166 THE SURVIVAL OF THE UNLIKE. [vi. 



that all modifications are brought about through a union 

 of the sexes. Amongst the leading philosophers who 

 hold to the direct permanent transforming effect of en- 

 vironment are Lamarck and Darwin, but these writers 

 differ as to the exact method by which this environment 

 operates upon the animal or plant. Lamarck supposes 

 that the environment or circumstances in which the 

 organism lives, — as climates, food -supply, struggle for 

 existence, care exercised by man, and the like, — cause 

 the organism to acquire new habits or functions to adapt 

 itself to these circumstances. The organism needs to 

 use one part more and another part less in the constant 

 changes in the physical conditions in which it lives, and 

 the effects of this change or modification of function 

 become hereditary. It is evident that this adaptation of 

 the organism to the environment is largely an active one 

 on the part of the organism, and that the Lamarckian 

 theory is better adapted to an application to animals 

 than to plants. 



Darwin, on the other hand, supposed that the en- 

 vironments or "changed conditions of life" are them- 

 selves the causes of variations or modifications in the 

 organism, and that those forms which are best adapted 

 to these environments tend to live and to perpetuate 

 their kind, and those which are least adapted to the 

 environments tend to disappear. This is the well-known 

 hypothesis of natural selection or survival of the fittest. 

 It is evident that this survival of the fittest is largely a 

 passive one upon the part of the organism, and that the 

 Darwinian theory is better adapted to an application to 

 plants than to animals. 



It will be seen from the above outline that both 

 Lamarckism and Darwinism teach that those characters 



