5G THE SURVIVAL OF THE UNLIKE. [ll. 



powers or organs and less exercise of others. This 

 greater or less use gradually strengthens or enfeebles the 

 organ concerned, and the modifications thus acquired are 

 preserved "through heredity to the new individuals 

 that are produced by them, provided the changes are 

 common to the two sexes, or to those that have produced 

 these new individuals." There are three things to be 

 considered in this hypothesis: 1. Changes in environ- 

 ment or the conditions of life react upon organisms in 

 the direction of their needs or functions. 2. Organs or 

 powers thus affected are modified to satisfy the new 

 demands. 3. The modifications acquired by the indi- 

 vidual are hereditary. This, then, is Laman^kism — 

 that the controlling factor or process in evolution is 

 functional, and that acquired characters are readily 

 transmissible. It is important that I still repeat 

 Lamarck's belief in the transmission of a character 

 obtained by any individual during its own lifetime, for 

 this is the starting point of the definition of an "acquired 

 character," concerning the hereditability of which the 

 scientific world is now rent. "All that nature has 

 caused individuals to acquire or lose through the influ- 

 ence of the circumstances to which their race has been 

 for a long time exposed," says Lamarck, "it preserves," 

 etc. And again: "Every change acquired in an organ 

 by an habitual exercise sufficient to have brought it 

 about is preserved thereafter through heredity," etc. 

 We shall presently observe how far this definition of an 

 acquired character has been maintained by recent 

 philosophers. 



Just fifty years after the publication of Lamarck's 

 theory, Darwin proposed a hypothesis which has had a 

 greater influence upon the habit of scientific thought 



