se to have been at work. The
radical distinction between the two theories consists in the one
assuming an immediate action of some supernatural or inscrutable cause,
while the other assumes the immediate action of natural--and therefore
of possibly discoverable--causes. But in order to sustain this latter
assumption, the theory of descent is under no logical necessity to
furnish a full proof of _all_ the natural causes which may have been
concerned in working out the observed results. We do not know the
natural causes of many diseases; but yet no one nowadays thinks of
reverting to any hypothesis of a supernatural cause, in order to explain
the occurrence of any disease the natural causation of which is obscure.
The science of medicine being in so many cases able to explain the
occurrence of disease by its hypothesis of natural causes, medical men
now feel that they are entitled to assume, on the basis of a wide
analogy, and therefore on the basis of a strong antecedent presumption,
that all diseases are due to natural causes, whether or not in
particular cases such causes happen to have been discovered. And from
this position it follows that medical men are not logically bound to
entertain any supernatural theory of an obscure disease, merely because
as yet they have failed to find a natural theory. And so it is with
biologists and their theory of descent. Even if it be fully proved to
them that the causes which they have hitherto discovered, or suggested,
are inadequate to account for all the facts of organic nature, this
would in no wise logically compel them to vacate their theory of
evolution, in favour of the theory of creation. All that it would so
compel them to do would be to search with yet greater diligence for the
natural causes still undiscovered, but in the existence of which they
are, by their independent evidence in favour of the theory, bound to
believe.

In short, the issue is not between the theory of a supernatural cause
and the theory of any one particular natural cause, or set of
causes--such as natural selection, use, disuse, and so forth. The issue
thus far--or where only the _fact_ of evolution is concerned--is between
the theory of a supernatural cause as operating immediately in
numberless acts of special creation, and the theory of natural causes as
a whole, whether these happen, or do not happen, to have been hitherto
discovered.

This much by way of preliminaries being understood, we have