F. Then the whole matter lies in a nutshell. Suppose that hundreds of
millions of years ago there existed upon this earth a single primordial
form of the very lowest life, or suppose that three or four such
primordial forms existed. Change of climate, of food, of any of the
circumstances which surrounded any member of this first and lowest class
of life would tend to alter it in some slight manner, and the alteration
would have a tendency to perpetuate itself by inheritance. Many failures
would doubtless occur, but with the lapse of time slight deviations would
undoubtedly become permanent and inheritable, those alone being
perpetuated which were beneficial to individuals in whom they appeared.
Repeat the process with each deviation and we shall again obtain
divergences (in the course of ages) differing more strongly from the
ancestral form, and again those that enable their possessor to struggle
for existence most efficiently will be preserved. Repeat this process
for millions and millions of years, and, as it is impossible to assign
any limit to variability, it would seem as though the present diversities
of species must certainly have come about sooner or later, and that other
divergences will continue to come about to the end of time. The great
agent in this development of life has been competition. This has culled
species after species, and secured that those alone should survive which
were best fitted for the conditions by which they found themselves
surrounded. Endeavour to take a bird’s-eye view of the whole matter.
See battle after battle, first in one part of the world, then in another,
sometimes raging more fiercely and sometimes less; even as in human
affairs war has always existed in some part of the world from the
earliest known periods, and probably always will exist. While a species
is conquering in one part of the world it is being subdued in another,
and while its conquerors are indulging in their triumph down comes the
fiat for their being culled and drafted out, some to life and some to
death, and so forth _ad infinitum_.