74 NATURAL SELECTION. 



countless numbers ; they are known to suffer largely from 

 birds of prey ; and hawks are guided by eyesight to their 

 prey — so much so that on parts of the Continent persons 

 are warned not to keep white pigeons, as being the most 

 liable to destruction. Hence natural selection might be 

 effective in giving the proper color to each kind of grouse, 

 and in keeping that color, when once acquired, true and 

 constant. Nor ought we to think that the occasional 

 destruction of an animal of any particular color would pro- 

 duce 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. We have seen how the color of hogs, which 

 feed on the "paint-root" in Virginia, determines whether 

 they shall live or die. In plants, the down on the fruit and 

 the color of the flesh are considered by botanists as charac- 

 ters of the most trifling importance ; yet we hear from an 

 excellent horticulturist, Downing, that in the United States 

 the 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 varieties, 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 a 

 purple fleshed fruit, should succeed. 



In looking at many small points of difference between 

 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 produced 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. 



As we see that those variations which, under domestica- 

 tion, appear at any particular period of life, tend to reappear 

 in the offspring at the same period ; for instance, in the 

 shape, size, and flavor of the seeds of the many varieties of 

 our culinary and agricultural plants ; in the caterpillar and 

 cocoon stages of the varieties of the silkworm ; in the eggs 

 of poultry, and in the color of the down of their chickens ; 

 in the horns of our sheep and cattle when nearly adult; so 



