72 CHARLES DARWIN. 



many varieties to survive the parent species and 

 to give rise to successive variations departing further 

 and further from the original type." The same 

 principle explains the tendency of domestic animals 

 to return to the parent form. 



" The life of wild animals is a struggle for 

 existence." To procure food and escape enemies 

 are the primary conditions of existence, and deter- 

 mine abundance and rarity, frequently seen in 

 closely allied species. 



" Large animals cannot be so abundant as small 

 ones ; the carnivora must be less numerous than the 

 herbivora," eagles and lions than pigeons and ante- 

 lopes. Fecundity has little or nothing to do with 

 this. The least prolific animals would increase 

 rapidly if unchecked. But wild animals do not 

 increase beyond their average ; hence there must 

 be an immense amount of destruction. The abun- 

 dance of species in individuals bears no relation 

 whatever to their fertility. Thus the excessively 

 abundant passenger pigeon of the United States 

 lays only one or two eggs. Its abundance is ex- 

 plained by the widespread supply of food rendered 

 available by its powers of flight. The food-supply 

 "is almost the sole condition requisite for ensuring 

 the rapid increase of a given species." This explains 

 why the sparrow is more abundant than the red- 

 breast, why aquatic species of birds are specially 

 numerous in individuals, why the wild cat is rarer 

 than the rabbit. " So long as a country remains 



