FACTORS OF LAMARCK'S THEORY 99 



The first factor, therefore, is made up by changes that 

 are wrought in this way. The second factor is Heredity, 

 by which it is supposed that these changes are trans- 

 mitted ; and it is certainly true that if such transmission 

 is possible, some amount of evolution must result. You 

 will all be prepared to admit that if these two factors 

 represent facts, their co-operation must produce some 

 amount of evolution. 



It is important to remember, however, that both factors 

 are not undisputed, as are the three factors of Dar- 

 winian Evolution. Although we all admit the existence 

 of acquired characters as the effect of external causes 

 upon the individual during its life, yet biologists are by 

 no means agreed that these effects are hereditary, and, 

 if not, the acquired character ends with the individual 

 in which it arose, and, not being handed on, can never 

 become a character of the species. It is impossible for 

 those who hold the Lamarckian or Spencerian view to 

 escape from this. If it is true that such characters are 

 transmitted, then the foundation of the theory is secure ; 

 but the transmission of acquired characters is by no 

 means proved. Herbert Spencer has preferred to occupy 

 himself in building a magnificent edifice upon this founda- 

 tion, rather than employ his acute intellect in testing its 

 firmness and security in every possible way. 



So far as observation goes, all those characters 

 which are believed by many to owe their origin to 

 the Lamarckian principle are present, actually or poten- 

 tially, in the individual before the beginning of its active 

 life, before the operation of those causes which were 

 believed originally to account for the characters. Accord- 

 ing to the Lamarckian Theory such characters have 

 already become hereditary ; and therefore it is of essential 

 importance to the Lamarckian to prove that acquired 

 modifications can be and are transmitted. Only in this 

 way can he give good grounds for the opinion that such 

 characters, when they occur ready-made in the individual, 

 are to be explained by the action of external causes 

 during the lives of ancestors. 



These are the two main theories of evolution. There 



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