of opinion, a balancing of probabilities, in
which each man judges according to his lights,
the tone of his mind, and the inferences which
his previous notions lead him to draw from the
premises before him. Two men may arrive at
contrary opinions, both reasoning with perfect
sincerity of heart and desire for truth, For
instance, while Mr. Darwin holds that the world
has been desolated by no past cataclysm and
need apprehend no future one (which is contrary
to the universal tradition and belief of civilised
nations), M. Boutigny, a savant, of high rank in
his own country, asserts, with specious and
plausible argument, not only that the moon was
shot out by a convulsive explosion from the
earth, but that our planet may any day be seized
with the throes of a universal earthquake which
shall end in the expulsion of a second satellite;
in which case, every living thing must be
destroyed by fire. No cataclysm! Why
Messieurs Adhémar and Lehon, distinguished men
of science, believe that they have proved that a
grand deluge must inevitably devastate the globe
every ten thousand five hundred years;* that
such deluges have regularly occurred during all
previous time, and that such will recur again at
their stated epochs; and that, although these
grand deluges may not be so universal as to
desolate the whole world, they are cataclysms
sufficiently terrific to exterminate the great
majority of existing creatures, and to render a fresh
act of creation an event at least desirable and
called for by circumstances.

To return to the theory by which independent
creations are obviated. Nature is most prodigal
in conferring life. More individuals of every
kind, both plants and animals, are produced
than can possibly survive, and there must in
every case be a contest for life; either
between individuals of the same species, or
between the individuals of distinct species. It
is Malthus's doctrine applied to the whole
animal and vegetable kingdoms, with increased
force; for, in this case, there can be no
artificial increase of food, and no prudential
restraint from marriage. Although some species
may be now increasing more or less rapidly in
numbers, all cannot so increase, for the world
would not hold them. There is no exception to the
rule that every organic being naturally increases
at so high a rate, that, if not destroyed, the earth
would soon be covered by the progeny of a
single pair. Even slow-breeding man has
doubled in twenty-five years; and at this rate,
in a few thousand years there would literally not
be standing-room for his progeny. Linnaeus has
calculated that if an annual plant produced only
two seeds—and there is no plant so unproductive
as this—and their seedlings next year
produced two, and so on, then, in twenty years,
there would be a million of plants.

* See All the Year Round, No. 52, p. 40.

As a consequence, the weakest goes to the
wall; it is a race for life, with the deuce
taking the hindmost. A grain in the balance
will determine which individual shall live and
which shall die: which variety or species shall
increase in number, and which shall decrease,
or finally become extinct. The slightest
advantage in one being, at any age or during
any season, over those with which it comes
into competition, or any better adaptation in
however slight a degree to the surrounding
physical conditions, will tend to the preservation
of that individual, and will generally be
inherited by its offspring. The offspring, also, will
thus have a better chance of surviving, for, of
the many individuals of any species which are
periodically born, but a small number can
survive. This is Natural Selection—a power which
acts during long ages, rigidly scrutinising the
whole constitution, structure, and habits of each
creature— favouring the good and rejecting the
bad. Though nature grants vast periods of time
for the work of natural selection, she does not
grant an indefinite period; for as all organic
beings are striving, it may be said, to seize on
each place in the economy of nature, if any one
species does not become modified and improved
in a corresponding degree with its competitors,
it will soon be exterminated.

Cases of adaptation which have hitherto been
attributed to design and contrivance are by this
theory regarded as the result of natural selection
only. When we see leaf-eating insects green,
and bark-feeders mottled grey, the Alpine
ptarmigan white in winter, the red grouse the colour
of heather, and the black grouse that of peaty
earth, we must believe that those tints are of
service to these birds and insects in preserving
them from danger. Grouse, if not destroyed at
some period of their lives, would increase in
countless numbers—they are known to suffer
largely from birds of prey; and hawks are
guided by eyesight to their prey—so much so,
that on parts of the Continent persons are warned
not to keep white pigeons, as being the most
liable to destruction. Hence Mr. Darwin can
see no reason to doubt that Natural Selection
might be effective in giving the proper colour
to each kind of grouse, and in keeping that
colour, when once acquired, true and constant.

To make it clear how Natural Selection acts,
an imaginary illustration is given. Let us take
the case of a wolf, which preys on various
animals, securing some by craft, some by
strength, and some by fleetness; and let us
suppose that the fleetest prey, a deer, for
instance, had from any change in the country
increased in numbers, or that other prey had
decreased in numbers, during that season of the
year when the wolf is hardest pressed for food.
Under such circumstances, there is no reason to
doubt that the swiftest and slimmest wolves
would have the best chance of surviving, and
so be preserved or selected— provided always
that they retained strength to master their prey
at this or some other period of the year, when
they might be compelled to prey on other
animals. There seems no more reason to doubt
this, than that man can improve the fleetness
of his greyhounds by methodical selection, or
by that unconscious selection which results from