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and ordinary specific differences are generally displayed in the same parts of the
are all principles closely connected together. All being mainly due to the species of the same group
→having descended from
a common progenitor, from whom they have inherited much in
to parts which have recently and largely varied being more likely still to go on varying than parts which have long been inherited and have not
to natural selection having more or less completely, according to the lapse of time, overmastered the tendency to reversion and to further
to sexual selection being less rigid than ordinary
and to variations in the same parts having been accumulated by natural and sexual selection, and
→having been thus
adapted for secondary sexual, and for ordinary
purposes. |
| These propositions will be most readily understood by looking to our domestic races. The most distinct breeds of
in countries
widely apart, present sub-varieties with reversed feathers on the
and
on the
characters not possessed by the aboriginal rock-pigeon; these then are analogous variations in two or more distinct races. The frequent presence of fourteen or even sixteen tail-feathers in the
may be considered as a variation representing the normal structure of another race, the fantail. I presume that no one will doubt that all such analogous variations are due to the several races of the pigeon having inherited from a common parent the same constitution and tendency to variation, when acted on by similar
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