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Theory of Varieties. 



Now the generally adopted opinion is that species are absolute in- 

 dependent creations, which daring their whole existence never vary 

 from one to another, while varieties are not independent creations, but 

 are or have been produced by ordinary generation from a parent spe- 

 cies. There does, therefore (if this definition is true), exist such an 

 absolute and essential difference in the nature of these two things that 

 we are warranted in looking for some other character to distinguish 

 them than one of mere degree, which is necessarily undefinable. If 

 there is no other character, that fact is one of the strongest arguments 

 against the independent creation of species, for why should a special 

 act of creation be required to call into existence an organism differing 

 only in degree from another which has been produced by existing 

 laws ? If an amount of permanent difference, represented by any 

 number up to 10, may be produced by the ordinary course of nature, 

 it is surely most illogical to suppose, and very hard to believe, that an 

 amount of difference represented by 11 required a special act of 

 creation to call it into existence. 



Let A and B be two species having the smallest amount of difference 

 a species can have. These you say are certainly distinct ; where a 

 smaller amount of difference exists we will call it a variety. You 

 afterwards discover a group of individuals C, which differ from A less 

 than B does, but in an opposite direction ; the amount of difference 

 between A and C is only half that between A and B : you therefore 

 say C is a variety of A. Again you discover another group D, exactly 

 intermediate between A and B. If you keep to your rule you are 

 now forced to make B a variety, or if you are positive B is a species, 

 then C and D must also become species, as well as all other perma- 

 nent varieties which differ as much as these do : yet you say some of 

 these groups are special creations, others not. Strange that such 

 widely different origins should produce such identical results. To 

 escape this difficulty there is but one way : you must consider every 

 group of individuals presenting permanent characters, however slight, 

 to constitute a species; while those only which are subject to such 

 variation as to make us believe they have descended from a parent 

 species, or that we know have so descended, are to be classed as va- 

 rieties. The two doctrines, of "permanent varieties" and of "spe- 

 cially created unvarying species," are inconsistent with each other. 



Alfred R. Wallace. 



