Seite - 166 - in The Origin of Species
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Text der Seite - 166 -
166 ORIGIN OF SPECIES
since the period when the species branched off from a com-
mon progenitor, it is probable that they should still often be
in some degree variable,—at least more variable than those
parts of the organisation which have for a very long period
remained constant.
Secondary Sexual Characters Variable.—I think it will be
admitted by naturalists, without my entering on details, that
secondary sexual characters are highly variable. It will also
be admitted that species of the same group differ from each
other more widely in their secondary sexual characters, than
in other parts of their organisation: compare, for instance,
the amount of difference between the males of gallinaceous
birds, in which secondary sexual characters are strongly dis-
played, with the amount of difference between the females.
The cause of the original variability of these characters is
not manifest; but we can see why they should not have been
rendered as constant and uniform as others, for they are
accumulated by sexual selection, which is less rigid in its ac-
tion than ordinary selection, as it does not entail death, but
only gives fewer offspring to the less favoured males. What-
ever the cause may be of the variability of secondary sexual
characters, as they are highly variable, sexual selection will
have had a wide scope for action, and may thus have suc-
ceeded in giving to the species of the same group a greater
amount of difference in these than in other respects.
It is a remarkable fact, that the secondary differences be-
tween the two sexes of the same species are generally dis-
played in the very same parts of the organisation in which
the species of the same genus differ from each other. Of
this fact I will give in illustration the two first instances
which happen to stand on my list; and as the differences in
these cases are of a very unusual nature, the relation can
hardly be accidental. The same number of joints in the tarsi
is a character common to very large groups of beetles, but
in the Engidas, as Westwood has remarked, the number varies
greatly; and the number likewise differs in the two sexes of
the same species. Again in the fossorial hymenoptera, the
neuration of the wings is a character of the highest impor-
tance, because common to large groups ; but in certain genera
the neuration differs in the different species, and likewise in
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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