112 STUDIES IN ANIMAL LIFE. 



the fact of particular species having remained un- 

 altered during four thousand years does not add 

 the slightest weight to the evidence in favor of the 

 fixity of species. " What !" some may exclaim, " do 

 you pretend that four thousand years is not a period 

 long enough to prove the fixity of animal forms ?" 

 Yes ; I affirm that four thousand, or forty thousand, 

 prove no more than four. It is only by a fallacy 

 that the opposite opinion could gain acceptance. 

 You would not suppose that I had strengthened 

 my case if, instead of contenting myself with stating 

 reasons once, I repeated these same reasons during 

 forty successive pages ; you would remind me that 

 this iteration was not cumulation, and that no force 

 was given to my fortieth assertion which the first 

 wanted. Why, then, do you ask me to accept the 

 repetition of the same fact four thousand times over 

 as an increase of evidence? It is a familiar fact 

 that like produces like that dogs resemble dogs, 

 and do not resemble buffaloes ; this fact is, of course, 

 deepened in our conviction by the unvarying evi- 

 dence we see around us, and is guaranteed by the 

 philosophical axiom that like causes produce like 

 effects ; but when once such a conception is formed, 

 it can gain no fresh strength from any particular 

 instance. If we believe that crows are black, we 

 do not hold that belief more firmly when we are 

 shown that crows were black four thousand years 

 ago. In like manner, if it is an admitted fact that 

 individuals always reproduce individuals closely re- 



