The Conditions of Existence as Affecting the Perpetuation of Living Beings | Page 8

case of the last the breadth would be about
seven-tenths, and in the other it would be nine-tenths of the total length.
So that you see there is abundant evidence of variation among men in
their natural condition. And if you turn to other animals there is just the
same thing. The fox, for example, which has a very large geographical
distribution all over Europe, and parts of Asia, and on the American
Continent, varies greatly. There are mostly large foxes in the North,
and smaller ones in the South. In Germany alone, the foresters reckon
some eight different sorts.
Of the tiger, no one supposes that there is more than one species; they
extend from the hottest parts of Bengal, into the dry, cold, bitter steppes
of Siberia, into a latitude of 50 degrees,--so that they may even prey
upon the reindeer. These tigers have exceedingly different
characteristics, but still they all keep their general features, so that 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 means--given 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;