66 HIGH RATE OF INCREASE. Chap. III. 



conditions, a whole district, let it be ever so large. The 

 condor lays a couple of eggs and the ostrich a score, and 

 yet in the same country the condor may be the more 

 numerous of the two : the Fulmar petrel lays but one 

 egg, yet it is believed to be the most numerous bird 

 in the world. One fly deposits hundreds of eggs, and 

 another, like the hippobosca, a single one ; but this 

 difference does not determine how many individuals of 

 the two species can be supported in a district. A large 

 number of eggs is of some importance to those species, 

 which depend on a rapidly fluctuating amomit of food, 

 for it allows them rapidly to increase in number. But 

 the real importance of a large number of eggs or seeds 

 is to make up for much destruction at some period of 

 life ; 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 produced, and 

 yet the average stock be fully kept up; but if many 

 eggs or young are destroyed, many must be produced, 

 or the species will become extinct. It would suffice 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 be ensured to germi- 

 nate 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 foregoing considerations always in mind — never to 

 forget that every single organic being around us may 

 be said to be striving to the utmost to increase in num- 

 bers ; that each lives by a struggle at some period of 

 its life; that heavy destruction inevitably falls either 

 on the young or old, during each generation or at 

 recurrent intervals. Lighten any check, mitigate the 



