NATURAL SELECTION 67 



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, assur- 

 edly, 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 yel- 

 low 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 un- 

 important, 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 domestication, ap- 

 pear at any particular period of life, tend to reappear in the off- 

 spring at the same period; for instance, in the shape, size, and 

 flavor of the seeds of the many varieties of our culinary and agri- 

 cultural 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 in a state of nature natural selection will be en- 

 abled to act on and modify organic beings at any age, by the ac- 

 cumulation of variations profitable at that age, and by their in- 

 heritance 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 selec- 

 tion, than in the cotton-planter increasing and improving by selec- 

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

 may modify and adapt the larva of an insect to a score of con- 

 tingencies, wholly different from those which concern the mature 

 insect; and these modifications may affect, through correlation, 

 the structure of the adult. So, conversely, modifications in the 

 adult may affect the structure of the larva; but in all cases natu- 

 ral selection will insure that they shall not be injurious: for if they 

 were so, the species would become extinct. 



Natural selection will modify the structure of the young in re- 

 lation 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 whole community; if the community profits by 

 the selected change. What natural selection cannot do, is to mod- 

 ify the structure of one species, without giving it any advantage, 



