CREATION BY EVOLUTION 



Darwinian naturalists believed. A species is an expression 

 of opinion, not of fact. 



Persistent efforts were made to delimit species by the 

 sterility of hybrids. The fact that the mule is sterile was 

 set up as proof that the horse and the donkey are different 

 species. But the rule that hybrids are sterile is subject to 

 many exceptions; thus the rabbit and the hare have a fertile 

 hybrid known as he pus danvinii, and so have the common 

 and the Chinese goose, which are classified as unquestion- 

 ably distinct species. Conversely, crosses between many 

 domesticated varieties of plants are sterile. 



The fact that a species is an arbitrary and not a well- 

 defined natural unit is further shown by variations of organ- 

 isms from the standard types. Herbert Spencer, in 1852,^ 

 years before the publication of Darwin's Origin of Species, 

 claimed that it had already been proved that "any existing 

 species — animal or vegetable — when placed under conditions 

 different from its previous ones, ijjimediately begins to 

 undergo certain changes of structure fitting it for the new 

 conditions. They [the supporters of the theory of natural 

 development] can show that in cultivated plants, in domes- 

 ticated animals, and in the several races of men, such altera- 

 tions have taken place. They can show that the degrees of 

 difference so produced are often, as in dogs, greater than 

 those on which distinctions of species are in other cases 

 founded. They can show that it is a matter of dispute 

 whether some of these modified forms are varieties or sepa- 

 rate species." 



Some variations are obviously due to the influence of 

 environment and of mode of living — of daily work. Varia- 

 tions that are successive and cumulative in time have been 

 called mutations (Waagen, 1868) , though that term has been 



^ Reprinted in Essays, Vol. 1, pp. 379-80, 1868. 



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