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OriginOfSpecies - 475 Rows
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id int(11) 475 Column Stats
subject varchar(80) 14 Column Stats
title varchar(250) 139 Column Stats
ordinal int(11) 30 Column Stats
description text 474 Column Stats

475 rows, page 44 of 119 (4/p)
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04 - Natural Selection 04-14 - Summary of Chapter 20 Whether natural selection has really thus acted in adapting the various forms of life to their several conditions and stations, must be judged by the general tenor and balance of evidence given in the following chapters.

But we have already seen how it entails extinction; and how largely extinction has acted in the world's history, geology plainly declares.

Natural selection also leads to divergence of character; for the more organic beings diverge in structure, habits, and constitution, by so much the more can a large number be supported on the area,- of which we see proof by looking to the inhabitants of any small spot, and to the productions naturalised in foreign lands.

Therefore, during the modification of the descendants of any one species, and during the incessant struggle of all species to increase in numbers, the more diversified the descendants become, the better will be their chance of success in the battle for life.

Thus the small differences distinguishing varieties of the same species, steadily tend to increase, till they equal the greater differences between species of the same genus, or even of distinct genera.
05 - Laws of Variation 05-02 - Use and Disuse of Parts, combined with Natural Selection, Organs of Flight and Vision 20 Kirby has remarked (and I have observed the same fact) that the anterior tarsi, or feet, of many male dung-feeding beetles are often broken off; he examined seventeen specimens in his own collection, and not one had even a relic left.

beetle
beetle


In the Onites apelles, [?], the tarsi are so habitually lost, that the insect has been described as not having them.
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In some other genera they are present, but in a rudimentary condition.

In the Ateuchus, or sacred beetle of the Egyptians, they are totally deficient.

ateuchus
ateuchus


The evidence that accidental mutilations can be inherited is at present not decisive; but the remarkable cases observed by Brown-Sequard in guinea-pigs, of the inherited effects of operations, should make us cautious in denying this tendency.

Guinea
Guinea

Guinea Pig
Guinea Pig


Hence it will perhaps be safest to look at the entire absence of the anterior tarsi in Ateuchus, and their rudimentary condition in some other genera, not as cases of inherited mutilations, but as due to the effects of long-continued disuse; for as many dung-feeding beetles are generally found with their tarsi lost, this must happen early in life; therefore the tarsi cannot be of much importance or be much used by these insects.

ateuchus
ateuchus
05 - Laws of Variation 05-03 - Acclimatisation 20 As we may infer that our domestic animals were originally chosen by uncivilised man because they were useful and because they bred readily under confinement, and not because they were subsequently found capable of far-extended transportation, the common and extraordinary capacity in our domestic animals of not only withstanding the most different climates, but of being perfectly fertile (a far severer test) under them, may be used as an argument that a large proportion of other animals now in a state of nature could easily be brought to bear widely different climates.

We must not, however, push the foregoing argument too far, on account of the probable origin of some of our domestic animals from several wild stocks; the blood, for instance, of a tropical and arctic wolf may perhaps be mingled in our domestic breeds.

wolf
wolf


The rat and mouse cannot be considered as domestic animals, but they have been transported by man to many parts of the world, and now have a far wider range than any other rodent; for they live under the cold climate of Faroe in the north and of the Falklands in the south, and on many an island in the torrid zones.

rat
rat

mouse
mouse

Faroe Islands
Faroe Islands

Falkland Islands
Falkland Islands


Hence adaptation to any special climate may be looked at as a quality readily grafted on an innate wide flexibility of constitution, common to most animals.

On this view, the capacity of enduring the most different climates by man himself and by his domestic animals, and the fact of the extinct elephant and rhinoceros having formerly endured a glacial climate, whereas the living species are now all tropical or sub-tropical in their habits, ought not to be looked at as anomalies, but as examples of a very common flexibility of constitution, brought, under peculiar circumstances, into action.

elephant
elephant

rhinoceros
rhinoceros
05 - Laws of Variation 05-04 - Correlation of Growth 20 Homologous parts, as has been remarked by some authors, tend to cohere; this is often seen in monstrous plants: and nothing is more common than the union of homologous parts in normal structures, as in the union of the petals into a tube.

petal
petal


Hard parts seem to affect the form of adjoining soft parts; it is believed by some authors that with birds the diversity in the shape of the pelvis causes the remarkable diversity in the shape of their kidneys.

bird
bird

pelvis
pelvis

kidney
kidney


Others believe that the shape of the pelvis in the human mother influences by pressure the shape of the head of the child.

In snakes, according to Schlegel, the form of the body and the manner of swallowing determine the position and form of several of the most important viscera.
snake
snake

Hermann Schlegel
Hermann Schlegel