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 



