Seite - 423 - in The Origin of Species
Bild der Seite - 423 -
Text der Seite - 423 -
ALTERNATE GLACIAL PERIODS 423
of temperature must have been very slow, and plants un-
doubtedly possess a certain capacity for acclimatisation, as
shown by their transmitting to their offspring different con-
stitutional powers of resisting heat and cold.
In the regular course of events the southern hemisphere
would in its turn be subjected to a severe Glacial period, with
the northern hemisphere rendered warmer; and then the
southern temperate forms would invade the equatorial low-
lands. The northern forms which had before been left on
the mountains would now descend and mingle with the south-
ern forms. These latter, when the warmth returned, would
return to their former homes, leaving some few species on
the mountains, and carrying southward with them some of
the northern temperate forms which had descended from
their mountain fastnesses. Thus, we should have some few
species identically the same in the northern and southern
temperate zones and on the mountains of the intermediate
tropical regions. But the species left during a long time on
these mountains, or in opposite hemispheres, would have to
compete with many new forms and would be exposed to
somewhat different physical conditions; hence they would
be eminently liable to modification, and would generally now
exist as varieties or as representative species; and this is the
case. We must, also, bear in mind the occurrence in both
hemispheres of former Glacial periods; for these will ac-
count, in accordance with the same principles, for the many
quite distinct species inhabiting the same widely separated
areas, and belonging to genera not now found in the inter-
mediate torrid zones.
It is a remarkable fact strongly insisted on by Hooker in
regard to America, and by Alph. de Candolle in regard to
Australia, that many more identical or slightly modified spe-
cies have migrated from the north to the south, than in a
reversed direction. We see, however, a few southern forms
on the mountains of Borneo and Abyssinia. I suspect that
this preponderant migration from the north to the south is
due to the greater extent of land in the north, and to the
northern forms having existed in their own homes in greater
numbers, and having consequently been advanced through
natural selection and competition to a higher stage of per-
zurück zum
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