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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 unknown influences. In the vegetable kingdom we have a case of analogous variation, in the enlarged stems, or
→as commonly called roots,
of the Swedish turnip and Ruta baga, plants which several botanists rank as varieties produced by cultivation from a common parent: if this be not so, the case will then be one of analogous variation in two so-called distinct species; and to these a third may be added, namely, the common turnip. According to the ordinary view of each species having been independently created, we should have to attribute this similarity in the enlarged stems of these three plants, not to the
vera
causa
of community of descent, and a consequent tendency to vary in a like manner, but to three separate yet closely related acts of creation. Many similar cases of analogous variation have been observed by Naudin in the great gourd-family, and by various authors in our cereals. Similar cases occurring with insects under
natural conditions have lately been discussed with much ability by Mr. Walsh, who has grouped them under his law of Equable Variability. |
| With pigeons, however, we have another case, namely, the occasional appearance in all the breeds, of slaty-blue birds with two black bars on the wings,
white
a bar at the end of the tail, with the outer feathers externally edged near their bases with white. As all these marks are characteristic of the parent
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