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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。 Darwin has drawn attention to； and called the
〃STRUGGLE FOR EXISTENCE〃； and I have taken this simple case of a plant
because some people imagine that the phrase seems to imply a sort of
fight。
I have taken this plant and shown you that this is the result of the
ratio of the increase； the necessary result of the arrival of a time
coming for every species when exactly as many members must be destroyed
as are born； that is the inevitable ultimate result of the rate of
production。 Now； what is the result of all this？ I have said that
there are forty…nine struggling against every one； and it amounts to
this； that the smallest possible start given to any one seed may give
it an advantage which will enable it to get ahead of all the others；
anything that will enable any one of these seeds to germinate six hours
before any of the others will； other things being alike； enable it to
choke them out altogether。 I have shown you that there is no
particular in which plants will not vary from each other； it is quite
possible that one of our imaginary plants may vary in such a character
as the thickness of the integument of its seeds； it might happen that
one of the plants might produce seeds having a thinner integument； and
that would enable the seeds of that plant to germinate a little quicker
than those of any of the others； and those seeds would most inevitably
extinguish the forty…nine times as many that were struggling with them。
I have put it in this way； but you see the practical result of the
process is the same as if some person had nurtured the one and
destroyed the other seeds。 It does not matter how the variation is
produced； so long as it is once allowed to occur。 The variation in the
plant once fairly started tends to become hereditary and reproduce
itself； the seeds would spread themselves in the same way and take part
in the struggle with the forty…nine hundred； or forty…nine thousand；
with which they might be exposed。 Thus； by degrees； this variety； with
some slight organic change or modification； must spread itself over the
whole surface of the habitable globe； and extirpate or replace the
other kinds。 That is what is meant by NATURAL SELECTION； that is the
kind of argument by which it is perfectly demonstrable that the
conditions of existence may play exactly the same part for natural
varieties as man does for domesticated varieties。 No one doubts at all
that particular circumstances may be more favourable for one plant and
less so for another； and the moment you admit that； you admit the
selective power of nature。 Now； although I have been putting a
hypothetical case； you must not suppose that I have been reasoning
hypothetically。 There are plenty of direct experiments which bear out
what we may call the theory of natural selection； there is extremely
good authority for the statement that if you take the seed of mixed
varieties of wheat and sow it； collecting the seed next year and sowing
it again； at length you will find that out of all your varieties only
two or thre