sterile, and varieties invariably fertile; or that sterility is a
special endowment and sign of creation. The belief that species were
immutable productions was almost unavoidable as long as the history of
the world was thought to be of short duration; and now that we have
acquired some idea of the lapse of time, we are too apt to assume,
without proof, that the geological record is so perfect that it would
have afforded us plain evidence of the mutation of species, if they had
undergone mutation.
But the chief cause of our natural unwillingness to admit that one
species has given 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 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, 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 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
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