VARIATION. 77 



maintains a race of non-milkers. I am inclined 

 to believe that Jersey calves allowed all their 

 mother's milk till eight months old would pro- 

 duce in a few generations cattle inclined to 

 vary to a higher type of beef cattle; excessive 

 nutriment being the great cause of variation, 

 as floriculturists and horticulturists have won- 

 derfully shown. 



But I shall not multiply instances of corre- 

 lated variation, nor shall I go more deeply into 

 this great, complex, and inadequately under- 

 stood subject. We have seen that under 

 changed conditions of life all animals tend to 

 vary; that such variations as are thus produced 

 may be made permanent by selection; that such 

 a variation is prepotent over a normal charac- 

 teristic, and is generally complex rather than 

 single, affecting more than one organ, and that 

 certain organs are so intimately related that 

 any modification of one is accompanied or fol- 

 lowed by a modification of the other. 



