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|OriginOfSpecies - 475 Rows|
|14 - Recapitulation and Conclusion||14-01 - Recapitulation of the difficulties on the theory of Natural Selection||50||
As on the theory of natural selection an interminable number of intermediate forms must have existed, linking together all the species in each group by gradations as fine as our present varieties, it may be asked, Why do we not see these linking forms all around us?
Why are not all organic beings blended together in an inextricable chaos? With respect to existing forms, we should remember that we have no right to expect (excepting in rare cases) to discover directly connecting links between them, but only between each and some extinct and supplanted form.
Even on a wide area, which has during a long period remained continuous, and of which the climate and other conditions of life change insensibly in going from a district occupied by one species into another district occupied by a closely allied species, we have no just right to expect often to find intermediate varieties in the intermediate zone.
For we have reason to believe that only a few species are undergoing change at any one period; and all changes are slowly effected.
I have also shown that the intermediate varieties which will at first probably exist in the intermediate zones, will be liable to be supplanted by the allied forms on either hand; and the latter, from existing in greater numbers, will generally be modified and improved at a quicker rate than the intermediate varieties, which exist in lesser numbers; so that the intermediate varieties will, in the long run, be supplanted and exterminated.
On this doctrine of the extermination of an infinitude of connecting links, between the living and extinct inhabitants of the world, and at each successive period between the extinct and still older species, why is not every geological formation charged with such links?
Why does not every collection of fossil remains afford plain evidence of the gradation and mutation of the forms of life? We meet with no such evidence, and this is the most obvious and forcible of the many objections which may be urged against my theory.
Why, again, do whole groups of allied species appear, though certainly they often falsely appear, to have come in suddenly on the several geological stages?
Why do we not find great piles of strata beneath the Silurian system, stored with the remains of the progenitors of the Silurian groups of fossils? For certainly on my theory such strata must somewhere have been deposited at these ancient and utterly unknown epochs in the world's history.
I can answer these questions and grave objections only on the supposition that the geological record is far more imperfect than most geologists believe.
|14 - Recapitulation and Conclusion||14-03 - Causes of the general belief in the immutability of species||20||
Glancing at instincts, marvellous as some are, they offer no greater difficulty than does corporeal structure on the theory of the natural selection of successive, slight, but profitable modifications.
We can thus understand why nature moves by graduated steps in endowing different animals of the same class with their several instincts.
I have attempted to show how much light the principle of gradation throws on the admirable architectural powers of the hive-bee.
Habit no doubt sometimes comes into play in modifying instincts; but it certainly is not indispensable, as we see, in the case of neuter insects, which leave no progeny to inherit the effects of long-continued habit.
|14 - Recapitulation and Conclusion||14-02 - Recapitulation of the general and special circumstances in its favour||20||
There is no obvious reason why the principles which have acted so efficiently under domestication should not have acted under nature.
In the preservation of favoured individuals and races, during the constantly-recurrent Struggle for Existence, we see the most powerful and ever-acting means of selection.
The struggle for existence inevitably follows from the high geometrical ratio of increase which is common to all organic beings.
This high rate of increase is proved by calculation, by the effects of a succession of peculiar seasons, and by the results of naturalisation, as explained in the third chapter.
More individuals are born than can possibly survive.
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.
As the individuals of the same species come in all respects into the closest competition with each other, the struggle will generally be most severe between them; it will be almost equally severe between the varieties of the same species, and next in severity between the species of the same genus.
But the struggle will often be very severe between beings most remote in the scale of nature.
The slightest advantage in one being, at any age or during any season, over those with which it comes into competition, or better adaptation in however slight a degree to the surrounding physical conditions, will turn the balance.
With animals having separated sexes there will in most cases be a struggle between the males for possession of the females.
The most vigorous individuals, or those which have most successfully struggled with their conditions of life, will generally leave most progeny.
But success will often depend on having special weapons or means of defence, or on the charms of the males; and the slightest advantage will lead to victory.
|14 - Recapitulation and Conclusion||14-03 - Causes of the general belief in the immutability of species||50||
Lastly, the law of the long endurance of allied forms on the same continent, -- of marsupials in Australia, of edentata in America, and other such cases, -- is intelligible, for within a confined country, the recent and the extinct will naturally be allied by descent.