ally be local or confined
to one place, but if possessed {302} of any decided advantage, or when
further modified and improved, they would slowly spread and supplant their
parent-forms. When such varieties returned to their ancient homes, as they
would differ from their former state, in a nearly uniform, though perhaps
extremely slight degree, they would, 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 my theory assuredly 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, some more closely,
some more distantly related to each other; and these links, let them be
ever so close, if found in different stages of the same formation, would,
by most palaeontologists, be ranked as distinct species. But I do not
pretend that I should ever have suspected how poor a record of the
mutations of life, the best preserved geological section presented, had not
the difficulty of our not discovering innumerable transitional links
between the species which appeared 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 by none more forcibly than by Professor 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 {303}
started into life all at once, the fact would be fatal to the theory of
descent with slow modification through natural selection. For the
development of a group of forms, all of which have descended from some one
progenitor, must have been an extremely slow process; and the progenitors
must have lived long ages before their modified descendants. But we
continually over-rate 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. We continually
forget how large the world is, compared with the area over which our
geol