CHAPTER XXXVII 

 THE SPECIES 



THE word species is in current use and its meaning seems 

 clear enough not to need definition. We know the species 

 man, horse, trout, viper, pear-tree ; and, so long as there 

 is question only of such forms remote from each other, there 

 is no difficulty. No one has any doubt in presence of such 

 types. The difficulty begins with forms having great affi- 

 nities with each other, such as the horse and ass, hare and 

 rabbit, bulldog and poodle. Among such neighbouring 

 forms we hesitate and essay an estimate of the differences 

 which separate the two types, so as to come to a reasonable 

 conclusion. In some cases the answer may be disconcert- 

 ing to people not prepared for it. For example, the horse 

 and ass are said to be of different species, while Dane and 

 King Charles are ranked in the same species dog ; and 

 yet it is plain that the descriptive differences between the 

 two dogs are far more considerable than those which we 

 detect between the horse and the ass. 



At bottom, under all this question about species, there 

 lies an error of method. 



For a very long time men had an idea that species were 

 entities created separately and existing each on its own 

 hook. In other words, it was believed that there was some 

 absolute definition of species. The belief persisted even 

 after the discovery of the transformation of species and 



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