"8. The developmental theory of Darwin is not needed to enable us to
understand the regular harmonious progress of the complete series of
organic forms from the simpler to the more perfect.
"The existence of general laws of Nature explains this harmony, even if we
assume that all beings have arisen separately and independent of one
another. Darwin forgets that inorganic nature, in which there can be no
thought of genetic connexion of forms, exhibits the same regular plan, the
same harmony, as the organic world; and that, to cite only one example,
there is as much a natural system of minerals as of plants and animals."
We do not feel quite sure that we seize Professor Kölliker's meaning here,
but he appears to suggest that the observation of the general order and
harmony which pervade inorganic nature, would lead us to anticipate a
similar order and harmony in the organic world. And this is no doubt true,
but it by no means follows that the particular order and harmony observed
among them should be that which we see. Surely the stripes of dun horses,
and the teeth of the _foetal_ _Balæna_, are not explained by the
"existence of General laws of Nature." Mr. Darwin endeavours to explain the
exact order of organic nature which exists; not the mere fact that there is
some order.
And with regard to the existence of a natural system of minerals; the
obvious reply is that there may be a natural classification of any
objects--of stones on a sea-beach, or of works of art; a natural
classification being simply an assemblage of objects in groups, so as to
express their most important and fundamental resemblances and differences.
No doubt Mr. Darwin believes that those resemblances and differences upon
which our natural systems or classifications of animals and plants are
based, are resemblances and differences which have been produced
genetically, but we can discover no reason for supposing that he denies the
existence of natural classifications of other kinds.
And, after all, is it quite so certain that a genetic relation may not
underlie the classification of minerals? The inorganic world has not always
been what we see it. It has certainly had its metamorphoses, and, very
probably, a long "Entwickelungsgeschichte" out of a nebular blastema. Who
knows how far that amount of likeness among sets of minerals, in virtue of
which they are now grouped into families and orders, may not be the
expression of the common conditions to which that particular patch of
nebulous fog, which may have been constituted by their atoms, and of which
they may be, in the strictest sense, the descendants, was subjected?
It will be obvious from what has preceded, that we do not agree with
Professor Kölliker in thinking the objections which he brings forward so
weighty as to be fatal to Darwin's view. But even if the case were
otherwise, we should be unable to accept the "Theory of Heterogeneous
Generation" which is offered as a substitute. That theory is thus stated:--
"The fundamental conception of this hypothesis is, that, under the
influence of a general law of development, the germs of organisms produce
others different from themselves. This might happen (1) by the fecundated
ova passing, in the course of their development, under particular
circumstances, into higher forms; (2) by the primitive and later organisms
producing other organisms without fecundation, out of germs or eggs
(Parthenogenesis)."
In favour of this hypothesis, Professor Kölliker adduces the well-known
facts of Agamogenesis, or "alternate generation"; the extreme dissimilarity
of the males and females of many animals; and of the males, females, and
neuters of those insects which live in colonies: and he defines its
relations to the Darwinian theory as follows:--
"It is obvious that my hypothesis is apparently very similar to Darwin's,
inasmuch as I also consider that the various forms of animals have
proceeded directly from one another. My hypothesis of the creation of
organisms by heterogeneous generation, however, is distinguished very
essentially from Darwin's by the entire absence of the principle of useful
variations and their natural selection: and my fundamental conception is
this, that a great plan of development lies at the foundation of the origin
of the whole organic world, impelling the simpler forms to more and more
complex developments. How this law operates, what influences determine the
development of the eggs and germs, and impel them to assume constantly new
forms, I naturally cannot pretend to say; but I can at least adduce the
great analogy of the alternation of generations. If a _Bipinnaria_, a
_Brachiolaria_, a _Pluteus_, is competent to produce the
Echinoderm, which is so widely different from it; if a hydroid polype can
produce the higher Medusa; if the vermiform Trematode 'nurse' can develop
within itself the very unlike _Cercaria_, it will not appear
impossible that the egg, or ciliated embryo, of a sponge, for once, under
special conditions, might become a hydroid polype, or the embryo of a
Medusa, an Echinoderm."
