AFFINITIES AND CLASSIFICATION 37 



may suppose that generally it will tend to extend 

 its range during geographical changes, and thus, 

 becoming isolated and exposed to new conditions, 

 will slightly alter and its structure by selection be- 

 come slightly remodified, thus we should get species 

 of a sub-genus and genus, as varieties of merino- 

 sheep, varieties of British and Indian cattle. Fresh 

 species might go on forming and others become ex- 

 tinct and all might become extinct, and then we 

 should have (an) extinct genus; a case formerly 

 mentioned, of which numerous cases occur in Palae- 

 ontology. But more often the same advantages 

 which caused the new species to spread and become 

 modified into several species would favour some of 

 the species being preserved : and if two of the 

 species, considerably different, each gave rise to 

 group of new species, you would have two genera ; 

 the same thing will go on. We may look at case in 

 other way, looking to future. According to mere 

 chance every existing species may generate another, 

 but if any species, A, in changing gets an advantage 

 and that advantage (whatever it may be, intellect, 

 &c., &c., or some particular structure or constitution) 

 is inherited 1 , A will be the progenitor of several 

 genera or even families in the hard struggle of 

 nature. A will go on beating out other forms, 

 it might come that A would people earth, we may 

 now not have one descendant on our globe of the 

 one or several original creations 2 . External con- 

 ditions air, earth, water being same 3 on globe, and 

 the communication not being perfect, organisms of 

 widely different descent might become adapted to 



1 (The exact position of the following passage is uncertain :) "just as it is 

 not likely every present breed of fancy birds and cattle will propagate, only 

 some of the best." 



2 This suggests that the author was not far from the principle of diver- 

 gence on which he afterwards laid so much stress. See Origin, Ed. i. 

 p. Ill, vi. p. 134, also Life and Letters, i. p. 84. 



3 That is to say the same conditions occurring in different parts of 

 the globe. 



