NATURE, HISTORY, AND ETHICS 4OI 



animals of earlier ages as the ancestors of living 

 animals, and to determine the historical lines of 

 development. The law which says that animals 

 resemble each other in proportion to their blood- 

 relationship gives us the right to take their structure 

 as evidence of their ancestral history. And there are 

 still other laws. 



However, these laws only justify historical investi- 

 gation ; they do not supply the place of it. They 

 apply wherever there are organisms, and therefore they 

 cannot discuss the particular process of the modifica- 

 tion of a species, A law that has only held good in 

 one particular case is an impossibility, because every 

 law is formulated by regarding the common element in 

 a number of phenomena. Hence the laws of science 

 can never bridge over the interval between two 

 distinct stages of organic evolution ; indeed, one 

 might be acquainted with all the laws that apply 

 to organic evolution yet have no idea of the real 

 course of this development. 



The laws can never tell us, for instance, how birds 

 were developed from reptiles. Again, if there were 

 a law which said that in the rise of a nation there 

 were always great men who led the people, we should 

 not understand from this law alone why Luther in 

 particular appeared at the Reformation, or Bismarck 

 at the rise of modern Germany, and why these 

 special individuals led the people. 



It is in the very nature of the evidence for animal 

 evolution to be grounded on greater or less probabilities. 



2 c 



