EVOLUTION AND NATURAL SELECTION 7 



a ratio that no district, no station, not even the whole sur- 

 face of the land or the whole ocean would hold the progeny 

 of a single pair after a certain number of generations. Even 

 slow-breeding man has doubled in twenty-five years, and at 

 this rate, in less than a thousand years, there would literally 

 not be standing room for his progeny. In the same way all 

 through nature every organic being may be said to be striv- 

 ing to the utmost to increase its numbers. The result is an 

 ever recurrent struggle for existence. It has been truly said 

 that all nature is at war. The strongest ultimately prevail, 

 the weakest fail, and we well know that myriads of forms have 

 disappeared from the face of the earth." Here we again recall 

 the classic words of Darwin: "When we look at the plants and 

 bushes clothing an entangled bank, we are tempted to attribute 

 their proportional number and kind to what we call chance. 

 But how false a view this is. What a struggle must have gone 

 on during long centuries between different kinds of trees, each 

 annually scattering its seeds by the thousand. What war 

 between insect and insect, between insects, snails, and other 

 animals, with birds and beasts of prey all striving to increase, 

 all feeding on each other or on the trees, their seeds and seed- 

 lings, or on the other plants which first clothed the ground and 

 thus checked the growth of the trees. But the struggle will 

 almost invariably be more severe between the individuals of 

 the same species, as they frequent the same districts, require 

 the same food, and are exposed to the same dangers." 



He further maintained that in all nature we see a strong 

 tendency to variation. Now if any organic being varies even 

 in a slight degree owing to change in environment, of which we 

 have abundant geological evidence: if in the long course of 

 ages inheritable variations ever arise in any way advantageous 

 to any being under its exceedingly complex and changing rela- 

 tions of life, it would be a strange fact if beneficial variations 

 never arose, seeing how many have arisen which man has taken 

 advantage of for his own profit and pleasure. If, then, these 

 contingencies ever occur, then the ever recurrent struggle for 

 existence will determine that those variations, however slight, 

 which are favorable shall be preserved or selected, and those 

 which are unfavorable shall be destroyed, and from the strong 



