undation for the work, helps us but
little in understanding how species arise in nature. How have all those
exquisite adaptations of one part of the organisation to another part,
and to the conditions of life and of one organic being to another being,
been perfected? We see these beautiful co-adaptations most plainly in
the woodpecker and the mistletoe; and only a little less plainly in the
humblest parasite which clings to the hairs of a quadruped or feathers
of a bird; in the structure of the beetle which dives through the water;
in the plumed seed which is wafted by the gentlest breeze; in short, we
see beautiful adaptations everywhere and in every part of the organic
world.

Again, it may be asked, how is it that varieties, which I have called
incipient species, become ultimately converted into good and distinct
species, which in most cases obviously differ from each other far
more than do the varieties of the same species? How do those groups
of species, which constitute what are called distinct genera and which
differ from each other more than do the species of the same genus,
arise? All these results, as we shall more fully see in the next
chapter, follow from the struggle for life. Owing to this struggle,
variations, however slight and from whatever cause proceeding, if they
be in any degree profitable to the individuals of a species, in their
infinitely complex relations to other organic beings and to their
physical conditions of life, will tend to the preservation of such
individuals, and will generally be inherited by the offspring. The
offspring, also, will thus have a better chance of surviving, for, of
the many individuals of any species which are periodically born, but a
small number can survive. I have called this principle, by which
each slight variation, if useful, is preserved, by the term natural
selection, in order to mark its relation to man's power of selection.
But the expression often used by Mr. Herbert Spencer, of the Survival of
the Fittest, is more accurate, and is sometimes equally convenient. We
have seen that man by selection can certainly produce great results, and
can adapt organic beings to his own uses, through the accumulation of
slight but useful variations, given to him by the hand of Nature. But
Natural Selection, we shall hereafter see, is a power incessantly ready
for action, and is as immeasurably superior to man's feeble efforts, as
the works of Nature are to those of Art.