570 APPLIED BIOLOGY 



500. Natural selection, meaning selection by nature, is a 

 term applied to the preservation of the favored or best 

 adapted individuals in the struggle for existence ( 499). 

 For example, a grasshopper with legs adapted for jumping 

 farther than can other individuals of the same kind has a 

 better chance of surviving by escaping enemies. Hence, it 

 is said that nature selects such best fitted individuals. 

 These will have a chance to propagate ; and, according to the 

 laws of heredity ( 501), will tend to transmit their own pecul- 

 iar structure to descendants. 



Darwin's " Origin of Species," was designed to show how 

 natural selection working for tens of thousands of years and 

 generations might have led to great changes in organisms. 

 For example, the best jumping grasshoppers surviving in 

 each generation would lead, in the course of long series of 

 years, to the perfectly adapted legs of existing grasshoppers. 

 Thus a new kind or species might have arisen. 



Only one organ (leg) has been considered above, but it 

 should be noted that any important organ might affect the 

 question of survival in the same way. 



It also should be noted that only useful things could be 

 selected by nature. For example, a tumbler-pigeon, which 

 occasionally turns somersaults while flying, would not have 

 been preserved by natural selection. In fact, the habit is 

 not only useless, but in nature probably would lead to de- 

 struction by birds of prey which could easily capture a pigeon 

 during the delay in tumbling. But under human care and 

 artificial selection, these peculiar pigeons have been pre- 

 served as curiosities or freaks, and allowed to multiply. 



Numerous peculiarities of structure and color in many 

 domesticated animals and plants have been preserved by 

 artificial selection; but not being useful would not have 

 developed under natural selection. 



Seedless plants and double flowers tending to become 

 seedless could not have developed except under artificial 



