582 EVOLUTION, GENETICS, AND EUGENICS 



the proper color to each kind of grouse, and in keeping that color, 

 when once acquired, true and constant. Nor ought we to think thai 

 the occasional destruction of an animal of any particular color 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. We 

 have seen how the color of the 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 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 varieties, assuredly, in a state of nature, where the trees would 

 have to struggle with other trees and with a host of enemies, such dif- 

 ferences 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 between species, 

 which, as far as our ignorance permits us to judge, seem quite unim- 

 portant, 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 varia- 

 tions are accumulated through natural selection, other modifications, 

 often of the most unexpected nature, will ensue. 



As we see that those variations which, under domestication, 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 silk- worm; 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 in a state of 

 nature natural selection will be enabled to act on and modify organic 

 beings at any age, by the accumulation of variations profitable at that 

 age, and by their inheritance at a corresponding age. If it profit a 

 plant to have its seeds more and more widely disseminated by the 

 wind, I can see no greater difficulty in this being effected through 

 natural selection, than in the cotton-planter increasing and improving 

 by selection the down in the pods on his cotton-trees. Natural 



