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there is no doubt as to their being tigers。 The Siberian tiger has a
thick fur； a small mane； and a longitudinal stripe down the back； while
the tigers of Java and Sumatra differ in many important respects from
the tigers of Northern Asia。 So lions vary； so birds vary； and so； if
you go further back and lower down in creation； you find that fishes
vary。 In different streams； in the same country even； you will find
the trout to be quite different to each other and easily recognisable by
those who fish in the particular streams。 There is the same
differences in leeches； leech collectors can easily point out to you
the differences and the peculiarities which you yourself would probably
pass by； so with fresh…water mussels； so； in fact； with every animal
you can mention。
In plants there is the same kind of variation。 Take such a case even as
the common bramble。 The botanists are all at war about it； some of them
wanting to make out that there are many species of it； and others
maintaining that they are but many varieties of one species； and they
cannot settle to this day which is a species and which is a variety！
So that there can be no doubt whatsoever that any plant and any animal
may vary in nature； that varieties may arise in the way I have
described；as spontaneous varieties；and that those varieties may be
perpetuated in the same way that I have shown you spontaneous varieties
are perpetuated； I say； therefore； that there can be no doubt as to the
origin and perpetuation of varieties in nature。
But the question now is：Does selection take place in nature？ is there
anything like the operation of man in exercising selective breeding；
taking place in nature？ You will observe that； at present； I say
nothing about species； I wish to confine myself to the consideration of
the production of those natural races which everybody admits to exist。
The question is； whether in nature there are causes competent to
produce races； just in the same way as man is able to produce by
selection； such races of animals as we have already noticed。
When a variety has arisen； the CONDITIONS OF EXISTENCE are such as to
exercise an influence which is exactly comparable to that of artificial
selection。 By Conditions of Existence I mean two things；there are
conditions which are furnished by the physical； the inorganic world；
and there are conditions of existence which are furnished by the
organic world。 There is； in the first place； CLIMATE； under that head
I include only temperature and the varied amount of moisture of
particular places。 In the next place there is what is technically
called STATION； which meansgiven the climate； the particular kind of
place in which an animal or a plant lives or grows； for example； the
station of a fish is in the water； of a fresh…water fish in fresh
water； the station of a marine fish is in the sea； and a marine animal
may have a station higher or deeper。 So again with land animals： the
differences in their stations are those of different soils and
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 oc