The Conditions of Existence as Affecting the Perpetuation of Living Beings | Page 9

by
which I mean the conditions which depend upon the state of the rest of
the organic creation, upon the number and kind of living beings, with
which an animal is surrounded. You may class these under two heads:
there are organic beings, which operate as 'opponents', and there are

organic beings which operate as 'helpers' to any given organic creature.
The opponents may be of two kinds: there are the 'indirect opponents',
which are what we may call 'rivals'; and there are the 'direct opponents',
those which strive to destroy the creature; and these we call 'enemies'.
By rivals I mean, of course, in the case of plants, those which require
for their support the same kind of soil and station, and, among animals,
those which require the same kind of station, or food, or climate; those
are the indirect opponents; the direct opponents are, of course, those
which prey upon an animal or vegetable. The 'helpers' may also be
regarded as direct and indirect: in the case of a carnivorous animal, for
example, a particular herbaceous plant may in multiplying be an
indirect helper, by enabling the herbivora on which the carnivore preys
to get more food, and thus to nourish the carnivore more abundantly;
the direct helper may be best illustrated by reference to some parasitic
creature, such as the tape-worm. The tape-worm exists in the human
intestines, so that the fewer there are of men the fewer there will be of
tape-worms, other things being alike. It is a humiliating reflection,
perhaps, that we may be classed as direct helpers to the tape-worm, but
the fact is so: we can all see that if there were no men there would be
no tape-worms.
It is extremely difficult to estimate, in a proper way, the importance and
the working of the Conditions of Existence. I do not think there were
any of us who had the remotest notion of properly estimating them until
the publication of Mr. Darwin's work, which has placed them before us
with remarkable clearness; and I must endeavour, as far as I can in my
own fashion, to give you some notion of how they work. We shall find
it easiest to take a simple case, and one as free as possible from every
kind of complication.
I will suppose, therefore, that all the habitable part of this globe--the
dry land, amounting to about 51,000,000 square miles,--I will suppose
that the whole of that dry land has the same climate, and that it is
composed of the same kind of rock or soil, so that there will be the
same station everywhere; we thus get rid of the peculiar influence of
different climates and stations. I will then imagine that there shall be
but one organic being in the world, and that shall be a plant. In this we
start fair. Its food is to be carbonic acid, water and ammonia, and the
saline matters in the soil, which are, by the supposition, everywhere

alike. We take one single plant, with no opponents, no helpers, and no
rivals; it is to be a "fair field, and no favour". Now, I will ask you to
imagine further that it shall be a plant which shall produce every year
fifty seeds, which is a very moderate number for a plant to produce;
and that, by the action of the winds and currents, these seeds shall be
equally and gradually distributed over the whole surface of the land. I
want you now to trace out what will occur, and you will observe that I
am not talking fallaciously any more than a mathematician does when
he expounds his problem. If you show that the conditions of your
problem are such as may actually occur in nature and do not transgress
any of the known laws of nature in working out your proposition, then
you are as safe in the conclusion you arrive at as is the mathematician
in arriving at the solution of his problem. In science, the only way of
getting rid of the complications with which a subject of this kind is
environed, is to work in this deductive method. What will be the result,
then? I will suppose that every plant requires one square foot of ground
to live upon; and the result will be that, in the course of nine years, the
plant will have occupied every single available spot in the whole globe!
I have chalked upon the blackboard the figures by which I arrive at the
result:-
Plants. Plants 1 x 50 in 1st year = 50 50 x 50 " 2nd " = 2,500 2,500 x 50
" 3rd " = 125,000 125,000 x 50 " 4th " = 6,250,000 6,250,000 x 50 "
5th " = 312,500,000 312,500,000 x 50