Recent Developments in Heredity and Evolution ii 



generation, which in turn would add to it, until a number 

 of generations would succeed in developing the exaggerated 

 neck of the giraffe. 



This illustration makes clear the factors relied upon by 

 Lamarck, namely, the effect of use demanded by changed 

 conditions, and the transmission of the changes from parent 

 to offspring. His own name, "appetency," sought to ex- 

 press the idea of striving to satisfy a desire; but, as might 

 have been expected, it was not understood by most of the 

 people of his day, and lent itself admirably to all sorts of 

 caricature. 



The changes in structure brought about during the life 

 of an individual are spoken of as "acquired characters," 

 and Lamarck's explanation of the evolutionary process 

 would be impossible if acquired characters are not trans- 

 mitted from parent to oft'spring. The present consensus of 

 opinion seems to be that such acquired characters as 

 Lamarck had in mind are not transmissible; but the whole 

 subject of the transmission of acquired characters is more 

 a matter of definition than anything else. 



3. Natural selection. — It was the explanation offered by 

 Charles Darwin, however, that proved to be the most 

 epoch-making theory in the history of biological science. 

 He called it "natural selection," and it has been a domi- 

 nating conception for fifty years. With the Darwin 

 centennial celebrations only two years old, and with the 

 flood of literature that accompanied and followed them, 

 no one interested in the subject of evolution can be ignorant 

 of the meaning of natural selection, or of the revolution in 

 thought and method brought about by its presentation in 

 Darwin's Origin of Species. While Lamarck's conception 

 was based upon extensive observation, and therefore was 



