Comparison with 1869 |
|
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 quite
supplant the other varieties. To keep up a mixed stock of even such extremely close varieties as the variously coloured
sweet-peas, they must be each year harvested separately, and the seed then mixed in due propor- tion,
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:
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 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.
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Struggle
for
Life
most
severe
between
Individuals
and
Varieties
of
the
same
Species.
|
As species
of the same genus have usually,
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 species of the same genus, when
they come into competition with each other, than between 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. 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
|
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
quite quite 1859 1860 1861 1866 1869 | quite 1872 |
supplant the other varieties. To keep up a mixed stock of even such extremely close varieties as the
variously coloured variously coloured 1859 1860 1861 1866 1869 | variously-coloured 1872 |
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
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 1860 1861 1866 1869 1872 |
half a dozen 1859 |
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
|