h explains the law of _the survival of the
fittest_.

It is a well-known fact that man can, by pursuing a certain method of
breeding or cultivation, improve and in various ways modify the
character of the different domestic animals and plants. By always
selecting the best specimen from which to propagate the race, those
features which it is desired to perpetuate become more and more
developed; so that what are admitted to be real varieties sometimes
acquire, in the course of successive generations, a character as
strikingly distinct, to all appearances, from those of the varieties, as
one species is from another species of the same genus. It is evident
that both natural and artificial selection depends on adaptation and
inheritance. The difference between the two forms of selection is that,
in the first case, the will of man makes the selection according to a
plan, whereas in natural selection the struggle for life and the
survival of the fittest acts without a plan other than that the most
adaptable organism shall survive which is most fit to contend with the
circumstances under which it is placed. Natural selection acts,
therefore, much more slowly than artificial selection, although it
brings about the same end. Adaptation in the struggle for life is an
absolute necessity.

In every act of breeding, a certain amount of protoplasm is transferred
from the parents to the child, and along with it there is transferred
the individual peculiar molecular motion. Adaptation or transmutation
depends upon the material influence which organism experiences from its
surroundings, or its conditions of existence; while the transmission
from inheritance is due to the partial identity of producing and
produced organisms.

Organized beings, as a rule, are gifted with enormous powers of
increase. Wild plants yield their crop of seed annually, and most wild
animals bring forth their young yearly or oftener. Should this process
go on unchecked, in a short time the earth would be completely overrun
with living beings. It has been calculated that if a plant produces
fifty seeds (which is far below the reproductive capacity of many
plants) the first year, each of these seeds growing up into a plant
which produces fifty seeds, or altogether two thousand five hundred
seeds the next year, and so on, it would under favorable conditions of
growth give rise in nine years to more plants by five hundred trillions
than there are square feet of dr