecia; indeed, there is a formal analogy between antigenic 

 transformations in the latter and training responses in the 

 former. For example, Kilkenny and Hinshelwood (1951) have 

 compared the adaptation of three strains of the yeast Saccharo- 

 myces cerevisiae to the use of galactose: one adapted itself 

 promptly, a second slowly and the third not at all. These diifer- 

 ences of adaptive potential were inherited according to the 

 ordinary rules of Mendelian segregation, but within each strain 

 adaptation, if it occurred, was brought about by transforma- 

 tions of individual cells. 



Hinshelwood, it may be noted, has more than once insisted 

 that any differences of adaptive capacity between individuals 

 are bound to be inflated by selective forces, and the com- 

 patibility of 'adaptive** and ""selective' explanations may be 

 illustrated by reference to Paramecia. If Paramecia of mixed 



* [Many later experiments by Hinshelwood 's school have been published 

 in Series A of the Proceedings of the Royal Society.^ 



103 



