insensibly working, whenever and wherever opportunity offers, at
the improvement of each organic being in relation to its organic and
inorganic conditions of life. We see nothing of these slow changes in
progress, until the hand of time has marked the long lapse of ages, and
then so imperfect is our view into long past geological ages, that
we only see that the forms of life are now different from what they
formerly were.

Although natural selection can act only through and for the good of each
being, yet characters and structures, which we are apt to consider as of
very trifling importance, may thus be acted on. When we see leaf-eating
insects green, and bark-feeders mottled-grey; the alpine ptarmigan white
in winter, the red-grouse the colour of heather, and the black-grouse
that of peaty earth, we must believe that these tints are of service to
these birds and insects in preserving them from danger. Grouse, if not
destroyed at some period of their lives, would increase in countless
numbers; they are known to suffer largely from birds of prey; and hawks
are guided by eyesight to their prey,--so much so, that on parts of the
Continent persons are warned not to keep white pigeons, as being the
most liable to destruction. Hence I can see no reason to doubt that
natural selection might be most effective in giving the proper colour
to each kind of grouse, and in keeping that colour, when once acquired,
true and constant. Nor ought we to think that the occasional destruction
of an animal of any particular colour would produce little effect: we
should remember how essential it is in a flock of white sheep to destroy
every lamb with the faintest trace of black. In plants the down on
the fruit and the colour of the flesh are considered by botanists
as characters of the most trifling importance: yet we hear from
an excellent horticulturist, Downing, that in the United States
smooth-skinned fruits suffer far more from a beetle, a curculio, than
those with down; that purple plums suffer far more from a certain
disease than yellow plums; whereas another disease attacks
yellow-fleshed peaches far more than those with other coloured flesh.
If, with all the aids of art, these slight differences make a great
difference in cultivating the several varieties, assuredly, in a state
of nature, where the trees would have to struggle with other trees and
with a host of enemies, such differences would effectually settle which
variety, whether