152 EVOLUTION 



varieties, which suggests that they origi- 

 nated as such. 



Struggle for Existence. — The term 

 "struggle for existence" is used in a large 

 and metaphorical sense, including depend- 

 ence of one being upon another, and em- 

 bracing (which is more important) not only 

 the life of the individual, but success in 

 leaving progeny. From the high (geo- 

 metrical) rate of increase of all organic be- 

 ings (even the slow breeders requiring only 

 a few more years to people a whole district) 

 struggle inevitably follows, either one in- 

 dividual with another of the same species, 

 or with the individuals of a distinct species, 

 or with the physical conditions of life. It is 

 the doctrine of Malthus applied with mani- 

 fold force to the entire animal and vegetable 

 kingdoms, for in this case there can be no 

 artificial increase of food and no prudential 

 restraints from marriage. 



The checks to increase are very obscure. 

 Eggs or young animals generally suffer most, 

 and plants, mostly as seedlings, both from 

 germinating on ground already occupied and 

 from animals. The amount of food, of 

 course, gives the extreme limit of numbers; 

 very frequently, however, the check is 

 given by the attacks of enemies, as on game 

 by "vermin." Changes of climate play an 



