Survival of the Fittest. 43 r 



own eggs or young, a small number may be produced, and 

 the average stock be kept up ; but if many eggs or young^ 

 are destroyed, then many must be produced or the species 

 will become extinct. Therefore, the average number of any 

 animal or plant depends, though only indirectly, upon the 

 number of its eggs or seeds. We should never forget, in 

 taking a survey of nature, that every single organic being 

 around us may be said to be striving to the utmost to aug- 

 ment its members ; that each lives by a struggle at some 

 period of its existence, and that heavy destruction falls either 

 on the young or old during each generation or at recurrent 

 intervals. Let any check be lightened, or the destruction be 

 mitigated ever so little, and the number of the species will 

 almost instantaneously increase to any extent. 



But of the nature of the checks to increase we know little, 

 although this subject has been very ably treated by writers 

 of eminence, Eggs or very young animals seem geneially 

 to suffer the most, but this is not invariably the case. 

 While there is a vast destruction of the seeds of plants, but 

 it is the seedlings which are believed to suffer the greatest, 

 from germinating in ground already thickly stocked with 

 other plants, and from being destroyed in large numbers by 

 various enemies. The amount of food for each species of 

 course determines the extreme limit to which each can 

 increase, but very often it is not the obtaining of food, but the 

 serving as prey to other animals which fixes the average 

 number of a species. Thus there seems to be little doubt 

 that the stock of partridges, grouse and hares on any large 

 estate depends mainly on the destruction of vermin. Were 

 not a single head of game shot during the next twenty 

 years in England, says Darwin in substance, and no ver- 

 min were at the same time destroyed, there would in 

 all probability be less game than at present exists, although 

 hundreds of thousands of game animals are now annually 

 killed for the market. In some cases, on the other hand, 

 as in the case of the elephant, none are destroyed by 



