All advances by degrees in Nature, and nothing by leaps, and this
law as applied to each, is part of my doctrine of Continuity. Although
there may exist in some other world species intermediate between Man
and the Apes, Nature has thought it best to remove them from us, in
order to establish our superiority beyond question. I speak of intermediate
species, and by no means limit myself to those leading to Man. I
strongly approve of the research for analogies; plants, insects, and
Comparative Anatomy will increase these analogies, especially when
we are able to take advantage of the microscope more than at present.
-- Gottfried Wilhelm Leibniz, Protogaea, 1749
Related:
The agreement of so many kinds of animals in a certain common structure
which seems to be fundamental not only in their skeletons, but also
in the arrangement of the other parts - so that a wonderfully simple
typical form, by the shortening and lengthening of some parts, and
by the suppression and development of others, might be able to produce
an immense variety of species - allows a ray of hope, however faint,
to enter our minds, that here perhaps some result may be obtained,
by the application of the principle of the mechanism of nature (without
which there can be no natural science in general)....