NATURAL SELECTION. 79 



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 tlie variations are 

 accumulated through natural selection, other modifica- 

 tions, often of the most unexpected nature, will ensue. 



As we see that those variations which, under domesti- 

 cation, 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 dis- 

 seminated 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 selection 

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

 contingencies, wholly different from those which concern 

 the mature insect; and these modifications may eft'ect, 

 through correlation, the structure of the adult. So, con- 

 versely, modifications in the adult may affect the structure 

 of the larva; but in all cases natural 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 

 m 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 whole community; 

 if the community profits by the selected change. V, hat 



