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.
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