"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, &c., 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, by 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 Kölliker'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 Kölliker enumerates and discusses are the
following: [Footnote: Space will not allow us to give Professor Kölliker'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 Kölliker 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 Kölliker 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, Kölliker, 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 Kölliker'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 state, 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
civilisation 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 Kölliker replies, with perfect justice, that the
conclusion drawn by Pelzeln does not really follow from Darwin's premises,
and that, if we take the facts of Paleontology 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-fertilisation 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_ p.
82).