36 GENERAL PRLXCIPLES OE ZOOLOGY 



be hlottLxi out Ijy acciilcnUil causes: yel on (he whole those individuals 

 which arc liest protected «ill Kest withstand ad\-crse co)ulilions. SHght 

 superiority in structure will Ijc of importance in this struggle for existence, 

 and the possessors of this will gain an advantage over their companions 

 of the same species, just as in domestication each character which is 

 useful to man is of advantage to the possessor. Among the numerous 

 varieties that an[x\ir llie latest will survi\-c, and in the course of many 

 generations the fortunate variations will increase by summation, while 

 destruction overtakes the untit. Thus will arise new forms, which owe 

 their existence to 'natural selection in the struggle for existence.' 



The 'Struggle for Existence.' — The expression 'struggle for exis- 

 tence' is figurative, for only rarely does a conscious struggle decide the 

 question of an animal's existence; for example, in the case of the beasts 

 of prey, that one which bv means of his bodily strength is best able to 

 struggle with his competitors for his prey is best provided in times of 

 limited food-supply, iluch more common is the unconscious struggle: 

 each man who attains a more favorable position bv special intelligence 

 and energy, limits to an equal degree the conditions of life for many of his 

 fellow men, however much he may interest himself in humanity. The 

 prey, wliich by special craft or swiftness escapes the pursuer, turns the 

 enemy upon the less favored of its companions. It is noticeable Urat in 

 severe epidemics certain men do not fall victims to the disease, because 

 their organization lietter withstands infection. Elere the term ' survival 

 of tlie fittest,' which Spencer has adopted in preference to 'struggle for 

 existence,' is better. 



Instances of /lie S/niggle for Exisi'cncc. — Although the foregoing 

 sufiices to show that the struggle for existence plays a very prominent 

 role, yet on account of the importance of this feature it will be illustrated 

 by a few concrete examples. The brown rat [Miis Jeemnanns), which 

 swarmed out from Asia at the beginning of the eighteenth century, has 

 almost completely exterminated the black or house-rat {Miis rallns) in 

 Europe, and has made existence impossilile for it in other parts of the 

 world. Several I']uropean species of thistle have increased so enormously 

 in the La Plata states that they have in places completely crowded out tlie 

 native plants. Another liuropean plant {Ilypoclnvris radicala) has 

 become a weed, overrunning everything in New Zealand. Certain races 

 of men, like the Dravidian and Indian, die oft" to the same degree that 

 other races of men, like the Caucasian, IMongolian, and Negro, spread. 

 The more one attempts to explain that cntllessly com]ilicated web of the 

 relations of animals to one another, the relations of animals to plants and 

 to climatic conditions, as Darwin has done, so much the more does he 



