58 THE SURVIVAL OF THE UNLIKE. [ll. 



conditions of life ; ' ' and he was a firm believer in the 

 hereditability of acquired characters. It is around these 

 two great hypotheses — the functional or Lamarckian on 

 the one hand, and the selective or Darwinian upon the 

 othei' — in various forms and modifications, that the dis- 

 cussions of the philosophy of organic nature are at 

 present revolving. 



Before leaving the subject of Darwinism, I wish to 

 touch upon Darwin's view of the cause of variation and 

 his belief in the transmission of acquired characters. We 

 shall presently see that the rehabilitation of the theo- 

 ries of Lamarck, under the name of Neo-Laraarckism, is 

 undertaken, very largely, for the purpose of assigning 

 the origin of variations to external causes, or to the en- 

 vironment, in opposition to those who consider the source 

 of variation to be essentially innate, or at least internal. 

 But Darwin also believed that variation is induced by 

 the environment, and the chief factor in this environment, 

 so far as its reaction upon the organism is concerned, is 

 probablj' excess of food supply, although climate and 

 other impinging circumstances are potent causes of 

 modification. He marshaled arguments to support "the 

 view that variations of all kinds and degrees are directly 

 or indirectly caused by the conditions of life to which 

 each being, and more especially its ancestors, have been 

 exposed," and that "each separate variation has its own 

 proper exciting cause." I do not understand how it has 

 come about that various writers declare that Darwin did 

 not believe explicitly in the external cause of variation, 

 and that they fed obliged to go back to Lamarck in or- 

 der to find a hypothesis for the occasion. It is true that 

 Darwin believed that the nature or direction or particu- 

 lar kind of variation in a given case is determined very 



