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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 75 of 119 (4/p)
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Export to Excel select * from OriginOfSpecies order by ordinal desc limit 296, 4 (Page 75: Row)
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05 - Laws of Variation 05-07 - Multiple, Rudimentary, and Lowly-organised Structures are Variable 20 I presume that lowness here means that the several parts of the organisation have been but little specialised for particular functions; and as long as the same part has to perform diversified work, we can perhaps see why it should remain variable, that is, why natural selection should not have preserved or rejected each little deviation of form as carefully as when the part has to serve for some one special purpose.

In the same way, a knife which has to cut all sorts of things may be of almost any shape; whilst a tool for some particular-purpose must be of some particular shape.

knife
knife


Natural selection, it should never be forgotten, can act solely through and for the advantage of each being. Rudimentary parts, as it is generally admitted, are apt to be highly variable.

We shall have to recur to this subject; and I will here only add that their variability seems to result from their uselessness, and consequently from natural selection having had no power to check deviations in their structure.
05 - Laws of Variation 05-09 - Specific Characters more Variable than Generic Characters 20 On the ordinary view of each species having been independently created, why should that part of the structure, which differs from the same part in other independently created species of the same genus, be more variable than those parts which are closely alike in the several species?

I do not see that any explanation can be given.

But on the view that species are only strongly marked and fixed varieties, we might expect often to find them still continuing to vary in those parts of their structure which have varied within a moderately recent period, and which have thus come to differ.

Or to state the case in another manner:- the points in which all the species of a genus resemble each other, and in which they differ from allied genera, are called generic characters; and these characters may be attributed to inheritance from a common progenitor, for it can rarely have happened that natural selection will have modified several distinct species, fitted to more or less widely-different habits, in exactly the same manner: and as these so-called generic characters have been inherited from before the period when the several species first branched off from their common progenitor, and subsequently have not varied or come to differ in any degree, or only in a slight degree, it is not probable that they should vary at the present day.

On the other hand, the points in which species differ from other species of the same genus are called specific characters; and as these specific characters have varied and come to differ since the period when the species branched off from a common progenitor, it is probable that they should still often be in some degree variable,- at least more variable than those parts of the organisation which have for a very long period remained constant.
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.
06 - Difficutiles in Theory 06-04 - Transitions in Habits of Life 20 Here, as on other occasions, I lie under a heavy disadvantage, for, out of the many striking cases which I have collected, I can only give one or two instances of transitional habits and structures in allied species; and of diversified habits, either constant or occasional, in the same species.

And it seems to me that nothing less than a long list of such cases is sufficient to lessen the difficulty in any particular case like that of the bat.
bat
bat