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title varchar(250) 139 Column Stats
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475 rows, page 69 of 119 (4/p)
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03 - Struggle for Existence 03-01 - Bears on Natural Selection 20 Again, it may be asked, how is it that varieties, which I have called incipient species, become ultimately converted into good and distinct species which in most cases obviously differ from each other far more than do the varieties of the same species?

How do those groups of species, which constitute what are called distinct genera, and which differ from each other more than do the species of the same genus, arise?

All these results, as we shall more fully see in the next chapter, follow from the struggle for life.

Owing to this struggle, variations, however slight and from whatever cause proceeding, if they be in any degree profitable to the individuals of a species, in their infinitely complex relations to other organic beings and to their physical conditions of life, will tend to the preservation of such individuals, and will generally be inherited by the 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.

I have called this principle, by which each slight variation, if useful, is preserved, by the term Natural Selection, in order to mark its relation to man's power of selection.

But the expression often used by Mr. Herbert Spencer of the Survival of the Fittest is more accurate, and is sometimes equally convenient. We have seen that man by selection can certainly produce great results, and can adapt organic beings to his own uses, through the accumulation of slight but useful variations, given to him by the hand of Nature.

Herbert Spencer
Herbert Spencer


But Natural Selection, as we shall hereafter see, is a power incessantly ready for action, and is as immeasurably superior to man's feeble efforts, as the works of Nature are to those of Art.
03 - Struggle for Existence 03-02 - The Term, Struggle for Existence, used in a large sense 20 I should premise that I use this term in a large and metaphorical sense including dependence of one being on another, and including (which is more important) not only the life of the individual, but success in leaving progeny.

Two canine animals, in a time of dearth may be truly said to struggle with each other which shall get food and live.

canine
canine


But a plant on the edge of a desert is said to struggle for life against the drought, though more properly it should be said to produces a thousand seeds, of which only one of an average comes to maturity, may be more truly said to struggle with the plants of the same and other kinds which already clothe the ground.

The mistletoe is dependent on the apple and a few other trees, but can only in a far-fetched sense be said to struggle with these trees, for, if too many of these parasites grow on the same tree, it languishes and dies.

mistletoe
mistletoe

apple
apple


But several seedling mistletoes, growing close together on the same branch, may more truly be said to struggle with each other. As the mistletoe is disseminated by birds, its existence depends on them; and it may methodically be said to struggle with other fruit-bearing plants, in tempting the birds to devour and thus disseminate its seeds. In these several senses, which pass into each other, I use for convenience' sake the general term of Struggle for Existence.

mistletoe
mistletoe

bird
bird
03 - Struggle for Existence 03-03 - Geometrical Ratio of Increase 20 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.

Earth
Earth


Even slow-breeding man has doubled in twenty-five years, and at this rate, in less than a thousand years, there would literally not be standing-room for his progeny.

Ape Man
Ape Man


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 should be a million plants.

The elephant is reckoned the slowest breeder of all known animals, and I have taken some pains to estimate its probable minimum rate of natural increase; it will be safest to assume that it begins breeding when thirty years old, and goes on breeding till ninety years old, bringing forth six young in the interval, and surviving till one hundred years old; if this be so, after a period of from 740 to 750 years there would be nearly nineteen million elephants alive, descended from the first pair.

elephant
elephant

Orangutan
Orangutan
04 - Natural Selection 04-01 - Natural Selection 20 Variations neither useful nor injurious would not be affected by natural selection, and would be left either a fluctuating element, as perhaps we see in certain polymorphic species, or would ultimately become fixed, owing to the nature of the organism and the nature of the conditions.