ii STABILITY OF SPECIES 103 



affinity and of definite divergence. 

 Linnaeus applied this principle to the 

 living world as it exists now, and his 

 famous Binomial system, which survives 

 to the present day, assumes, as a fact, 

 that in that world genera and species are 

 practically stable. Cuvier, on the other 

 hand, was largely concerned with the 

 extinct forms of life, and his classification 

 of them, and his identification of their 

 relations with living forms, would have 

 been impossible if the peculiarities of the 

 structure in all living things had not 

 maintained through unknown ages the 

 same persistent character. He therefore 

 declared, with truth, that the very 

 possibility of establishing a science of 

 natural history absolutely depends on 

 the stability of species. 



If, then, we give up the idea that 

 species have been permanently immut- 

 able, we must beware of rushing off to 



