43 o Life and Immortality. 



supposes that their fertility has been increased in any 

 sensible degree by change of habitat, the obvious explana- 

 tion being that the conditions of environment have been 

 very favorable, and that there has consequently been less 

 destruction of old and young, and that nearly all the latter 

 have been enabled to breed. The extraordinarily rapid 

 increase and wide diffusion of naturalized productions in 

 new homes, a result which never fails to evoke surprise, is 

 only to be explained on the principle of the Geometrical 

 Ratio of Increase. As in nature almost every plant produces 

 seed, and there are very few animals that do not annually 

 pair, therefore we can confidently assert that all plants and 

 animals are tending to increase in a geometrical ratio ; that 

 all would most rapidly stock every station in which they 

 could in any way exist, and that the tendency to increase 

 must be checked by destruction at some period of life. 

 Among our larger domestic animals we see no great 

 destruction falling on them. We forget that thousands are 

 annually slaughtered for food, and that in a natural state an 

 equal number would have to be disposed of in some way or 

 other. Between organisms which annually produce seeds or 

 eggs by the thousands, and those which produce extremely 

 few, the only difference is that the slow breeders would 

 require a few more years to people, under favorable con- 

 ditions, a whole district, let it be ever so large. But a couple 

 of eggs are laid by the condor, while the ostrich lays a score. 

 Yet in the same country the condor may be the more abun- 

 dant of the two. The Fulmer petrel lays but a single egg, 

 yet it is believed to be the most numerous bird in the world. 

 A large number of eggs is of some importance to those 

 species which depend upon a rapidly-fluctuating quantity of 

 food, for it permits them to increase rapidly in number ; but 

 the real importance of a large number of eggs or seeds is to 

 make up for the great destruction that goes on at some 

 period of life, and this period in the vast majority of cases 

 is an early one. If an animal can in any way protect its 



