300 The Study of Animal Life part iv 



There are evidently three direct ways in which organic 

 changes may be produced : ( i ) From the nature of the 

 organism itself; i.e. from constitutional or germinal peculiar- 

 ities which are ultimately traceable to influences from 

 without ; (2) from changes in its functions or activity, in 

 other words, from use and disuse ; or (3) from the direct 

 influence of the external conditions of life — food, temperature, 

 moisture, etc. 



Thus some naturalists follow Buffbn in emphasising the 

 moulding influence of the environment, or agree with 

 Lamarck in maintaining that change of function produces 

 change of structure. But at present the tide is against 

 these opinions, because of the widespread scepticism as to 

 the transmissibility of characters thus acquired. 



Those who share this scepticism refer the origin of 

 variations to the nature of the organism, to the mingling 

 of the two different cells from which the individual life 

 begins, to the instability involved in the complexity of the 

 protoplasm, to the oscillating balance between vegetative 

 and reproductive processes, and so on. 



One prevalent opinion regards variations as arbitrary 

 sports in " a chapter of accidents," but according to the 

 views of a minority variations are for the most part definite, 

 occurring in a few directions, fixed by the constitutional 

 bias of the organism. The minority are " Topsian " evolu- 

 tionists who believe that the modification of species has 

 taken place by cumulative growth, influenced by function 

 and environment, and pruned by natural selection. To the 

 majority the theory that new species result from the action 

 of natural selection on numerous, spontaneous, indefinite 

 variations, is the " quintessence of Darwinism " and of truth. 



Until we know much more about the primary factors 

 which directly cause variations it will not be possible to 

 decide in regard to the precise scope of natural selection 

 and the other secondary factors which foster or accumulate, 

 thin or prune, which in short establish a new organic 

 equilibrium. The argument has been too much in regard 

 to possibilities, too little in regard to observed facts of 

 variation. 



