d, according to
the principles followed by many palaeontologists, be ranked as new and
distinct species.

If then there be some degree of truth in these remarks, we have no right
to expect to find, in our geological formations, an infinite number of
those fine transitional forms, which, on our theory, have connected
all the past and present species of the same group into one long and
branching chain of life. We ought only to look for a few links, and such
assuredly we do find--some more distantly, some more closely, related
to each other; and these links, let them be ever so close, if found in
different stages of the same formation, would, by many palaeontologists,
be ranked as distinct species. But I do not pretend that I should ever
have suspected how poor was the record in the best preserved geological
sections, had not the absence of innumerable transitional links between
the species which lived at the commencement and close of each formation,
pressed so hardly on my theory.

ON THE SUDDEN APPEARANCE OF WHOLE GROUPS OF ALLIED SPECIES.

The abrupt manner in which whole groups of species suddenly appear in
certain formations, has been urged by several palaeontologists--for
instance, by Agassiz, Pictet, and Sedgwick, as a fatal objection to the
belief in the transmutation of species. If numerous species, belonging
to the same genera or families, have really started into life at once,
the fact would be fatal to the theory of evolution through natural
selection. For the development by this means of a group of forms, all
of which are descended from some one progenitor, must have been an
extremely slow process; and the progenitors must have lived long before
their modified descendants. But we continually overrate the perfection
of the geological record, and falsely infer, because certain genera or
families have not been found beneath a certain stage, that they did not
exist before that stage. In all cases positive palaeontological evidence
may be implicitly trusted; negative evidence is worthless, as experience
has so often shown. We continually forget how large the world is,
compared with the area over which our geological formations have been
carefully examined; we forget that groups of species may elsewhere
have long existed, and have slowly multiplied, before they invaded the
ancient archipelagoes of Europe and the United States. We do not make
due allowance for the enormous intervals of time which have elapsed
betw