A COMMENTARY ON LAMARCKISM 



'strong"* or special form. The weak form may be so described 

 because it merely proposes the existence of a certain mode of 

 origin of inherited differences, without expressing any opinion 

 about the actual mechanism by which those diiferences have 

 come into being; but they are diiferences which, unlike so 

 many, are open to a Lamarckian interpretation of their origin. 

 The 'strong'' form goes farther and positively affirms that the 

 Lamarckian interpretation left open by the weak formulation 

 is in fact the correct one. 



2. THE 'WEAK' FORM OF LAMARCKISM 



The 'weak** form, then, may be expressed in these terms: 



Modifications acquired in each member of a succession of indi- 

 vidual lifetimes, as a result of recurrent responses to environmental 

 stimuli, may eventually make their appearance in ontogeny even 

 when the environmental stimuli are absent or are deliberately 

 withheld. . . . 



We may proceed at once to strengthen this formulation by 

 making it in one respect a little more particular: 



. . . and the age of appearance of these modifications in ontogeny 

 will eventually anticipate the age at which environmental stimuli 

 could in any case have been responsible for them 



This clause is separated from the main body of the formula- 

 tion merely to emphasize the fact that it is formally separable, 

 but we shall adopt the fuller and more particular formulation 

 for the good reason that every example we shall consider will be 

 shown to satisfy it. It must again be emphasized that the 'weak** 

 formulation neither embodies nor presupposes any hypothesis 

 about how acquired character differences become inherited 

 character differences: it merely states that they do in fact 

 become so. 



Before proceeding to the discussion of special examples, we 

 may ask: of which character differences may it plausibly be 



83 



