to their various species, reveals the lower types whence they issued; in
the successive forms taken by the foetus; in the powerful and
indisputable laws of selection; in the modifications by adaptation of
the different organisms, and in the effects of isolation. This is the
only rational explanation, confirmed as it is by fresh facts every day,
of the multiplicity and variety of organic forms in the lapse of time;
unless, indeed, we ascribe such variety to a miracle, even more
difficult to accept than the difficulties of the opposite-theory.

I admit that evidence for the complete demonstration of this theory is
sometimes wanting; the gaps between the fossil fauna and flora and those
of modern times are neither few nor unimportant; but on the other hand,
such proofs are accumulating, and the gaps are filled up every day, so
that we may almost assert that in some way or other, by means somewhat
different from those on which we now rely, the great rational principle
of evolution will be successfully and permanently established.

It is more than twenty years since, in ways and by study peculiar to
ourselves, we first devoted ourselves to this theory, and while we gave
a conscientious consideration to opposite theories, so as to estimate
with sincerity their importance and value, we could not relinquish our
conviction that every advance in physical, biological, and social
science served to confirm the theory of evolution.

It must not be supposed that I make any dogmatic assertion, which might
possibly be erroneous, when I say that the evidence of facts does not
contradict the assumptions of modern science. Sincere convictions should
offend no one, nor do they indicate an a priori conflict with other
beliefs. Every one is justified in thinking his own thoughts when he
speaks with moderation and supports his peculiar opinions with a certain