M Database Inspector (cheetah)
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|OriginOfSpecies - 475 Rows|
|04 - Natural Selection||04-02 - Its Power Compared with Man's Selection||20||
As man can produce, and certainly has produced, a great result by his methodical and unconscious means of selection, what may not natural selection effect?
Man can act only on external and visible characters: Nature, if I may be allowed to personify the natural preservation or survival of the fittest, cares nothing for appearances, except in so far as they are useful to any being.
She can act on every internal organ, on every shade of constitutional difference, on the whole machinery of life.
Man selects only for his own good: Nature only for that of the being which she tends. Every selected character is fully exercised by her, as is implied by the fact of their selection.
Man keeps the natives of many climates in the same country; he seldom exercises each selected character in some peculiar and fitting manner; he feeds a long and a short beaked pigeon on the same food; he does not exercise a long-backed or long-legged quadruped in any peculiar manner; he exposes sheep with long and short wool to the same climate.
He does not allow the most vigorous males to struggle for the females. He does not rigidly destroy all inferior animals, but protects during each varying season, as far as lies in his power, all his productions. He often begins his selection by some half-monstrous form; or at least by some modification prominent enough to catch the eye or to be plainly useful to him.
Under nature, the slightest differences of structure or constitution may well turn the nicely balanced scale in the struggle for life, and so be preserved. How fleeting are the wishes and efforts of man! how short his time! and consequently how poor will be his results, compared with those accumulated by Nature during whole geological periods!
Can we wonder, then, that Nature's productions should be far "truer" in character than man's productions; that they should be infinitely better adapted to the most complex conditions of life, and should plainly bear the stamp of far higher workmanship?
|05 - Laws of Variation||05-11 - Species of the Same Genus Vary in an Analogous Manner||20||
Many similar cases of analogous variation have been observed by Naudin in the great gourd-family, and by various authors in our cereals.
Similar cases occurring with insects under natural conditions have lately been discussed with much ability by Mr. Walsh, who has grouped them under his law of Equable Variability.
With pigeons, however, we have another case, namely, the occasional appearance in all the breeds, of slaty-blue birds with two black bars on the wings, white loins, a bar at the end of the tail, with the outer feathers externally edged near their basis with white.
As all these marks are characteristic of the parent rock-pigeon, I presume that no one will doubt that this is a case of reversion, and not of a new yet analogous variation appearing in the several breeds.
We may, I think, confidently come to this conclusion, because, as we have seen, these coloured marks are eminently liable to appear in the crossed offspring of two distinct and differently coloured breeds; and in this case there is nothing in the external conditions of life to cause the reappearance of the slaty-blue, with the several marks, beyond the influence of the mere act of crossing on the laws of inheritance.
|06 - Difficutiles in Theory||06-06 - Species with Habits Widely Diffferent from those of their Allies||20||
He who believes that each being has been created as we now see it, must occasionally have felt surprise when he has met with an animal having habits and structure not in agreement.
What can be plainer than that the webbed feet of ducks and geese are formed for swimming?
Yet there are upland geese with webbed feet which rarely go near the water; and no one except Audubon has seen the frigate-bird, which has all its four toes webbed, alight on the surface of the ocean.
On the other hand, grebes and coots are eminently aquatic, although their toes are only bordered by membrane.
What seems plainer than that the long toes, not furnished with membrane, of the Grallatores are formed for walking over swamps and floating plants?- the water-hen and landrail are members of this order, yet the first is nearly as aquatic as the coot, and the second nearly as terrestrial as the quail or partridge.
In such cases, and many others could be given, habits have changed without a corresponding change of structure.
The webbed feet of the upland goose may be said to have become almost rudimentary in function, though not in
In the frigate-bird, the deeply scooped membrane between the toes shows that structure has begun to change.
|06 - Difficutiles in Theory||06-03 - Absence or Rarity of Transitional Varieties||20||
But it may be urged that when several closely-allied species inhabit the same territory, we surely ought to find at the present time many transitional forms.
Let us take a simple case: in travelling from north to south over a continent, we generally meet at successive intervals with closely allied or representative species, evidently filling nearly the same place in the natural economy of the land.
These representative species often meet and interlock; and as the one becomes rarer and rarer, the other becomes more and more frequent, till the one replaces the other.
But if we compare these species where they intermingle, they are generally as absolutely distinct from each other in every detail of structure as are specimens taken from the metropolis inhabited by each.
By my theory these allied species are descended from a common parent; and during the process of modification, each has become adapted to the conditions of life of its own region, and has supplanted and exterminated its original parent-form and all the transitional varieties between its past and present states.
Hence we ought not to expect at the present time to meet with numerous transitional varieties in each region, though they must have existed there, and may be embedded there in a fossil condition.
But in the intermediate region, having intermediate conditions of life, why do we not now find closely-linking intermediate varieties?
This difficulty for a long time quite confounded me.
But I think it can be in large part explained.