NATURAL SELECTION 1489 



would produce little effect: we should remember 

 how essential it is in a flock of white sheep to destroy 

 a lamb with the faintest trace of black. In plants, 

 the down on the fruit and the color of the flesh are 

 considered by botanists as characters of the most 

 trifling importance: yet we hear from an excellent 

 horticulturist, Downing, that in the United States 

 smooth-skinned fruits suffer far more from a beetle, 

 a Curculio, than those with down; that purple plums 

 suffer far more from a certain disease than yellow 

 plums ; whereas another disease attacks yellow-fleshed 

 peaches far more than those with other colored flesh. 

 If, with all the aids of art, these slight differences 

 make a great difference in cultivating the several va- 

 rieties, assuredly, in a state of nature, where the trees 

 would have to struggle with other trees and with a 

 host of enemies, such differences would effectually 

 settle which variety, whether a smooth or downy, a 

 yellow or purple fleshed fruit, should succeed. 



In looking at many small points of difference be- 

 tween species, which, as far as our ignorance permits 

 us to judge, seem quite unimportant, we must not 

 forget that climate, food, etc., have no doubt pro- 

 duced some direct effect. It is also necessary to bear 

 in mind that, owing to the law of correlation, when 

 one part varies, and the variations are accumulated 

 through natural selection, other modifications, often 

 of the most unexpected nature, will ensue. 



Natural selection will modify the structure of the 

 young in relation to the parent, and of the parent in 

 relation to the young. In social animals it will adapt 

 the structure of each individual for the benefit of the 



