Seite - 127 - in The Origin of Species
Bild der Seite - 127 -
Text der Seite - 127 -
EFFECTS OF NATURAL SELECTIOx^ 127
small genera; and the varying species of the large genera
present a greater number of varieties. We have, also, seen
that the species, which are the commonest and the most
widely diffused, vary more than do the rare and restricted
species. Let (A) be a common, widely-diffused, and varying
species, belonging to a genus large in its own country. The
branching and diverging dotted lines of unequal lengths pro-
ceeding from (A), may represent its varying offspring. The
variations are supposed to be extremely slight, but of the
most diversified nature; they are not supposed all to appear
simultaneously, but often after long intervals of time
; nor
are they all supposed to endure for equal periods. Only those
variations which are in some way profitable will be preserved
or naturally selected. And here the importance of the prin-
ciple of benefit derived from divergence of character comes
in
; for this will generally lead to the most different or di-
vergent variations (represented by the outer dotted lines)
being preserved and accumulated by natural selection. When
a dotted line reaches one of the horizontal lines, and is there
marked by a small numbered letter, a sufficient amount of
variation is supposed to have been accumulated to form it
into a fairly well-marked variety, such as would be thought
worthy of record in a systematic work.
The intervals between the horizontal lines in the diagram,
may represent each a thousand or more generations. After a
thousand generations, species (A) is supposed to have pro-
duced two fairly well-marked varieties, namely a* and w\
These two varieties will generally still be exposed to the
same conditions which made their parents variable, and the
tendency to variability is in itself hereditary ; consequently
they will likewise tend to vary, and commonly in nearly the
same manner as did their parents. Moreover, these two
varieties, being only slightly modified forms, will tend to
inherit those advantages which made their parent (A) more
numerous than most of the other inhabitants of the same
country; they will also partake of those more general advan-
tages which made the genus to which the parent-species
belonged, a large genus in its own country. And all
these circumstances are favorable to the production of new
varieties.
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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