228 READINGS IN 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 that 
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 
