and so be
preserved. How fleeting are the wishes and efforts of man! How short his
time, and consequently how poor will be his results, compared with those
accumulated by Nature during whole geological periods! Can we wonder
then that Nature's productions should be far "truer" in character than
man's productions; that they should be infinitely better adapted to the
most complex conditions of life, and should plainly bear the stamp of
far higher workmanship?

It may metaphorically be said that Natural Selection is daily and hourly
scrutinizing, throughout the world, the slightest variations; rejecting
those that are bad, preserving and adding up all that are good; silently
and 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 lapse of ages, and then
so imperfect is our view into long-past geological ages, that we see
only that the forms of life are now different from what they formerly
were.

In order that any great amount of modification should be effected in a
species, a variety when once formed must again, perhaps after a long
interval of time, vary or present individual differences of the same
favorable nature as before; and these must be again preserved, and so
onward step by step. Seeing that individual differences of the same kind
perpetually recur, this can hardly be considered as an unwarrantable
assumption. But whether it is true, we can judge only by seeing how far
the hypothesis accords with and explains the general phenomena of
nature. On the other hand, the ordinary belief that the amount of
possible variation is a strictly limited quantity, is likewise a simple
assumption.

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 gray; the Alpine ptarmigan white
in winter, the red grouse the color of heather,--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--