en birth to other and distinct species, is that we are always slow
in admitting any great change of which we do not see the intermediate
steps. The difficulty is the same as that felt by so many geologists, when
Lyell first insisted that long {482} lines of inland cliffs had been
formed, and great valleys excavated, by the slow action of the coast-waves.
The mind cannot possibly grasp the full meaning of the term of a hundred
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," &c., 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
my theory. A few naturalists, endowed with much flexibility of mind, and
who have already begun to doubt on 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 only thus 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 {483} they themselves thought were special
creations, and which are still thus looked at by the majority of
naturalists, and which consequently have every external characteristic
feature of true species,--they admit that these have been produced by
variation, but they refuse to extend the same view to other and very
slightly different forms. Nevertheless they do not pretend that they can