food, and are exposed to the same dangers. In the case of varieties of the same species, the struggle will generally be almost equally severe, and we sometimes see the contest soon decided: for instance, if several varieties of wheat be sown together, and the mixed seed be resown, some of the varieties which best suit the soil or climate, or are naturally the most fertile, will beat the others and so yield more seed, and will consequently in a few years
....... 1872 | quite 1859 1860 1861 1866 1869 |
supplant the other varieties. To keep up a mixed stock of even such extremely close varieties as the
variously-coloured variously-coloured 1872 | variously coloured 1859 1860 1861 1866 1869 |
sweet-peas, they must be each year harvested separately, and the seed then mixed in due
proportion, proportion, 1860 1861 1866 1869 1872 | propor- tion, 1859 |
otherwise the weaker kinds will steadily decrease in
number number 1866 1869 1872 | numbers 1859 1860 1861 |
and disappear. So again with the varieties of
sheep; sheep; 1872 | sheep: 1859 1860 1861 1866 1869 |
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
....... 1869 1872 | one 1859 1860 1861 1866 |
of our domestic plants or animals have so exactly the same strength, habits, and constitution, that the original proportions of a mixed stock
(crossing being prevented) could (crossing being prevented) could 1872 |
could 1859 1860 1861 1866 1869 |
be kept up for
half-a-dozen half-a-dozen 1860 1861 1866 1869 1872 |
half a dozen 1859 |
generations, if they were allowed to struggle together,
in the same manner as in the same manner as 1872 |
like 1859 1860 1861 1866 1869 |
beings in a state of nature, and if the seed or young were not annually
preserved in due proportion. preserved in due proportion. 1872 |
sorted. 1859 1860 1861 1866 1869 |
|
Struggle
Struggle
1866 1872 |
Struggle
1869 |
for
Life
most
severe
severe
1866 1872 |
severe
1869 |
between
between
1866 1872 |
between
1869 |
Individuals
Individuals
1866 1872 |
Individuals
1869 |
and
Varieties
Varieties
1866 1872 |
Varieties
1869 |
of
the
same
Species.
Species.
1872 |
Species.
1866 |
Species. 1869 |
|
As
the species the species 1872 | species 1859 1860 1861 1866 1869 |
of the same genus
usually have, usually have, 1872 | have usually, 1859 1860 1861 1866 1869 |
though by no means invariably,
much much 1866 1869 1872 | some 1859 1860 1861 |
similarity in habits and constitution, and always in structure, the struggle will generally be more severe between
them, if them, if 1872 |
species of the same genus, when 1859 1860 1861 1866 1869 |
they come into competition with each other, than between
the species the species 1872 | species 1859 1860 1861 1866 1869 |
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! In Russia the small Asiatic cockroach has everywhere driven before it its great congener. climates! In Russia the small Asiatic cockroach has everywhere driven before it its great congener. 1869 1872 |
climates! 1859 1860 1861 1866 |
↑1 blocks not present in 1869 1872; present in 1859 1860 1861 1866 | In Russia the small Asiatic cockroach has everywhere driven before it its great congener.
|
In Australia the imported hive-bee is rapidly exterminating the small, stingless native bee. One species of charlock
has been known to has been known to 1866 1869 1872 |
will 1859 1860 1861 |
supplant
another another 1866 1869 1872 | another, 1859 1860 1861 |
species; and species; and 1866 1869 1872 | and 1859 1860 1861 |
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.
|