Origin of Species Variorum

→ 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

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

supplant the other varieties. To keep up a mixed stock of even such extremely close varieties as the

variously-coloured

variously coloured

sweet-peas, they must be each year harvested separately, and the seed then mixed in due

propor- tion,

proportion,

otherwise the weaker kinds will steadily decrease in

number

numbers

and disappear. So again with the varieties of

sheep;

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

~~one~~

one

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. →

the species

species

of the same genus

usually have,

have usually,

though by no means invariably,

much

some

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

the species

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