CHAPTER I. 



ARE SPECIES MUTABLE? 



THE subject around which the question of evolu- 

 tion is centred is the immutability of species. Are 

 species so stable that they always produce offspring 

 like themselves, or can they change so as to give 

 rise either slowly or rapidly to new ones? If evolu- 

 tion is a fact, the latter must, of course, be true. 

 Most naturalists claim that the evidence accumu- 

 lated is sufficient to establish beyond a reasonable 

 doubt the fact that species are mutable. They look 

 upon those living to-day as descended from past 

 species, from which they differ ; and as continually 

 changing, so that they will, in turn, give rise to new 

 species in the future. Indeed, the term species is 

 considered as having no real significance, but as 

 simply a convenient method of classing similar or- 

 ganisms together. If this be admitted, the whole 

 problem of organic evolution is in reality conceded ; 

 for when once it is recognized that species are 

 derived from each other by descent, the method of 

 this derivation, and the number of originally created 

 forms, are simply matters of detail. But this posi- 

 tion is not everywhere conceded, for it is still claimed 

 by a few that the evidence is not sufficient to war- 



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