carnivorous. The more diversified in habits and structure the
descendants of our carnivorous animal became, the more places they
would 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 do 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 thus be raised. The same has been found to hold good
when first one variety and then 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 those varieties were continually selected
which differed from each other in at all the same manner as distinct
species and genera of grasses differ from each other, a greater number
of individual plants of this species of grass, including its modified
descendants, would succeed in living on the same piece of ground. And
we well know that each species and each variety of grass is annually
sowing almost countless seeds; and thus, as it may be said, is striving
its utmost to increase its numbers. Consequently,
I cannot doubt that in the course of many thousands of generations, the
most distinct varieties of any one species of grass would always 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 principle, 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 severe, 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 islets; and so in small ponds of fresh water. Farmers find
that they can raise most food by a rotation of plants belonging to the
most different orders: nature follows what may be called a simultaneous
rotation. Most of the animals and plants which live close round any
small piece of ground, could live on it (supposing it not to be in any
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