istinct species, is that we are
always slow in admitting any great changes of which we do not see the
steps. The difficulty is the same as that felt by so many geologists,
when Lyell first insisted that long lines of inland cliffs had been
formed, and great valleys excavated, by the agencies which we still see
at work. The mind cannot possibly grasp the full meaning of the term of
even a million years; it cannot add up and perceive the full effects of
many slight variations, accumulated during an almost infinite number of
generations.

Although I am fully convinced of the truth of the views given in this
volume under the form of an abstract, I by no means expect to convince
experienced naturalists whose minds are stocked with a multitude of
facts all viewed, during a long course of years, from a point of view
directly opposite to mine. It is so easy to hide our ignorance under
such expressions as the "plan of creation," "unity of design," etc., and
to think that we give an explanation when we only restate a fact. Any
one whose disposition leads him to attach more weight to unexplained
difficulties than to the explanation of a certain number of facts
will certainly reject the theory. A few naturalists, endowed with
much flexibility of mind, and who have already begun to doubt the
immutability of species, may be influenced by this volume; but I look
with confidence to the future, to young and rising naturalists, who will
be able to view both sides of the question with impartiality. Whoever
is led to believe that species are mutable will do good service by
conscientiously expressing his conviction; for thus only can the load of
prejudice by which this subject is overwhelmed be removed.

Several eminent naturalists have of late published their belief that
a multitude of reputed species in each genus are not real species; but
that other species are real, that is, have been independently created.
This seems to me a strange conclusion to arrive at. They admit that
a multitude of forms, which till lately they themselves thought were
special creations, and which are still thus looked at by the majority of
naturalists, and which consequently have all the external characteristic
features of true species--they admit that these have been produced by
variation, but they refuse to extend the same view to other and slightly
different forms. Nevertheless, they do not pretend that they can define,
or even conjecture, which are the creat