can a variety live side by side with the parent species?
If both have become fitted for slightly different habits of life
or conditions, they might live together; and if we lay on one side
polymorphic species, in which the variability seems to be of a peculiar
nature, and all mere temporary variations, such as size, albinism,
etc., the more permanent varieties are generally found, as 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.

Bronn also insists that distinct species never differ from each other in
single characters, but in many parts; and he asks, how it always comes
that many parts of the organisation should have been modified at the
same time through variation and natural selection? But there is no
necessity for supposing that all the parts of any being have been
simultaneously modified. The most striking modifications, excellently
adapted for some purpose, might, as was formerly remarked, be acquired
by successive variations, if slight, first in one part and then in
another; and as they would be transmitted all together, they would
appear to us as if they had been simultaneously developed. The best
answer, however, to the above objection is afforded by those domestic
races which have been modified, chiefly through man's power of
selection, for some special purpose. Look at the race and dray-horse, or
at the greyhound and mastiff. Their whole frames, and even their mental
characteristics, have been modified; but if we could trace each step
in the history of their transformation--and the latter steps can be
traced--we should not see great and simultaneous changes, but first
one part and then another slightly modified and improved. Even when
selection has been applied by man to some one character alone--of which
our cultivated plants offer the best instances--it will invariably be
found that although this one part, whether it be the flower, fruit, or
leaves, has been greatly changed, almost all the other parts have been
slightly modified. This may be attributed partly to the principle of
correlated growth, and partly to so-called spontaneous variation.

A much more serious objection has been urged by Bronn, and recently by
Broca, namely, that many characters appear to be of no service whatever
to their possessors,