30 STRUGGLE AMONGST ANIMALS 



common field or outdoor rat, for which its hardy 

 nature is better suited, and in such situations it is 

 replacing the black rat. But so far from the black 

 rat becoming extinct, it is increasing in numbers in 

 many places, especially in ports such as London, and 

 is still common in suitable localities all over Europe. 

 In this story of the rats, which has been very carefully 

 investigated, there is no trace of a process comparable 

 with the German theory of war as an instance of the 

 struggle for existence. 



No doubt, and I understand from Sir James 

 Crichton Browne that the experiment has actually 

 been made, if a number of black and brown rats were 

 shut up together in a cage, the brown rats, as the 

 larger and heavier animals, might kill the others, 

 but such a process has played little part in nature. 

 Each species has its different aptitudes, capacities 

 and preferences, and each insinuates itself into the 

 most suitable environment. Possibly the extension 

 of sewers and drains in this country has been a major 

 cause of the greater success of the brown rat. 



A third example, also referred to quite briefly by 

 Darwin in his chapter on the Struggle for Life, that 

 of the cockroaches, has passed into general literature 

 in a misleading fashion. These active, repulsive and 

 voracious insects are omnivorous feeders, devouring 

 almost any animal or vegetable substance. There is 

 no kind of human food from which they will refrain, 

 whether it be raw or cooked, and they will eat paper, 

 the paste from labels, the leather covers or bindings 

 of books, and all kitchen refuse. They devour the 

 bodies of other dead cockroaches, although I cannot 

 ascertain that they will actually kill each other ; 



