would be no necessity for such an arrangement on the
hypothesis of fixity of species ; but it is just what we
should expect to find on the hypothesis of the transmu
tation of species. Now, in this connection we venture to
assert that there is no trace of the action of Natural
Selection, but that, on the contrary, the principles of
Natural Selection present great difficulties when we
associate them with geographical distribution and the
consequent transmutation of species.
The cause of emigration is to be found in increase of
numbers. Mr. Wallace says :—
“Animals multiply so rapidly that we may consider them as con
tinually trying to extend their range.”—(Geographical Distribution
of Animals and Plants, vol. p. y.)
But this assumption, that animals will always be trying
to extend their range and that they will be forced to do
so by continually increasing numbers, which make a given
area a congested district so far as that species is con
cerned, is not in accordance with the fact that, under
ordinary occasions, the population of any species over a
given area is uniform from generation to generation
because the destruction is equal to the output of life.
Nor does it seem to be generally true that animals
manifest a universal readiness to migrate and to settle
elsewhere.
“The more permanent varieties are generally found, so far as
I can discover, inhabiting distinct stations, such as high land or low
land, dry or moist districts. Moreover in the case of animals which
wander much about and cross freely, their varieties seem to be
generally confined to distinct regions.”—(Origin of Species, p. i6ç.)
“ Most animals and plants keep to their proper homes and do not
needlessly wander about. We see this even with migratory birds,
which almost always return to the same spot.”—(Origin of Species.
A 72-)