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OriginOfSpecies - 475 Rows
Column Type #Values Column Stats
id int(11) 475 Column Stats
subject varchar(80) 14 Column Stats
title varchar(250) 139 Column Stats
ordinal int(11) 30 Column Stats
description text 474 Column Stats

475 rows, page 62 of 119 (4/p)
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05 - Laws of Variation 05-10 - Secondary Sexual Characters Variable 20 It is a remarkable fact, that the secondary differences between the two sexes of the same species are generally displayed in the very same parts of the organisation in which the species of the same genus differ from each other.

Of this fact I will give in illustration the two first instances which happen to stand on my list; and as the differences inthese cases are of a very unusual nature, the relation can hardly be accidental.

The same number of joints in the tarsi is a character common to very large groups of beetles, but in the Engidoe, as Westwood has remarked, the number vary greatly; and the number likewise differs in the two sexes of the same species.

beetle
beetle


Again in the fossorial hymenoptera, the neuration of the wings is a character of the highest importance, because common to large groups; but in certain genera the neuration differs in the different species, and likewise in the two sexes of the same species.

Sir J. Lubbock has recently remarked, that several minute crustaceans offer excellent illustrations of this law.

"In Pontella, for instance, the sexual characters are afforded mainly by the anterior antennae and by the fifth pair of legs: the specific differences also are principally given by these organs."

crustacean
crustacean

Pontella
Pontella


This relation has a clear meaning on my view: I look at all the species of the same genus as having as certainly descended from a common progenitor, as have the two sexes of any one species.

Consequently, whatever part of the structure of the common progenitor, or of its early descendants, became variable, variations of this part would, it is highly probable, be taken advantage of by natural and sexual selection, in order to fit the several species to their several places in the economy of nature, and likewise to fit the two sexes of the same species to each other, or to fit the males to struggle with other males for the possession of the females.
05 - Laws of Variation 05-10 - Secondary Sexual Characters Variable 30 Finally, then, I conclude that the greater variability of specific characters, or those which distinguish species from species, than of generic characters, or those which are possessed by all the species;- that the frequent extreme variability of an part which is developed in a species in an extraordinary manner in comparison with the same part in its congeners; and the slight degree of variability in a part, however extraordinarily it may be developed, if it be common to a whole group of species;- that the great variability of secondary sexual characters, and their great difference in closely allied species;- that secondary sexual and ordinary specific differences are generally displayed in the same parts of the organisation,- are all principles closely connected together.

All being mainly due to the species of the same group being the descendants of common progenitor, from whom they have inherited much in common,- 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 varied,- to natural selection having more or less completely, according to the lapse of time, overmastered the tendency to reversion and to further variability,- to sexual selection being less rigid than ordinary selection,- 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.
05 - Laws of Variation 05-11 - Species of the Same Genus Vary in an Analogous Manner 10 Distinct Species present analagous Variations, so that a Variety of one Species often assumes a Character proper to an Allied Species, or reverts to some of the Characters of an early Progenitor.- These propositions will be most readily understood by looking to our domestic races.

The most distinct breeds of the pigeon, in countries widely apart, present sub-varieties with reversed feathers on the head, and with feathers on the feet,- characters not possessed by the aboriginal rock-pigeon; these then are analogous variations in two or more distinct races.

Rock Pigeon
Rock Pigeon


The frequent presence of fourteen or even sixteen tail-feathers in the pouter may be considered as a variation representing the normal structure of another race, the fan-tail.

Pouter Pigeon
Pouter Pigeon

Fantail Pigeon
Fantail Pigeon


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 Rutabaga, 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.

turnip
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.
05 - Laws of Variation 05-11 - Species of the Same Genus Vary in an Analogous Manner 20 Many similar cases of analogous variation have been observed by Naudin in the great gourd-family, and by various authors in our cereals.

turgourdnip
turgourdnip

cereals
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.

insect
insect

Benjamin Dann Walsh
Benjamin Dann Walsh


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 loins, a bar at the end of the tail, with the outer feathers externally edged near their basis with white.

As all these marks are characteristic of the parent rock-pigeon, I presume that no one will doubt that this is a case of reversion, and not of a new yet analogous variation appearing in the several breeds.

Rock Pigeon
Rock Pigeon


We may, I think, confidently come to this conclusion, because, as we have seen, these coloured marks are eminently liable to appear in the crossed offspring of two distinct and differently coloured breeds; and in this case there is nothing in the external conditions of life to cause the reappearance of the slaty-blue, with the several marks, beyond the influence of the mere act of crossing on the laws of inheritance.