Seite - 233 - in The Origin of Species
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Text der Seite - 233 -
THEORY OF NATURAL SELECTION 233
more favourable than others for the development of so large
a quadruped as the giraffe.
In order that an animal should acquire some structure
specially and largely developed, it is almost indispensable
that several other parts should be modified and co-adapted.
Although every part of the body varies slightly, it does not
follow that the necessary parts should always vary in the
right direction and to the right degree. With the different
species of our domesticated animals we know that the parts
vary in a different manner and degree; and that some species
are much more variable than others. Even if the fitting vari-
ations did arise, it does not follow that natural selection
would be able to act on them, and produce a structure which
apparently would be beneficial to the species. For instance,
if the number of individuals existing in a country is deter-
mined chiefly through destruction by beasts of prey,—by ex-
ternal or internal parasites, etc., —as seems often to be the
case, then natural selection will be able to do little, or will be
greatly retarded, in modifying any particular structure for ob-
taining food. Lastly, natural selection is a slow process, and
the same favourable conditions must long endure in order
that any marked effect should thus be produced. Except by
assigning such general and vague reasons, we cannot explain
why, in many quarters of the world, hoofed quadrupeds have
not acquired much elongated necks or other means for brows-
ing on the higher branches of trees.
Objections of the same nature as the foregoing have been
advanced by many writers. In each case various causes, be-
sides the general ones just indicated, have probably inter-
fered with the acquisition through natural selection of struc-
tures, which it is thought would be beneficial to certain
species. One writer asks, why has not the ostrich acquired
the power of flight? But a moment's reflection will show
what an enormous supply of food would be necessary to give
to this bird of the desert force to move its huge body through
the air. Oceanic islands are inhabited by bats and seals, but
by no terrestrial mammals ; yet as some of these bats are
peculiar species, they must have long inhabited their present
homes. Therefore Sir C. Lyell asks, and assigns certain rea-
sons in answer, why have not seals and bats given birth on
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Buch The Origin of Species"
The Origin of Species
- Titel
- The Origin of Species
- Autor
- Charles Darwin
- Verlag
- P. F. Collier & Son
- Ort
- New York
- Datum
- 1909
- Sprache
- englisch
- Lizenz
- PD
- Abmessungen
- 10.5 x 16.4 cm
- Seiten
- 568
- Schlagwörter
- Evolutionstheorie, Evolution, Theory of Evolution, Naturwissenschaft, Natural Sciences
- Kategorien
- International
- Naturwissenschaften Biologie
Inhaltsverzeichnis
- EDITOR'S INTRODUCTION 5
- AN HISTORICAL SKETCH of the Progress of Opinion on the Origin of Species 9
- INTRODUCTION 21
- Variation under Domestication 25
- Variation under Nature 58
- Struggle for Existence 76
- Natural Selection; or the Survival of the Fittest 93
- Laws of Variation 145
- Difficulties of the Theory 178
- Miscellaneous Objections to the Theory of Natural Selection 219
- Instinct 262
- Hybridism 298
- On the Imperfection of the Geological Record 333
- On the Geological Succession of Organic Beinss 364
- Geographical Distribution 395
- Geographical Distribution - continued 427
- Mutual Affinities of Organic Beings: Morphology: Embryology: Rudimentary Organs 450
- Recapitulation and Conclusion 499
- GLOSSARY 531
- INDEX 541