l3 THE MEANING OF EVOLUTION 



ing which he wrote several books describing them, he 

 finally published the great work on which his fame 

 depends. This was the "Philosophic Zoologique." 

 In this treatise he taught that the animal kingdom is 

 a unit and that all its members are blood relations ; 

 that the members vary wnth varying conditions ; that 

 this variation results in continued advance. In all of 

 these points Lamarck is at one with modern thought. 

 His idea of the method by which the variation comes 

 about has been accepted and rejected; modified, re- 

 accepted, and again rejected. 



Lamarck's conception of the cause of progress was 

 somewhat as follows: The desire for any action 

 on the part of an animal leads to efforts to accom- 

 plish that desire. From these efforts came gradually 

 the organ and its accompanying powers. With every 

 exercise of these powers the organ and its correspond- 

 ing function became better developed. Every gain 

 either in function or in organ was transmitted to 

 those of the next generation, who were thus enabled 

 to start where their parents left off. The general 

 environment constantly gave the stimuli that led to 

 the adaptive changes. 



American zo51ogists have been especially inclined 

 toward Lamarck's ideas. Until Weismann startled 

 the scientific w^orld with his sharp denial of the pos- 

 sibility of transmitting to offspring any growth ac- 



