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for instance, being enabled to feed on new kinds of prey, either dead or alive; some inhabiting new stations, climbing trees, frequenting water, and some perhaps becoming less carnivorous. The more diversified in habits and structure the descendants of our carnivorous
the more places they
be enabled to occupy. What applies to one animal will apply throughout all time to all animals— that is, if they vary— for otherwise natural selection can
nothing. So it will be with plants. It has been experimentally proved, that if a plot of ground be sown with one species of grass, and a similar plot be sown with several distinct genera of grasses, a greater number of plants and a greater weight of dry herbage can
be
→raised in the latter than in the former case. The same has been found to hold good when
one variety and
several mixed varieties of wheat have been sown on equal spaces of ground. Hence, if any one species of grass were to go on varying, and
varieties were continually selected which differed from each other in
the same
→though in a very slight degree, as do the
distinct species and genera of
→OMIT
a greater number of individual plants of this
including its modified descendants, would succeed in living on the same piece of ground. And we
know that each species and each variety of grass is annually sowing almost countless
and
→is thus striving,
as it may be said,
→to the
utmost to increase
→OMIT
in the course of many
generations, the most distinct varieties of any one species of grass would
have the best chance of succeeding and of increasing in numbers, and thus of supplanting the less distinct varieties; and varieties, when rendered very distinct from each other, take the rank of species. |
| The truth of the
that the greatest amount of life can be supported by great diversification of structure, is seen under many natural circumstances. In an extremely small area, especially if freely open to immigration, and where the contest between individual and individual must be
we always find great diversity in its inhabitants. For instance, I found that a piece of turf, three feet by four in size, which had been exposed for many years to exactly the same conditions, supported twenty species of plants, and these belonged to eighteen genera and to eight orders, which shows how much these plants differed from each other. So it is with the plants and insects on small and uniform
in small ponds of fresh water. Farmers find that they can raise most food by a rotation of plants belonging to the most different
nature follows what may be called a simultaneous rotation. Most of the animals and plants which live close round any small
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