112 Evolution and Adaptation 
integration might serve to nourish the stronger individuals ; 
hunger coming on again, the next weakest might die; and the 
same process continuing, we might imagine that the bacteria 
were finally reduced to a single one which would then die in 
turn for lack of food. Like a starving shipload of men, re- 
duced by hunger to cannibalism, the life of some and finally of 
the last individual might be prolonged in the hope of rescue, 
but if this did not arrive, the last and perhaps the strongest 
individual would perish. But this is not what we find occur- 
ring in these lower organisms, for, as a rule, they gradually 
cease to increase when the food supply becomes lessened, and 
their activities slow down. Finally, when the food is gone, 
they pass into a resting stage, in which condition they can 
remain dormant for a long time, even for years. If they 
should again find themselves in favorable surroundings, 
they become active, and begin once more their round of 
multiplication. We cannot follow the individuals in such a 
culture of bacteria, but there is nothing to be seen that 
suggests a struggle for existence, if this idea conveys the 
impression of the destruction of certain individuals by com- 
petition with others. In fact, the results are in some respects 
exactly the reverse. Millions of individuals are present at 
the time when the food supply becomes exhausted, and they 
all pass into a protected resting stage. 
The enormous rate of increase in this case finds its coun- 
terpart in higher animals when the food supply, or the ab- 
sence of enemies, allows a species to multiply at its maximum 
rate of increase. The introduction of rabbits into Australia 
was followed by an enormous increase in a few years, and the 
introduction of the English sparrow into the United States 
has had a similar result. But in no country can such a 
process continue beyond a certain point, because, in the first 
place, the scarcity of food will begin to keep the birth-rate 
down, and in the second place, the increase in numbers may 
lead to an increase in the number of its enemies, or even 
