A COMMENTARY ON LAMARCKISM 



become inherited character differences under conditions that 

 formally exclude the action of natural selection. It will be clear 

 from Section 3 that evidence of the occurrence of any such 

 transformation in metazoa is still wanting. We must conclude 

 that although what I have called 'Class B' adaptations might, 

 unlike so many others, have arisen in Lamarckian fashion, 

 there is no unambiguous evidence that they have done so. 



This answer is quite widely thought by laymen and ill- 

 informed zoologists to be shifty-eyed and evasive, and the 

 reason is not far to seek. It is believed, quite mistakenly, that 

 eligibility for a Lamarckian interpretation is in some way dis- 

 creditable to Darwinism. The truth is quite otherwise. The 

 developmental pre-emption of what would otherwise be ac- 

 quired character differences is, with most adaptations of Class 

 B, of conspicuous selective advantage. If it is an advantage to 

 have thickened soles at all, it will be particularly advantageous 

 to have them ready-made — ready for use the first time the foot 

 touches the ground. And what could be more biologically inept 

 than a state of affairs in which the several joints, only roughly 

 fashioned at birth, had to be ''run in'' to complete their par- 

 ticular articulation patterns during the lifetime of each 

 individual? In so far as the plausibility of a Darwinian argu- 

 ment turns upon the demonstration of conspicuous selective 

 advantages. Class B adaptations are as amenable to Darwinian 

 explanation as any other. It is indeed an explanation with 

 many obscurities and shortcomings; but all I seek to emphasize 

 is that none of them is peculiar to adaptations of Class B, i.e. 

 peculiar to adaptations of the only kind for which a Lamarckian 

 explanation is theoretically admissible. The adaptive value or 

 •"selective advantage' of having developmentally prefabricated 

 flexure lines is far from obvious; but so also is, for example, the 

 adaptive value of many of the antigenic variants that deter- 

 mine blood-group polymorphism and the incompatibilities 

 revealed by grafting — differences upon which a Lamarckian 



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