Page - 163 - in The Origin of Species
Image of the Page - 163 -
Text of the Page - 163 -
STRUCTURES VARIABLE 163
concerns tis is, that those points in our domestic animals,
which at the present time are undergoing rapid change by
continued selection, are also eminently liable to variation.
Look at the individuals of the same breed of the pigeon, and
see what a prodigious amount of difference there is in the
beaks of tumblers, in the beaks and wattle of carriers, in the
carriage and tail of fantails, &c., these being the points now
mainly attended to by English fanciers. Even in the same
sub-breed, as in that of the short-faced tumbler, it is notori-
ously difficult to breed nearly perfect birds, many departing
widely from the standard. There may truly be said to be a
constant struggle going on between, on the one hand, the
tendency to reversion to a less perfect state, as well as an
innate tendency to new variations, and, on the other hand,
the power of steady selection to keep the breed true. In the
long run selection gains the day, and we do not expect to
fail so completely as to breed a bird as coarse as a common
tumbler pigeon from agood short-faced strain. But as long as
selection is rapidly going on, much variability in the parts
undergoing modification may always be expected.
Now let us turn to nature. When a part has been devel-
oped in an extraordinary manner in any one species, com-
pared with the other species of the same genus, we may con-
clude that this part has undergone an extraordinary amount
of modification since the period when the several species
branched off from the common progenitor of the genus. This
period will seldom be remote in any extreme degree, as species
rarely endure for more than one geological period. An extra-
ordinary amount of modification implies an unusually large
and long-continued amount of variability, which has con-
tinually been accumulated by natural selection for the benefit
of the species. But as the variability of the extraordinarily
developed part or organ has been so great and long-continued
within a period not excessively remote, we might, as a gen-
eral rule, still expect to find more variability in such parts
than in other parts of the organisation which have remained
for a much longer period nearly constant. And this, I am
convinced, is the case. That the struggle between natural
selection on the one hand, and the tendency to reversion and
variability on the other hand, will in the course of time
back to the
book The Origin of Species"
The Origin of Species
- Title
- The Origin of Species
- Author
- Charles Darwin
- Publisher
- P. F. Collier & Son
- Location
- New York
- Date
- 1909
- Language
- English
- License
- PD
- Size
- 10.5 x 16.4 cm
- Pages
- 568
- Keywords
- Evolutionstheorie, Evolution, Theory of Evolution, Naturwissenschaft, Natural Sciences
- Categories
- International
- Naturwissenschaften Biologie
Table of contents
- 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