Darwinism | Page 9

that they are sure to be appreciated
by every one who takes an interest in nature, but unless the need of
them is clearly seen it may be thought that time is being wasted on
mere curious details and strange facts which have little bearing on the
question at issue.
The theory of natural selection rests on two main classes of facts which
apply to all organised beings without exception, and which thus take
rank as fundamental principles or laws. The first is, the power of rapid
multiplication in a geometrical progression; the second, that the
offspring always vary slightly from the parents, though generally very
closely resembling them. From the first fact or law there follows,
necessarily, a constant struggle for existence; because, while the
offspring always exceed the parents in number, generally to an
enormous extent, yet the total number of living organisms in the world
does not, and cannot, increase year by year. Consequently every year,
on the average, as many die as are born, plants as well as animals; and
the majority die premature deaths. They kill each other in a thousand
different ways; they starve each other by some consuming the food that
others want; they are destroyed largely by the powers of nature--by
cold and heat, by rain and storm, by flood and fire. There is thus a
perpetual struggle among them which shall live and which shall die;
and this struggle is tremendously severe, because so few can possibly
remain alive--one in five, one in ten, often only one in a hundred or
even one in a thousand.
Then comes the question, Why do some live rather than others? If all
the individuals of each species were exactly alike in every respect, we
could only say it is a matter of chance. But they are not alike. We find
that they vary in many different ways. Some are stronger, some swifter,

some hardier in constitution, some more cunning. An obscure colour
may render concealment more easy for some, keener sight may enable
others to discover prey or escape from an enemy better than their
fellows. Among plants the smallest differences may be useful or the
reverse. The earliest and strongest shoots may escape the slug; their
greater vigour may enable them to flower and seed earlier in a wet
autumn; plants best armed with spines or hairs may escape being
devoured; those whose flowers are most conspicuous may be soonest
fertilised by insects. We cannot doubt that, on the whole, any beneficial
variations will give the possessors of it a greater probability of living
through the tremendous ordeal they have to undergo. There may be
something left to chance, but on the whole the fittest will survive.
Then we have another important fact to consider, the principle of
heredity or transmission of variations. If we grow plants from seed or
breed any kind of animals year after year, consuming or giving away all
the increase we do not wish to keep just as they come to hand, our
plants or animals will continue much the same; but if every year we
carefully save the best seed to sow and the finest or brightest coloured
animals to breed from, we shall soon find that an improvement will
take place, and that the average quality of our stock will be raised. This
is the way in which all our fine garden fruits and vegetables and
flowers have been produced, as well as all our splendid breeds of
domestic animals; and they have thus become in many cases so
different from the wild races from which they originally sprang as to be
hardly recognisable as the same. It is therefore proved that if any
particular kind of variation is preserved and bred from, the variation
itself goes on increasing in amount to an enormous extent; and the
bearing of this on the question of the origin of species is most
important. For if in each generation of a given animal or plant the fittest
survive to continue the breed, then whatever may be the special
peculiarity that causes "fitness" in the particular case, that peculiarity
will go on increasing and strengthening _so long as it is useful to the
species_. But the moment it has reached its maximum of usefulness,
and some other quality or modification would help in the struggle, then
the individuals which vary in the new direction will survive; and thus a
species may be gradually modified, first in one direction, then in

another, till it differs from the original parent form as much as the
greyhound differs from any wild dog or the cauliflower from any wild
plant. But animals or plants which thus differ in a state of nature are
always classed as distinct species, and thus we see how, by the
continuous