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, and therefore cannot have been influenced through natural
selection. Bronn adduces the length of the ears and tails in the different
species of hares and mice--the complex folds of enamel in the teeth of many
animals, and a multitude of analogous cases. With respect to plants, this
subject has been discussed by Nageli in an admirable essay. He admits that
natural selection has effected much, but he insists that the families of
plants differ chiefly from each other in morphological characters, which
appear to be quite unimportant for the welfare of the species. He
consequently believes in an innate tendency towards progressive and more