her natural species have changed as abruptly
as have occasionally domestic races, and for entirely disbelieving that
they have changed in the wonderful manner indicated by Mr. Mivart, are
as follows. According to our experience, abrupt and strongly marked
variations occur in our domesticated productions, singly and at rather
long intervals of time. If such occurred under nature, they would
be liable, as formerly explained, to be lost by accidental causes of
destruction and by subsequent intercrossing; and so it is known to be
under domestication, unless abrupt variations of this kind are specially
preserved and separated by the care of man. Hence, in order that a new
species should suddenly appear in the manner supposed by Mr. Mivart,
it is almost necessary to believe, in opposition to all analogy, that
several wonderfully changed individuals appeared simultaneously within
the same district. This difficulty, as in the case of unconscious
selection by man, is avoided on the theory of gradual evolution, through
the preservation of a large number of individuals, which varied more
or less in any favourable direction, and of the destruction of a large
number which varied in an opposite manner.

That many species have been evolved in an extremely gradual manner,
there can hardly be a doubt. The species and even the genera of many
large natural families are so closely allied together that it is
difficult to distinguish not a few of them. On every continent, in
proceeding from north to south, from lowland to upland, etc., we meet
with a host of closely related or representative species; as we likewise
do on certain distinct continents, which we have reason to believe were
formerly connected. But in making these and the following remarks, I am
compelled to allude to subjects hereafter to be discussed. Look at
the many outlying islands round a continent, and see how many of their
inhabitants can be raised only to the rank of doubtful species. So it is
if we look to past times, and compare the species which have just passed
away with those still living within the same areas; or if we compare
the fossil species embedded in the sub-stages of the same geological
formation. It is indeed manifest that multitudes of species are related
in the closest manner to other species that still exist, or have lately
existed; and it will hardly be maintained that such species have been
developed in an abrupt or sudden manner. Nor should it be forgo