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Export to Excel select * from OriginOfSpecies where title = '03-10 - Struggle for Life most severe between Individuals and Varieties of the same Species' order by subject, title, ordinal ( Row)
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03 - Struggle for Existence 03-10 - Struggle for Life most severe between Individuals and Varieties of the same Species 10 As the species of the same genus usually have, though by no means invariably, much similarity in habits and constitution, and always in structure, the struggle will generally be more severe between them, if they come into competition with each other, than between the species of distinct genera.

We see this in the recent extension over parts of the United States of one species of swallow having caused the decrease of another species.

United States
United States

swallow
swallow


The recent increase of the missel-thrush in parts of Scotland has caused the decrease of the song-thrush.

Scotland
Scotland

Missel Thrush
Missel Thrush

Song Thrush
Song Thrush
03 - Struggle for Existence 03-10 - Struggle for Life most severe between Individuals and Varieties of the same Species 20 How frequently we hear of one species of rat taking the place of another species under the most different climates!

In Russia the small Asiatic cockroach has everywhere driven before it its great congener.

rat
rat

Russia
Russia

cockroach
cockroach


In Australia the imported hive-bee is rapidly exterminating the small, stingless native bee. One species of charlock has been known to supplant another species; and so in other cases.

Australia
Australia

Hive Bee
Hive Bee

charlock
charlock


We can dimly see why the competition should be most severe between allied forms, which fill nearly the same place in the economy of nature; but probably in no one case could we precisely say why one species has been victorious over another in the great battle of life.