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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 survival of the fittest or the preservation of favoured races in the struggle for life, new species may be originated.
This self-acting process which, by means of a few easily demonstrated groups of facts, brings about change in the organic world, and keeps each species in harmony with the conditions of its existence, will appear to some persons so clear and simple as to need no further demonstration. But to the great majority of naturalists and men of science endless difficulties and objections arise, owing to the wonderful variety of animal and vegetable forms, and the intricate relations of the different species and groups of species with each other ; and it was to answer as many of these objections as possible, and to show that the more we know of nature the more we
find it to harmonise with the development hypothesis, that Darwin devoted the whole of his life to collecting facts and making experiments, the record of a portion of which he has given us in a series of twelve masterly volumes.
Proposed Mode of Treatment of the Subject. It is evidently of the most vital importance to any theory that its foundations should be absolutely secure. It is therefore necessary to show, by a wide and comprehensive array of facts, that animals and plants do perpetually vary in the manner and to the amount requisite ; and that this takes place in wild animals as well as in those which are domesticated. It is necessary also to prove that all organisms do tend to increase at the great rate alleged, and that this increase actually occurs, under favourable conditions. We have to prove, further, that variations of all kinds can be increased and accumulated by selection; and that the struggle for existence to the extent here indicated actually occurs in nature, and leads to the continued preservation of favourable variations.
These matters will be discussed in the four succeeding chapters, though in a somewhat different order—the struggle for existence and the power of rapid multiplication, which is its cause, occupying the first place, as comprising those facts which are the most fundamental and those which can be perfectly explained without any reference to the less generally understood facts of variation. These chapters will be followed by a discussion of certain difficulties, and of the vexed question of hybridity. Then will come a rather full account of the more important of the complex relations of organisms to each other and to the earth itself, which are either fully explained or greatly elucidated by the theory. The concluding chapter will treat of the origin of man and his relations to the lower animals.
THE STRUGGLE FOR EXISTENCE
Its importance-The struggle among plants- Among animals—Illustrative
cases — Succession of trees in forests of Denmark — The struggle for existence on the Pampas – Increase of organisms in a geometrical ratio – Examples of great powers of increase of animals— Rapid increase and wide spread of plants - Great fertility not essential to rapid increase-Struggle between closely allied species most severeThe ethical aspect of the struggle for existence.
THERE is perhaps no phenomenon of nature that is at once so important, so universal, and so little understood, as the struggle for existence continually going on among all organised beings. To most persons nature appears calm, orderly, and peaceful. They see the birds singing in the trees, the insects hovering over the flowers, the squirrel climbing among the tree-tops, and all living things in the possession of health and vigour, and in the enjoyment of a sunny existence. But they do not see, and hardly ever think of, the means by which this beauty and harmony and enjoyment is brought about. They do not see the constant and daily search after food, the failure to obtain which means weakness or death ; the constant effort to escape enemies ; the ever-recurring struggle against the forces of nature. This daily and hourly struggle, this incessant warfare, is nevertheless the very means by which much of the beauty and harmony and enjoyment in nature is produced, and also affords one of the most important elements in bringing about the origin of species. We must, therefore, devote some time to the consideration of its various aspects and of the many curious phenomena to which it gives rise.
It is a matter of common observation that if weeds are allowed to grow unchecked in a garden they will soon destroy
a number of the flowers. It is not so commonly known that if a garden is left to become altogether wild, the weeds that first take possession of it, often covering the whole surface of the ground with two or three different kinds, will themselves be supplanted by others, so that in a few years many of the original flowers and of the earliest weeds may alike have disappeared. This is one of the very simplest cases of the struggle for existence, resulting in the successive displacement of one set of species by another; but the exact causes of this displacement are by no means of such a simple nature. All the plants concerned may be perfectly hardy, all may grow freely from seed, yet when left alone for a number of years, each set is in turn driven out by a succeeding set, till at the end of a considerable period -a century or a few centuries perhaps — hardly one of the plants which first monopolised the ground would be found there.
Another phenomenon of an analogous kind is presented by the different behaviour of introduced wild plants or animals into countries apparently quite as well suited to them as those which they naturally inhabit. Agassiz, in his work on Lake Superior, states that the roadside weeds of the northeastern United States, to the number of 130 species, are all European, the native weeds having disappeared westwards ; and in New Zealand there are no less than 250 species of naturalised European plants, more than 100 species of which have spread widely over the country, often displacing the native vegetation. On the other hand, of the many hundreds of hardy plants which produce seed freely in our gardens, very few ever run wild, and hardly any have become common. Even attempts to naturalise suitable plants usually fail; for A. de Candolle states that several botanists of Paris, Geneva, and especially of Montpellier, have sown the seeds of many hundreds of species of hardy exotic plants in what appeared to be the most favourable situations, but that, in hardly a single case, has any one of them become naturalised. Even a plant like the potato—so widely cultivated, so hardy, and so well adapted to spread by means of its many-eyed tubers—has not established itself in a wild state in any part of Europe. It would be thought that Australian plants would easily run
1 Géographie Botanique, p. 798.
wild in New Zealand. But Sir Joseph Hooker informs us that the late Mr. Bidwell habitually scattered Australian seeds during his extensive travels in New Zealand, yet only two or three Australian plants appear to have established themselves in that country, and these only in cultivated or newly moved
These few illustrations sufficiently show that all the plants of a country are, as De Candolle says, at war with each other, each one struggling to occupy ground at the expense of its neighbour. But, besides this direct competition, there is one not less powerful arising from the exposure of almost all plants to destruction by animals. The buds are destroyed by birds, the leaves by caterpillars, the seeds by weevils; some insects bore into the trunk, others burrow in the twigs and leaves ; slugs devour the young seedlings and the tender shoots, wireworms gnaw the roots. Herbivorous mammals devour many species bodily, while some uproot and devour the buried tubers.
In animals, it is the eggs or the very young that suffer most from their various enemies; in plants, the tender seedlings when they first appear above the ground. To illustrate this latter point Mr. Darwin cleared and dug a piece of ground three feet long and two feet wide, and then marked all the seedlings of weeds and other plants which came up, noting what became of them. The total number was 357, and out of these no less than 295 were destroyed by slugs and insects. The direct strife of plant with plant is almost equally fatal when the stronger are allowed to smother the weaker. When turf is mown or closely browsed by animals, a number of strong and weak plants live together, because none are allowed to grow much beyond the rest ; but Mr. Darwin found that when the plants which compose such turf are allowed to grow up freely, the stronger kill the weaker. In a plot of turf three feet by four, twenty distinct species of plants were found to be growing, and no less than nine of these perished altogether when the other species were allowed to grow up to their full size.?
But besides having to protect themselves against competing plants and against destructive animals, there is a yet deadlier
i The Origin of Species, p. 53.