→ could 1859 1860 1861 1866 1869 |
(crossing being prevented) could 1872 |
|
→ half-a-dozen 1860 1861 1866 1869 1872 |
half a dozen 1859 |
|
→ like 1859 1860 1861 1866 1869 |
in the same manner as 1872 |
|
→ 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 |
→ species of the same genus, when 1859 1860 1861 1866 1869 |
them, if 1872 |
|
→ climates! 1859 1860 1861 1866 |
climates! In Russia the small Asiatic cockroach has everywhere driven before it its great congener. 1869 1872 |
|
↑ 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.
|
|
→ will 1859 1860 1861 |
has been known to 1866 1869 1872 |
|
sweet-peas, they must be each year harvested separately, and the seed then mixed in due
otherwise the weaker kinds will steadily decrease in
and disappear. So again with the varieties of
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
of our domestic plants or animals have so exactly the same strength, habits, and constitution, that the original proportions of a mixed stock
→could
be kept up for
→half-a-dozen
generations, if they were allowed to struggle together,
→like
beings in a state of nature, and if the seed or young were not annually
→sorted.
→
|
As
of the same genus
though by no means invariably,
similarity in habits and constitution, and always in structure, the struggle will generally be more severe between
→species of the same genus, when
they come into competition with each other, than between
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. ↑
One species of charlock
→will
supplant
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;
|