It is obvious, from, these extracts, that Professor Kölliker's hypothesis
is based upon the supposed existence of a close analogy between the
phænomena of Agamogenesis and the production of new species from
pre-existing ones. But is the analogy a real one? We think that it is not,
and, by the hypothesis cannot be.
For what are the phænomena of Agamogenesis, stated generally? An
impregnated egg develops into a sexless form, A; this gives rise,
non-sexually, to a second form or forms, B, more or less different from A.
B may multiply non-sexually again; in the simpler cases, however, it does
not, but, acquiring sexual characters, produces impregnated eggs from
whence A, once more, arises.
No case of Agamogenesis is known in which _when A differs widely from
B_, it is itself capable of sexual propagation. No case whatever is
known in which the progeny of B, by sexual generation, is other than a
reproduction of A.
But if this be a true statement of the nature of the process of
Agamogenesis, how can it enable us to comprehend the production of new
species from already existing ones? Let us suppose Hyænas to have preceded
Dogs, and to have produced the latter in this way. Then the Hyæna will
represent A, and the Dog, B. The first difficulty that presents itself is
that the Hyæna must be non-sexual, or the process will be wholly without
analogy in the world of Agamogenesis. But passing over this difficulty, and
supposing a male and female Dog to be produced at the same time from the
Hyæna stock, the progeny of the pair, if the analogy of the simpler kinds
of Agamogenesis [Footnote: If, on the contrary, we follow the analogy of
the more complex forms of Agamogenesis, such as that exhibited by some
_Trematoda_ and by the _Aphides_, the Hyæna must produce,
non-sexually, a brood of sexless Dogs, from which other sexless Dogs must
proceed. At the end of a certain number of terms of the series, the Dogs
would acquire sexes and generate young; but these young would be, not Dogs,
but Hyænas. In fact, we have demonstrated, in Agamogenetic phænomena, that
inevitable recurrence to the original type, which is asserted to be true of
variations in general, by Mr. Darwin's opponents; and which, if the
assertion could be changed into a demonstration, would, in fact, be fatal
to his hypothesis.] is to be followed, should be a litter, not of puppies,
but of young Hyænas. For the Agamogenetic series is always, as we have
seen, A:B:A:B, &c.; whereas, for the production of a new species, the
series must be A:B:B:B, &c. The production of new species, or genera, is
the extreme permanent divergence from the primitive stock. All known
Agamogenetic processes, on the other hand, end in a complete return to the
primitive stock. How then is the production of new species to be rendered
intelligible by the analogy of Agamogenesis?
The other alternative put by Professor Kölliker--the passage of fecundated
ova in the course of their development into higher forms--would, if it
occurred, be merely an extreme case of variation in the Darwinian sense,
greater in degree than, but perfectly similar in kind to, that which
occurred when the well-known Ancon Ram was developed from an ordinary Ewe's
ovum. Indeed we have always thought that Mr. Darwin has unnecessarily
hampered himself by adhering so strictly to his favourite "Natura non facit
saltum." We greatly suspect that she does make considerable jumps in the
way of variation now and then, and that these saltations give rise to some
of the gaps which appear to exist in the series of known forms.
Strongly and freely as we have ventured to disagree with Professor
Kölliker, we have always done so with regret, and we trust without
violating that respect which is due, not only to his scientific eminence
and to the careful study which he has devoted to the subject, but to the
perfect fairness of his argumentation, and the generous appreciation of the
worth of Mr. Darwin's labours which he always displays. It would be
satisfactory to be able to say as much for M. Flourens.
But the Perpetual Secretary of the French Academy of Sciences deals with
Mr. Darwin as the first Napoleon would have treated an "idéologue;" and
while displaying a painful weakness of logic and shallowness of
information, assumes a tone of authority, which always touches upon the
ludicrous, and sometimes passes the limits of good breeding.