the conditions of existence-第4章
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neighbourhoods； some being best adapted to a calcareous； and others to
an arenaceous soil。 The third condition of existence is FOOD； by which
I mean food in the broadest sense； the supply of the materials necessary
to the existence of an organic being； in the case of a plant the
inorganic matters； such as carbonic acid； water； ammonia； and the
earthy salts or salines； in the case of the animal the inorganic and
organic matters； which we have seen they require； then these are all；
at least the two first； what we may call the inorganic or physical
conditions of existence。 Food takes a mid…place； and then come the
organic conditions； 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
globethe 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 〃 6th 〃 = 15；625；000；000
15；625；000；000 x 50 〃 7th 〃 = 781；250；000；000
781；250；000；000 x 50 〃 8th 〃 = 39；062；500；000；000
39；062；500；000；000 x 50& 〃 9th 〃 = 1；953；125；000；000；000
51；000；000 sq。 milesthe dry surface of the earth x 27；878；400the
number of sq。 ft。 in 1 sq。 mile = sq。 ft。 1；421；798；400；000；000 being
531；326；600；000；000 square feet less than would be required at the end
of the ninth year。
You will see from this that； at the end of the first year the single
plant will have produced fifty more of its kind； by the end of the
second year these will have increased to 2；500； and so on； in
succeeding years； you get beyond even trillions； and I am not at all
sure that I could tell you what the proper arithmetical denomination of
the total number really is； but； at any rate； you will understand the
meaning of all those noughts。 Then you see that； at the bottom； I have
taken the 51；000；000 of square miles； constituting the surface of the
dry land； and as the number of square feet are placed under and
subtracted from the number of seeds that would be produced in the ninth
year； you can see at once that there would be an immense number more of
plants than there would be square feet of ground for their
accommodation。 This is certainly quite enough to prove my point； that
between the eighth and ninth year after being planted the single plant
would have stocked the whole available surface of the earth。
This is a thing which is hardly conceivableit seems hardly
imaginableyet it is so。 It is indeed simply the law of Malthus
exemplified。 Mr。 Malthus was a clergyman； who worked out this subject
most minutely and truthfully some years ago； he showed quite
clearly；and although he was much abused for his conclusions at the
time； they have never yet been disproved and never will behe showed
that in consequence of the increase in the number of organic beings in
a geometrical ratio； while the means of existence cannot be made to
increase in the same ratio； that there must come a time when the number
of organic beings will be in excess of the power of production of
nutriment； and that thus some check must arise to the further increase
of those organic beings。 At the end of the ninth year we have seen that
each plant would not be able to get its full square foot of ground； and
at the end of another year it would have to share that space with fifty
others the produce of the seeds which it would give off。
What； then； takes place？ Every plant grows up； flourishes； occupies its
square foot of ground； and gives off its fifty seeds； but notice this；
that out of this number only one can come to anything； there is thus；
as it were； forty…nine chances to one against its growing up； it
depends upon the most fortuitous circumstances whether any one of these
fifty seeds shall grow up and flourish； or whether it shall die and
perish。 This is what Mr。
