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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 40 of 119 (4/p)
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Export to Excel select * from OriginOfSpecies order by ordinal limit 156, 4 (Page 40: Row)
subject
title
ordinal Desending Order (top row is first)
description
04 - Natural Selection 04-01 - Natural Selection 20 Variations neither useful nor injurious would not be affected by natural selection, and would be left either a fluctuating element, as perhaps we see in certain polymorphic species, or would ultimately become fixed, owing to the nature of the organism and the nature of the conditions.
03 - Struggle for Existence 03-05 - Nature of the Checks to Increase 20 The causes which check the natural tendency of each species to increase are most obscure.

Look at the most vigorous species; by as much as it swarms in numbers, by so much will it tend to increase still further.

We know not exactly what the checks are even in a single
instance.

Nor will this surprise any one who reflects how ignorant we are on this head, even in regard to mankind, although so incomparably better known than any other animal.

This subject of the checks to increase has been ably treated by several authors, and I hope in a future work to discuss it at considerable length, more especially in regard to the feral animals of South America.

Mustang (Feral Horse)
Mustang (Feral Horse)

Feral Cat (re-homed)
Feral Cat (re-homed)


Here I will make only a few remarks, just to recall to the reader's mind some of the chief points.
04 - Natural Selection 04-08 - On the Intercrossing of Individuals 20 In the first place, I have collected so large a body of facts, and made so many experiments, showing, in accordance with the almost universal belief of breeders, that with animals and plants a cross between different varieties, or between individuals of the same variety but of another strain, gives vigour and fertility to the offspring; and on the other hand, that close interbreeding diminishes vigour and fertility; that these facts alone incline me to believe that it is a general law of
nature that no organic being fertilises itself for a perpetuity of generations; but that a cross with another individual is occasionally- perhaps at long intervals of time- indispensable.
05 - Laws of Variation 05-12 - Reversion to Long Lost Characters 20 As all the species of the same genus are supposed to be descended from a common progenitor, it might be expected that they would occasionally vary in an analogous manner; so that the varieties of two or more species would resemble each other, or that a variety of one species would resemble in certain characters another and distinct species,- this other species being, according to our view, only a well marked and permanent variety.

But characters exclusively due to analogous variation would probably be of an unimportant nature, for the preservation of all functionally important characters will have been determined through natural selection, in accordance with the different habits of the species.

It might further be expected that the species of the same genus would occasionally exhibit reversions to long lost characters.

As, however, we do not know the common ancestors of any natural group, we cannot distinguish between reversionary and analogous characters.

If, for instance, we did not know that the parent rock-pigeon was not feather-footed or turn-crowned, we could not have told, whether such characters in our domestic breeds were reversions or only analogous variations; but we might have inferred that the blue colour was a case of reversion from the number of the markings, which are correlated with this tint, and which would not probably have all appeared together from simple variation.

Rock Pigeon
Rock Pigeon


More especially we might have inferred this, from the blue colour and the several marks so often appearing when differently coloured breeds are crossed.

Hence, although under nature it must generally be left doubtful, what cases are reversions to formerly existing characters, and what are new but analogous variations, yet we ought, on our theory, sometimes to find the varying offspring of a species assuming characters which are already present in other members of the same group.

And this undoubtedly is the case. The difficulty in distinguishing variable species is largely due to the varieties mocking, as it were, other species of the same genus.