116 ANIMAL LIFE 
est breeder of all known animals. It begins breeding when 
thirty years old and goes on breeding until ninety years 
old, bringing forth six young in the interval, and surviving 
till a hundred years old. If this be so, after about eight 
hundred years there would be 19,000,000 elephants alive, 
descended from the first pair.” A few years more of the 
unchecked multiplication of the elephant and every foot of 
land on the earth would be covered by them. 
Yet the number of elephants does not increase. In gen- 
eral, the numbers of every species of animal in the state of 
Nature remain about stationary. Under the influence of 
man most of them slowly diminish. There are about as 
many squirrels in the forest one year as another, about as 
many butterflies in the field, about as many frogs in the 
pond. Wolves, bears, deer, wild ducks, singing birds, fishes, 
tend to grow fewer and fewer in inhabited regions, because 
the losses from the hand of man are added to the losses in 
the state of Nature. 
It has been shown that at the normal rate in increase of 
English sparrows, if none were to die save of old age, it 
would take but twenty years to give one sparrow to every 
square inch in the State of Indiana. Such an increase is 
actually impossible, for more than a hundred other species 
of similar birds are disputing the same territory with the 
power of increase at a similar rate. There can not be food 
and space for all. With such conditions a struggle is set 
up between sparrow and sparrow, between sparrow and 
other birds, and between sparrow and the conditions of life. 
Such a conflict is known as the struggle for existence. 
69. The struggle for existence.—The struggle for exist- 
ence is threefold: (a) among individuals of one species, 
as sparrow and sparrow; (6) between individuals of differ- 
ent species, as sparrow with bluebird or robin ; and (c) with 
the conditions of life, as the effort of the sparrow to keep 
warm in winter and to find water in summer. All three 
forms of this struggle are constantly operative and with 
