28 UilGANlC EVOLUTION — PHYSICAL 



more rapid than would at first sight appear, for it is 

 probable that but a few seminal generations intervene 

 between the most divergent cultivated plants and their 

 wild progenitors. But now suppose we chose any one 

 of these highly divergent varieties, and without using any 

 selection, bred from seed alone, what would happen ? 

 There is ample evidence leading us to believe that in 

 the vast majority of instances the variety would 

 swiftly (^. e. in a very few generations) revert to some- 

 thing very like the wild stock from which they 

 originally descended ; — but not to the wild stock 

 precisely, for no doubt while the cultivated species was 

 undergoing evolution in one direction, it was under the 

 changed conditions undergoing retrogression in other 

 particulars, and in these the reverted variety would 

 differ from the original stock. 



The truth therefore appears to be, that while there is 

 a limit within " assigned " time to evolution, there is 

 practically none to retrogression. 



The above considerations may afford an explanation 

 of another set of facts, viz. that cultivated plants and 

 domesticated animals are much more variable than the 

 wild varieties of the same species. In a state of nature 

 plants and animals exist under conditions which, 

 normally, are uniforin during long ages ; owing to 

 which, and to the circumstance that in a state of nature 

 many traits are essential to survival, evolution is slow, 

 and therefore the traits of wild animals and plants 

 acquire a certain fixity, because if any recent ancestor 

 be reverted to in any particular, the change is not 

 great; moreover, any retrogression must generally 

 cause elimination ; therefore since evolution is slow, 

 since any reversion can seldom bo great, and since 

 reversion tends to cause elimination, there can seldom 

 be any great or observable change of form. With 

 cultivated plants and domesticated animals fewer 



