ADDKESS. 



21 



<yf this initial tendency to vary, as well as those of its limits and pre- 

 vailing direction, and the circumstances which favour its occasional burst- 

 ing through the constraining principle of heredity offer an endless field 

 for speculation. Thongh several theories of variation have been sug- 

 gested, I think that no one would venture to say we have passed beyond 

 the threshold of knowledge of the subject at present. 



Taking for granted, however, as we all do, that this tendency to 

 individual variation exists, then comes the question, What are the agents 

 by which, when it has asserted itself, it is controlled or directed in 

 fluch a manner as to produce the permanent or apparently permanent 

 modifications of organic structures which we see around us ? Is ' survival 

 of the fittest ' or preservation by natural selection of those variations best 

 adapted for their surrounding conditions (the essentially Darwinian or 

 still more essentially Wallacian doctrine) the sole or even the chief of 

 these agents ? Can isolation, or the revived Lamarckian view of the direct 

 action of the environment, or the effects of use or disuse accumulating 

 through generations, either singly or combined, account for all ? or is it 

 necessary to invoke the aid of any of the numerous subsidiary methods 

 of selection which have been suggested as factors in bringing about the 

 great result ? 



Anyone who has closely followed these discussions, especially those 

 bearing most directly upon what is generally regarded as the most 

 important factor of evolution— natural selection, or ' survival of the 

 fittest '—cannot fail to have noticed the appeal constantly made to the 

 advantage, the utility, or otherwise of special organs or modifications of 

 organs or structures to their possessors. Those who have convinced 

 themselves of the universal application of the doctrine of natural selection 

 hold that every particular structure or modification of structure must be 

 of utility to the animal or plant in which it occurs, or to some ancestor 

 of that animal or plant, otherwise it could not have come into existence ; 

 the only reservation being for cases which are explained by the principle 

 which Darwin called ' correlation of growth.' Thus the extreme natural 

 selectionists and the old-fashioned school of teleologists are so far in 

 agreement. 



On the other hand, it is held by some that numerous structures and 

 modifications of structures are met with in nature which are manifestly 

 useless; it is even confidently stated that there are many which are 

 positively injurious to their possessor, and therefore could not possibly 

 have resulted from the action of natural selection of favourable variations. 

 Organs or modifications when in an incipient condition are especially 

 quoted as bearing upon this difficulty. But here, it seems to me, we are 

 continually appealing to a criterion by which to test our theories of which 

 we know far too little, and this (though often relied upon as the strongest) 

 is, in reality, the weakest point of the whole discussion. 



Of the variations of the form and structure of organic bodies we are 



