otherwise the weaker kinds will steadily decrease in
numbers numbers 1859 1860 1861 | number 1866 1869 1872 |
and disappear. So again with the varieties of
sheep: sheep: 1859 1860 1861 1866 1869 | sheep; 1872 |
it has been asserted that certain mountain-varieties will starve out other mountain-varieties, so that they cannot be kept together. The same result has followed from keeping together different varieties of the medicinal leech. It may even be doubted whether the varieties of any
one one 1859 1860 1861 1866 | one 1869 1872 |
of our domestic plants or animals have so exactly the same strength, habits, and constitution, that the original proportions of a mixed stock
could could 1859 1860 1861 1866 1869 |
(crossing being prevented) could 1872 |
be kept up for
half a dozen half a dozen 1859 |
half-a-dozen 1860 1861 1866 1869 1872 |
generations, if they were allowed to struggle together,
like like 1859 1860 1861 1866 1869 |
in the same manner as 1872 |
beings in a state of nature, and if the seed or young were not annually
sorted. sorted. 1859 1860 1861 1866 1869 |
preserved in due proportion. 1872 |
↑Subtitle not present 1859 1860 1861 |
Struggle
for
Life
most
severe
between
Individuals
and
Varieties
of
the
same
Species.
1866 1869 1872 |
|
As
species species 1859 1860 1861 1866 1869 | the species 1872 |
of the same genus
have usually, have usually, 1859 1860 1861 1866 1869 | usually have, 1872 |
though by no means invariably,
some some 1859 1860 1861 | much 1866 1869 1872 |
similarity in habits and constitution, and always in structure, the struggle will generally be more severe between
species of the same genus, when species of the same genus, when 1859 1860 1861 1866 1869 |
them, if 1872 |
they come into competition with each other, than between
species species 1859 1860 1861 1866 1869 | the species 1872 |
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. The recent increase of the missel-thrush in parts of Scotland has caused the decrease of the song-thrush. How frequently we hear of one species of rat taking the place of another species under the most different
climates! climates! 1859 1860 1861 1866 |
climates! In Russia the small Asiatic cockroach has everywhere driven before it its great congener. 1869 1872 |
In Russia the small Asiatic cockroach has everywhere driven before it its great congener. ↑1 blocks not present in 1859 1860 1861; present in 1866 1869 1872 | In Australia the imported hive-bee is rapidly exterminating the small, stingless native bee.
|
One species of charlock
will will 1859 1860 1861 |
has been known to 1866 1869 1872 |
supplant
another, another, 1859 1860 1861 | another 1866 1869 1872 |
and and 1859 1860 1861 | species; and 1866 1869 1872 |
so in other cases. 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.
|