M Database Inspector (cheetah)
Not logged in. Login

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 52 of 119 (4/p)
1 10 20 30 40 46 47 48 49 50 51 52 53 54 55 56 57 58 60 70 80 90 100 110 119

Export to Excel select * from OriginOfSpecies order by subject, title, ordinal limit 204, 4 (Page 52: Row)
subject
title
ordinal
description
04 - Natural Selection 04-13 - Convergence of Character 50 Consequently there seems at first sight no limit to the amount of profitable diversification of structure, and therefore no limit to the number of species which might be produced.

We do not know that even the most prolific area is fully stocked with specific forms: at the Cape of Good Hope and in Australia, which support such an astonishing number of species, many European plants have become naturalised.

Cape of Good Hope
Cape of Good Hope

Australia
Australia

europe
europe


But geology shows us, that from an early part of the tertiary period the number of species of shells, and that from the middle part of this same period the number of mammals, has not greatly or at all increased.

Sea Shell
Sea Shell
04 - Natural Selection 04-13 - Convergence of Character 60 What then checks an indefinite increase in the number of species?

The amount of life (I do not mean the number of specific forms) supported on an area must have a limit, depending so largely as it does on physical conditions; therefore, if an area be inhabited by very many species, each or nearly each species will be represented by few individuals; and such species will be liable to extermination from accidental fluctuations in the nature of the seasons or in the number of their enemies.
04 - Natural Selection 04-13 - Convergence of Character 70 The process of extermination in such cases would be rapid, whereas the production of new species must always be slow.

Imagine the extreme case of as many species as individuals in England, and the first severe winter or very dry summer would exterminate thousands on thousands of species.

England
England


Rare species, and each species will become rare if the number of species in any country becomes indefinitely increased, will, on the principle often explained, present within a given period few favourable variations; consequently, the process of giving birth to new specific forms would thus be retarded.
04 - Natural Selection 04-13 - Convergence of Character 80 When any species becomes very rare, close interbreeding will help to exterminate it; authors have thought that this comes into play in accounting for the deterioration of the aurochs in Lithuania, of red deer in Scotland, and of bears in Norway, &e. Lastly, and this I am inclined to think is the most important element, a dominant species, which has already beaten many competitors in its own home, will tend to spread and supplant many others.

auroch
auroch

Lithuania
Lithuania

Red Deer
Red Deer

Scotland
Scotland

bear
bear

Norway
Norway


Alph. de Candolle has shown that those species which spread widely, tend generally to spread very widely; consequently, they will tend to supplant and exterminate several species in several areas, and thus cheek the inordinate increase of specific forms throughout the world.

Dr. Hooker has recently shown that in the S.E. corner of Australia, where, apparently, there are many invaders from different quarters of the globe, the endemic Australian species have been greatly reduced in number.

How much weight to attribute to these several considerations I will not pretend to say; but conjointly they must limit in each country the tendency to an indefinite augmentation of specific forms.