66 
HIGH BATE OF INCKEASE. 
Chap. III. 
produce eggs or seeds by the thousand, and those which 
produce extremely few, is, that the slow-breeders would 
require a few more years to people, under favourable 
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 an¬ 
other, like the hippobosca, a single one; but this differ¬ 
ence 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 amount 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 
tlie 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 
