4O INHERITANCE, VARIATION AND SELECTION. 



applies less to the organs than it does to the functions of the organs, 

 and that when it applies to the organs themselves, it does so only 

 through their functions. The reasons for this and the causes lead- 

 ing to earlier or later appearance of inherited characters will be 

 explained in a later chapter. 



SELECTION. 



When a litter of pigs is born, according to the laws of heredity 

 they are like their mother, and according to the laws of variation 

 we find that they differ one from another. When they have grown 

 to mature size we find that some are larger and some are smaller 

 than the mother. If we should select the largest female and from 

 her and the largest obtainable male we raise another litter, it will 

 again be found that some grow to a size larger and some to a size 

 smaller than the new mother. Again selecting the largest male and 

 female for another litter, we again find variations in size above and 

 below the size of the parents, and we will have some specimen 

 larger than any immediate ancestor. Although these variations in 

 size from generation to generation are slight, it will be evident that 

 by accumulating these slight variations it will only be a question of 

 time until a race of pigs would be produced as large as elephants. 

 If, on the other hand, instead of selecting the largest from which 

 to breed the next generation, we should continually select the small- 

 est, it would be only a question of time when we should have pigs 

 as small as mice. 



Although this is a hypothetical proposition it is not an absurd- 

 ity. That such variations occur we know, and no man has yet 

 found any point, or indication of a point, where they cease. In 

 reality our hypothetical case represents only a small fraction of 

 what the scientific world now accepts as a fact. That fact is that 



