A COMMENTARY ON LAMARCKISM 



microcosm — these variants stand at no selective advantage; 

 but under the influence of penicilHn they proliferate more 

 rapidly than their unresistant neighbours and so eventually 

 become the prevailing forms. 



The second is illustrated by Fig. 5. It is presumed that the 

 enzymic organization responsible for the metabolic activity of 



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Fig. 5. The development of penicillin-resistance in 

 bacteria, according to a Lamarckian interpretation. 

 For expanation see text. 



each individual is progressively altered, as the shading indi- 

 cates, and that the change so produced is heritable. The change 

 in the properties of the population is therefore the sum of the 

 changes brought about within each individual. The difference 

 between the two interpretations, Darwinian and Lamarckian, 

 is that the one presents adaptation as a change in the genetical 

 structure of a population, and the other as a change in the 

 genetical structure of an individual. These are avowedly ex- 

 tremes, for they are in no sense mutually exclusive. On the 

 contrary, any inherited difference in the 'Lamarckian'' adapt 

 ability of individuals must of necessity become the subject of 

 selective discrimination. 



So much is commonplace. Let us now consider not a single 

 population but an assembly of such populations, supposing 

 each one to be anatomically separate and distinct. The entire 



F 81 



