Characters, Hereditary and Acquired. 153 



important results. And, even so, it is to be re- 

 membered that the importance of such results is 

 not to be estimated by the magnitude of modification. 

 Far more is it to be estimated by the character 

 of modification as adaptive. For if functionally 

 produced changes, and changes produced in adaptive 

 response to the environment, are ever transmitted 

 in a cumulative manner, a time must sooner or 

 later arrive when they will reach a selective value 

 in the struggle for existence when, of course, they 

 will be rapidly augmented by natural selection. 

 Thus, if in any degree operative at all, the great 

 function of these principles must be that of supplying 

 to natural selection those incipient stages of adaptive 

 modifications in all cases where, but for their 

 agency, there would have been nothing of the kind 

 to select. Themselves in no way dependent on 

 adaptive modifications having already attained a 

 selective value, these Lamarckian principles are 

 (under the Darwinian theory) direct causes of deter- 

 minate variation in adaptive lines ; and variation 

 in those lines being cumulative, the result is that 

 natural selection is in large part presented with the 

 raw material of its manufacture special material of 

 the particular kinds required, as distinguished from 

 promiscuous material of all kinds. And the more 

 complex the manufacture the more important will 

 be the work of this subordinate factory. We can 

 well imagine how the shell of a nut, for instance, 

 or even the protective colouring of an insect, may 

 have been gradually built up by natural selection 

 alone. But just in proportion as structures or organs 

 are not merely thus of passive use (where, of course, 



