|
We can clearly
this in the case of animals with simple habits. Take the case of a carnivorous quadruped, of which the number that can be supported in any country has long ago arrived at its full average. If its natural
of increase be allowed to act, it can succeed in increasing (the country not undergoing any change in
conditions) only by its varying descendants seizing on places at present occupied by other
some of them, 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. 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
→as
distinct species and genera of
→differ from each other,
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
→thus,
as it may be said,
→is striving its
utmost to increase
|
