HISTORY 



11 



This theory is well set forth in the " Origin of Species/' 

 published in 1859. His great work for Zoology, and the 

 world, was to convince scientific men that there had been 

 a change in the past that one type of animal had evolved 

 from a somewhat different preexisting type. His theory 

 involved four ideas: (1) More animals are produced than 

 can find a place to live and hence there is a " struggle for 

 existence;" (2) qualities tend to be transmitted unchanged 

 from parent to offspring; but (3) there is always slight varia- 

 tion which may make one animal a little better than others 

 of its own species; and (4) there may thus be a " survival 

 of the fittest" in the struggle, which constitutes the 



FIG. 9. Darwin. (From Locy, 

 Biology and Its Makers.) 



FIG. 10. Agassiz. (From Locy, 

 Biology and Its Makers.) 



' ' natural selection ' ' 

 improved after 



through which Darwin supposed animals 

 a number of generations. This theory 

 gave a wonderful impetus to all branches of scientific work 

 because it opened a vast field for investigation by clearing 

 men's minds of the idea that natural phenomena had always 

 been and always would be as they are, and were, therefore, 

 not open to experimental study. 



AGASSIZ (1807-1873), though a Swiss by birth, is of 

 particular interest to all American zoologists. He was a 

 comparative anatomist of the school of Cuvier who came 



