ould be requisite to produce nineteen million
elephants; a century or two more and there would be no standing room for
the latest generation of elephants. It is only too obvious that such a
result is not realized in nature, but it is on account of other natural
checks, and not because the natural rate of reproductive increase is
anything but excessive.

The third element of the process of natural selection is the struggle for
existence which is to a large extent the direct consequence of
over-multiplication. Because nature brings more individuals into existence
than it can support, every animal is involved in many-sided battles with
countless foes, and the victory is sometimes with one and sometimes with
another participant in the conflict. A survivor turns from one vanquished
enemy only to find itself engaged in mortal combat with other attacking
forces. Wherever we look, we find evidence of an unceasing struggle for
life, and an apparently peaceful meadow or pond is often the scene of
fierce battles and tragic death that escape our notice only because the
contending armies are dumb.

A community of ants, often comprising more individuals than an entire
European state, depends for its national existence upon its ability to
prevail over other communities with which it may engage in sanguinary wars
where the losses of a single battle may exceed those of Gettysburg. The
developing conger-eels find a host of enemies which greatly deplete their
numbers before they can grow even into infancy. An annual plant does not
produce a million living offspring in twenty years because seeds do not
always fall upon favorable soil, nor do they always receive the proper
amount of sunlight and moisture, or escape the eye of birds and other
seed-eating animals. These three illustrations bring out the fact that
there are three classes of natural conditions which must be met by every
living creature if it is to succeed in life. In detail, the struggle for
existence is _intra-specific_, involving some form of competition or
rivalry among the members of a single species; it is _inter-specific_, as
a conflict is waged by every species with other kinds of living things;
and finally it involves an adjustment of life to _inorganic environmental_
influences. While it may seem unjustifiable to speak of heat and cold and
sunlight as enemies, the direct effects produced by these forces are to be
reckoned with no less certainty than the attacks of livi