| Of the objections, some seem to me unimportant, some few are owing to misapprehension, and some are incidentally noticed in various parts of this volume.
On the erroneous supposition that all the species of a region are believed by me to be changing at the same time, he justly asks how it is that all the forms of life do not present a fluctuating and inextricably confused body?
but it is sufficient for us if some few forms at any one time are variable, and few will dispute that this is the case.
He asks, how
can it be
on the principle of natural selection
that
a variety should
live in abundance side by side with the parent species;
for the
variety during its formation is supposed to have
supplanted
the intermediate forms between itself and the parent species,
and yet it has not supplanted the parent species itself,
for both are supposed now to live side by side?
If the variety and parent species
have become fitted to
slightly different habits of life, they might live together; though
in the case of animals which freely cross and move about, varieties seem to be almost always confined to distinct localities.
But is it the case that varieties of plants and of the lower animals are often found in abundance side by side with the parent forms?
Laying aside the
polymorphic species
in which the
innumerable variations that occur
seem neither advantageous nor disadvantageous to the species, and have not been fixed; laying aside also temporary variations, such as albinism, &c., my impression is that varieties and the supposed parent species
are generally found,
inhabiting either
distinct stations, high land or low land, dry or moist districts, or distinct regions.
Again, Professor Bronn truly remarks, that distinct species do not differ from each other in single characters alone, but in many; and he asks, how it comes that natural selection should always have simultaneously affected many parts of the organisation?
Probably the whole amount of difference has not been simultaneously effected; and the unknown laws of correlation will certainly account for, but not strictly explain, much simultaneous modification.
Anyhow, we see in our domestic varieties the very same fact: though our domestic
races may differ much in some one organ from the other races of the same species, yet the other
parts of the organisation will always be found in some degree different.
Professor Bronn likewise asks with striking effect how, for instance in the mouse or hare genus, natural selection will
account for the several species (descended, I may remark, from a parent of unknown character) having longer or shorter tails, longer or shorter ears, and fur of different colours; how will
it account for one species of plant having pointed and another species obtuse
leaves?
I can give no definite answer to such questions; but I might ask in return, were these differences, on the doctrine of independent creation, formed for no purpose?
If of use, or if due to correlation of growth, they could assuredly be formed through the natural preservation of such useful or correlated variations.
I believe in the doctrine of descent with modification, notwithstanding that this or that particular change of structure cannot be accounted for, because this doctrine groups together and explains, as we shall see in the latter
chapters, many general phenomena of nature.
A distinguished botanist, Mr. H. C. Watson, believes that I have overrated the importance of the principle of divergence of character (in which, however, he apparently believes), and that convergence of character, as it may be called, has likewise played a part.
This is an intricate subject which need not be here discussed.
I will only say
that if two species of two closely allied genera produced a number of new and divergent species, I can believe that these new forms might sometimes approach each other so closely that they would for convenience
sake be classed in the same new genus, and thus two genera would converge into one; but from the strength of the principle of inheritance, it seems hardly credible that the two groups of new species would not at least form two sections of the supposed new single genus.
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