"Our ignorance of the laws of variation is profound. Not in one case out
of a hundred can we pretend to assign any reason why this or that part
varies more or less from the same part in the parents...The external
conditions of life, as climate and food, etc., seem to have induced some
slight modifications. Habit, in producing constitutional differences,
and use, in strengthening, and disuse, in weakening and diminishing
organs, seem to have been more potent in their effects."
And finally, as if to prevent all possible misconception, Mr. Darwin
concludes his Chapter on Variation with these pregnant words:--
"Whatever the cause may be of each slight difference in the offspring
from their parents--and a cause for each must exist--it is the steady
accumulation, through natural selection of such differences, when
beneficial to the individual, that gives rise to all the more important
modifications of structure which the innumerable beings on the face of
the earth are enabled to struggle with each other, and the best adapted
to survive."
We have dwelt at length upon this subject, because of its great general
importance, and because we believe that Professor Kolliker's criticisms
on this head are based upon a misapprehension of Mr. Darwin's
views--substantially they appear to us to coincide with his own. The
other objections which Professor Kolliker enumerates and discusses are
the following*:--([Footnote] *Space will not allow us to give Professor
Kolliker's arguments in detail; our readers will find a full and
accurate version of them in the 'Reader' for August 13th and 20th,
1864.)
"1. No transitional forms between existing species are known; and
known varieties, whether selected or spontaneous, never go so far as to
establish new species."
To this Professor Kolliker appears to attach some weight. He makes the
suggestion that the short-faced tumbler pigeon may be a pathological
product.
"2. No transitional forms of animals are met with among the organic
remains of earlier epochs."
Upon this, Professor Kolliker remarks that the absence of transitional
forms in the fossil world, though not necessarily fatal to Darwin's
views, weakens his case.
"3. The struggle for existence does not take place."
To this objection, urged by Pelzeln, Kolliker, very justly, attaches no
weight.
"4. A tendency of organisms to give rise to useful varieties, and a
natural selection, do not exist.
"The varieties which are found arise in consequence of manifold external
influences, and it is not obvious why they all, or partially, should be
particularly useful. Each animal suffices for its own ends, is perfect
of its kind, and needs no further development. Should, however, a
variety be useful and even maintain itself, there is no obvious
reason why it should change any further. The whole conception of the
imperfection of organisms and the necessity of their becoming perfected
is plainly the weakest side of Darwin's Theory, and a pis aller
(Nothbehelf) because Darwin could think of no other principle by which
to explain the metamorphoses which, as I also believe, have occurred."
Here again we must venture to dissent completely from Professor
Kolliker's conception of Mr. Darwin's hypothesis. It appears to us to be
one of the many peculiar merits of that hypothesis that it involves no
belief in a necessary and continual progress of organisms.
Again, Mr. Darwin, if we read him aright, assumes no special tendency of
organisms to give rise to useful varieties, and knows nothing of
needs of development, or necessity of perfection. What he says is, in
substance: All organisms vary. It is in the highest degree improbable
that any given variety should have exactly the same relations to
surrounding conditions as the parent stock. In that case it is either
better fitted (when the variation may be called useful), or worse
fitted, to cope with them. If better, it will tend to supplant the
parent stock; if worse, it will tend to be extinguished by the parent
stock.
If (as is hardly conceivable) the new variety is so perfectly adapted
to the conditions that no improvement upon it is possible,--it will
persist, because, though it does not cease to vary, the varieties will
be inferior to itself.
If, as is more probable, the new variety is by no means perfectly
adapted to its conditions, but only fairly well adapted to them, it will
persist, so long as none of the varieties which it throws off are better
adapted than itself.
On the other hand, as soon as it varies in a useful way, i.e. when the
variation is such as to adapt it more perfectly to its conditions, the
fresh variety will tend to supplant the former.
So far from a gradual progress towards perfection forming any necessary
part of the Darwinian creed, it appears to us that it is perfectly
consistent with indefinite persistence in one estate, or with a gradual
retrogression. Suppose, for example, a return of the glacial epoch and a
spread of polar climatal conditions over the whole globe. The operation
of natural selection under these circumstances would tend, on the whole,
to the weeding out of the higher organisms and the cherishing of the
lower forms of life. Cryptogamic vegetation would have the advantage
over Phanerogamic; Hydrozoa over Corals; Crustacea over Insecta, and
Amphipoda and Isopoda over the higher Crustacea; Cetaceans and Seals
over the Primates; the civilization of the Esquimaux over that of the
European.
"5. Pelzeln has also objected that if the later organisms have proceeded
from the earlier, the whole developmental series, from the simplest to
the highest, could not now exist; in such a case the simpler organisms
must have disappeared."
To this Professor Kolliker replies, with perfect justice, that the
conclusion drawn by Pelzeln does not really follow from Darwin's
premisses, and that, if we take the facts of Palaeontology as they
stand, they rather support than oppose Darwin's theory.
"6. Great weight must be attached to the objection brought forward by
Huxley, otherwise a warm supporter of Darwin's hypothesis, that we know
of no varieties which are sterile with one another, as is the rule among
sharply distinguished animal forms.
"If Darwin is right, it must be demonstrated that forms may be produced
by selection, which, like the present sharply distinguished animal
forms, are infertile, when coupled with one another, and this has not
been done."
The weight of this objection is obvious; but our ignorance of the
conditions of fertility and sterility, the want of carefully conducted
experiments extending over long series of years, and the strange
anomalies presented by the results of the cross-fertilization of many
plants, should all, as Mr. Darwin has urged, be taken into account in
considering it.
The seventh objection is that we have already discussed (supra).