74 NATURE OF THE CHECKS TO INCREASE. Chap. IIT, 



and this period in the great majority of cases is an early one. 

 If an animal can in any way protect its own eggs or young, a 

 small number may be i)roduccd, and yet the average stock be 

 fully kept up; ])ut if many eggs or young are dcstroj'ed, many 

 must be produced, or the species will become extinct. It 

 would suilicc to keep up the full number of a tree, which lived 

 on an average for a thousand years, if a single seed were pro- 

 duced once in a thousand years, supposing that this seed were 

 never destroyed, and Could lie insured to germinate in a fitting 

 place. So that, in all cases, the average number of any animal 

 or plant depends only indirectly on the number of its eggs or 

 seeds. 



In looking at Nature, it is most necessary to keep the fore- 

 going considerations always in mind — never to forget that 

 everj- single organic being around us may be said to be striving 

 to the utmost to increase in numbers ; that each lives by a 

 struggle at some period of its life ; that hea\'y destruction in- 

 evitably falls either on the young or old, during each genera- 

 tion or at recurrent intervals. Lighten any check, mitigate 

 the destruction ever so little, and the number of the species 

 will almost instantaneously increase to any amount. 



Nature of the Checks to Increase. 



The causes which check the natural tendency of each spe- 

 cies to increase are most obscure. Look at the most vigorous 

 species ; by as much as it swarms in numbers, by so much will 

 its tendency to increase be still further increased. We know 

 not exactly what the checks are in even one single instance. 

 Nor will this surprise any one who reflects hov/ ignorant we 

 are on this head, even in regard to mankind, so incomparably 

 better known than any other animal. This subject has been 

 alily treated by several authors, and I shall, in my future work, 

 discuss some of the checks at considerable length, more es- 

 pecially in regard to the feral animals of South America. Here 

 I will make only a few remarks, just to recall to the reader's 

 mind some of the chief points. Eggs or very young animals 

 seem genei-ally to sufler most, but this is not invariably the 

 case. "With plants there is a vast destruction of seeds, but, 

 from some observations which I have made, I believe that it 

 is the seedlings which sufier most from germinating in ground 

 iilrcvady thickly stocked with othcn- jilants. Seedlings, also, are 

 destroyed in vast numbers by various enemies ; for instance. 



