CuAP. HI. GEOMETRICAL KATIO OF INCREASE. 71 



forget, tliat the birds which arc idly singing round us mostly 

 live on insects or seeds, and are thus constantly destroying 

 life ; or we forget how largely these songsters, or their eggs, 

 or their nestlings, are destroyed by birds and beasts of prey ; 

 we do not always bear in mind, that, though food may be now 

 superabundant, it is not so at all seasons of each recurring 

 year. 



Tlie 2h'm, Stu-uggle for Existence^ used in a Large Sense. 



I should premise that I use this term in a large and meta- 

 phorical sense, including dependence of one being on another, 

 and including (which is more important) not only the life of 

 the indi\-idual, but success in lea\'ing progeny. Two canine 

 animals, in a time of dearth, may be truly said to struggle with 

 each -other which shall get food and live. But a plant on the 

 edge of a desert is said to struggle for life against the drought, 

 though more properly it should be said to be dependent on the 

 moisture. A plant which annually produces a thousand seeds, 

 of which on an average only one comes to maturity, may be 

 more truly said to struggle with the plants of the same and 

 other kinds which already clothe the ground. The mistletoe 

 is dependent on the apple and a few other trees, but can only 

 in a far-fetched sense be said to struggle with these trees, for, 

 if too many of these parasites grow on the same tree, it will 

 languish and die. But several seedling mistletoes, growing 

 close together on the same branch, may more truly be said to 

 struggle with each other. As the mistletoe is disseminated by 

 birds, its existence depends on birds ; and it may metaphori- 

 cally be said to struggle with other fruit-bearing plants, in 

 order to tempt birds to devour and thus disseminate its seeds 

 rather than those of other plants. In these several senses, 

 which pass into each other, I use for convenience' sake the 

 general term of struggle for existence. 



Geometrical Ratio of Increase. 



A struggle for existence inevitably follows from the high 

 rate at which all organic beings tend to increase. Every being 

 which during its natural lifetime produces several eggs or 

 seeds, must suffer destruction during some period of its life, 

 and during some season or occasional year, otherwise, on the 

 principle of geometrical increase, its numbers would quickly 



