LIMITS OF VARIATION. 3! 



Two conclusions can at least be unhesitatingly 

 drawn : i. Variations are partly dependent upon 

 external conditions. 2. They are not wholly so de- 

 pendent. 



Limits of Variation. 



A very great amount of variation is thus proved 

 and everywhere admitted. The question for discus- 

 sion is not as to its existence but as to its limitation. 

 Is it unlimited ? Can any variation go on increasing 

 generation after generation, until new species arise 

 by a continual accumulation of variations? Evi- 

 dently if these variations are not limited, but can 

 continue indefinitely, becoming greater with suc- 

 ceeding generations, the final result would be such 

 great differences between animals as to form new 

 species. And this is the position that is held by 

 most evolutionists, though not by all. New species 

 are believed to have arisen by the accumulation of 

 variations, each slight in amount, but when added 

 together becoming sufficient to constitute the differ- 

 ences between species. Variations are thus consid- 

 ered as unlimited. It must, of course, be 'true 

 that there are certain limits set upon variation by 

 physical conditions. Our race-horses, for instance, 

 have been continually increasing their speed since 

 racing has become common. No limit to this varia- 

 tion has as yet been reached. But evidently there 

 must be a limit to this increase in speed toward 

 which horses can tend but beyond which they can- 

 not go. So in other features ; it is usually possible 

 to see a limit to variation set by physical conditions. 



