18 THE DARWINIAN HYPOTHESIS i 



live at the expense of some other animal or plant, 

 but the very plants are at war. The ground is 

 full of seeds that cannot rise into seedlings ; the 

 seedlings rob one another of air, light and water, 

 the strongest robber winning the day, and ex- 

 tinguishing his competitors. Year after year, the 

 wild animals with which man never interferes are, 

 on the average, neither more nor less numerous 

 than they were ; and yet we know that the annual 

 produce of every pair is from one to perhaps a 

 million young ; so that it is mathematically certain 

 that, on the average, as many are killed by natural 

 causes as are born every year, and those only escape 

 which happen to be a little better fitted to resist 

 destruction than those which die. The individuals 

 of a species are like the crew of a foundered ship, 

 and none but good swimmers have a chance of 

 reaching the land. 



Such being unquestionably the necessary con- 

 ditions under which living creatures exist, Mr. 

 Darwin discovers in them the instrument of natural 

 selection. Suppose that in the midst of this in- 

 cessant competition some individuals of a species 

 (A) present accidental variations which happen to 

 fit them a little better than their fellows for the 

 struggle in which they are engaged, then the 

 chances are in favour, not only of these individuals 

 being better nourished than the others, but of 

 their predominating over their fellows in other 

 ways, and of having a better chance of leaving 



