EARLIER THEORIES CONNECTED WITH EVOL UTIOS. 45 



Others supposed that new species might have 

 been produced by the intercrossing of old ones; 

 but this cause is now known to be physiologi- 

 cally almost impossible in a state of nature, 

 though it appears to have played a part in 

 the formation of the breeds of some of our 

 domestic animals. 



Another view, advocated by Buffon, who 

 thought that the ass was simply a degraded 

 variety of the horse, was, that new species may 

 have arisen from degradation of character. 

 His illustration was peculiarly unfortunate ; for 

 the wild ass is a creature as well adapted to its 

 surroundings as the wild horse ; and although 

 congeneric, cannot be regarded in any sense as a 

 degraded creature. Although degradation may 

 possibly have occured in individual species, and 

 others appear to retrograde in their metamor- 

 phoses, yet the great majority of existing species 

 are certainly not inferior to their predeces- 

 sors ; and the continued differentiation between 

 existing organisms seems to be sufficient to 

 insure steady progress on the whole. Apparent 

 retrogression, as exhibited in the extinction 

 of species and individuals, will afterwards be 

 shown to be the necessary ally of real progress. 



