430 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 solarge. Butacouple 
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 
isan early one. If an animal can in any way protect its 
