126 THE GENESIS OF SPECIES. [CHAP. IV. 



It appears then that, apart from fortuitous changes, there 

 are certain difficulties in the way of accepting extremely 

 minute modifications of any kind, although these difficulties 

 may not be insuperable. Something, at all events, is to be 

 said in favour of the opinion that sudden and appreciable 

 changes have from time to time occurred, however they 

 may have been induced. Marked races have undoubtedly 

 so arisen (some striking instances having been here 

 recorded), and it is at least conceivable that such may 

 be the mode of specific manifestation generally, the 

 possible conditions as to which will be considered in a 

 later chapter. 





