4 THE THEOKY OF EVOLUTION 



parents) never establishes a more general or more 

 extended similarity than the ' specific similarity ' : 

 that is, the most perfect similarity which we in fact 

 know of. Progeny of the same parents never depart 

 so far from each other or even from their nearest 

 ' relatives ' that we rank them of different species, 

 and therefore we must create a ' race ' for all of 

 them in order to unite them generally. 1 



Upon this observation the opinion is based that 

 the specific similarity is above the expression of actual 

 relationship which specific similarity is always, so far 

 as we can observe it, transmitted unchanged as regards 

 the essential distinct characters in the process of 

 reproduction, i.e. remains constant : that would be 

 the doctrine of specific constancy. 



The greater or less similarity also with other animal 

 types was well recognized, but since it was seen how 

 they continued to exist together but separated, and 

 crossed either never or unwillingly or unfruitfully, 

 it struck no one that similarity, carried further, could, 

 and must, be based on descent. 



Already the attention of some investigators had 

 been aroused by certain petrifactions. Many of these 

 showed clearly the form of mussels, fish, leaves, etc., 

 but they often appeared quite different from the corre- 

 sponding animals, etc., with which man was familiar. 

 Sea mussels and sea fish were also found far inland or 



1 We choose this mode of expression purposely, which moreover cannot 

 be contested, in order to avoid long explanations as to the meaning of 

 ' species.' Compare Wasmann : Die Moderne Biologie und die EntwicUungs- 

 iheorie, chap. x. 



