take, as an illustration, a perfectly parallel
case. When Kepler was unable to explain by any known causes the paths
described by the planets, he resorted to a supernatural explanation, and
supposed that every planet was guided in its movements by some presiding
angel. But when Newton supplied a beautifully simple physical
explanation, all persons with a scientific habit of mind at once
abandoned the metaphysical one. Now, to be consistent, the
above-mentioned Professors, and all who think with them, ought still to
adhere to Kepler's hypothesis in preference to Newton's explanation;
for, excepting the law of parsimony, there is certainly no other
logical objection to the statement, that the movements of the planets
afford as good evidence of the influence of guiding angels as they do of
the influence of gravitation.

So much, then, for the illogical position that, granting the evidence in
favour of natural descent and supernatural design to be equal and
parallel, we should hesitate in our choice between the two theories.
But, of course, if the evidence is supposed _not_ to be equal and
parallel--i. e. if it is supposed that the theory of natural selection
is not so good a theory whereby to explain the facts of adaptation as is
that of supernatural design,--then the objection is no longer the one
which we are considering. It is quite another objection, and one which
is not _prima facie_ absurd. Therefore let us state clearly the distinct
question which thus arises.

Innumerable cases of adaptation of organisms to their environments are
the observed facts for which an explanation is required. To supply this
explanation, two, and only two, hypotheses are in the field. Of these
two hypotheses one is intelligent design manifested directly in special
creation; the other is natural causation operating through countless
ages of the past. Now, the adaptations in question involve an
innumerable multitude of special mechanisms, in most cases even within
the limits of any one given species; but when we consider the sum of all
these mechanisms presented by organic nature as a whole, the mind must
indeed be dull which does not feel astounded. For, be it further
observed, these mechanical contrivances[36] are, for the most part, no
merely simple arrangements, which might reasonably be supposed due,
like the phenomena of crystallization, to comparatively simple physical
causes. On the contrary, they everywhere and habitually exhibit