826 president's address. 



of a modus oijerandi in the way of natural causation as is for us 

 supplied by the selection theory. 



That theory is indeed the answer to Kant's demand for a 

 " mechanism of Nature " which should " give us an insight into 

 the generation " of organic forms, and should confirm his supposi- 

 tion that these " have an actual blood-relationship, due to 

 derivation from a common parent." That natuivil selection has 

 justified its claim to be considered as just such a "mechanism of 

 Nature " — as a determining factor in evolution — few if any will 

 now denv. Whether or not, on the other hand, it is an all- 

 suflicient explanation of the appearance of new structural features, 

 and thus of new organic forms, or whether the Lamarckian factor 

 of use-inheritance also plays the part of an integral factor in the 

 process, is even now the subject of most energetic controversy. 

 Into the details of that controversy I do not propose to enter. I 

 would only point out that if the latter factor be admitted to 

 equal rights with the former, the problem of the mode of natural 

 operation, or the mechanism, whereby the effects of use are 

 registered and expressed in definite and transmissible structural 

 alteration, still remains unsolved. But after all this question is 

 not quite a fundamental one. Whether on strictly selectionist 

 principles alone, or with the admission also of use-inheritance, the 

 factor of variation is implied and assumed. Whether, as the 

 selectionist holds, variation is indefinite, and occurs indifferently 

 in all possible directions, or whether, with the Lamarckian, we 

 admit that variation is frequently in a definite and determinate 

 direction, there is yet an element in the chain of natural causation 

 which is fully explained on neither supposition. 



It is true that emphasis may be laid, as by Mr. Spencer, and 

 as earlier by St. Hilaire, on the determining effect of environment. 

 But it is next to impossible to prove — and certainly it has not 

 been proved — that simply of itself environment can do anything 

 at all. We can never fully eliminate or distinguish what is due 

 to the reaction of the organism to the environing conditions. 

 Organism is never passive. The distinguishing feature of life 

 consists in activity in the way of adaptation, whether we view it 



