THE GENERIC THEORY.
How glorious to the observant eye is the great system of the organic
world, how perfect in each separate part, how complete and harmonious
the whole! The unity of the comprehensive plan, amidst the infinite
modifications which it includes, has ever been a theme of admiration
and delight; for the mind, which has once caught a glimpse, even in
physics, of what it is not possible to disprove, instinctively clings
to it, as to a grand material truth. The discovery, at all times, of
what we feel to be actually _certain_ is in itself so fascinating,
that the very data which it gives us are scarcely more prized than the
mere knowledge that we have gained a single additional light to guide
us on our forward way: for, since in the inductive sciences we can but
climb from step to step, at a slow and even pace, we hail with inward
satisfaction whatsoever may tend to lighten our task, and to lead us
more quickly onwards (gradually though we must of necessity advance)
towards its final accomplishment.
But how, it may be asked, is this general harmony of the organic
creation to be insisted upon, when beings so extravagant and
dissimilar are everywhere to be met with? Is it possible to recognize
anything like a unity of type amongst creatures so differently
constructed, and so widely removed from each other in their habits,
aspects, functions, and attributes? Such questions as these, however,
though they may occasionally perplex the tyro, or amateur, are not
likely to be raised by anyone who has mastered the merest alphabet of
zoology,--and who is aware that the integrity of Nature is something
real and positive, as experience indeed is ever tending more and more
to corroborate, and by no means the day-dream of an enthusiastic, or
fertile, imagination. To trace out the progressive development of
animal life, from its humblest phases; and to mark, as they become
visible in the intermediate grades, the first rudiments of organs and
instincts which are destined to attain their maximum in the higher
ones, embody but a small portion of what it is the naturalist's
mission to investigate. To him belongs the special privilege of
inquiring dogmatically into this structural advancement; and of
suggesting methods of classification which shall accord, in their
several component divisions, so far at least as is practicable, with
the constitutional change. We should recollect, however, that this
system, being based upon truth, must, if it would be consonant
throughout, adapt itself to all the various phaenomena (in their
respective positions, in the scale), from the consideration of which
it should be exclusively deduced, or built. To draw broad conclusions
of any kind, or to attempt the establishment of propositions and
principles, from simple dialectics, without a previous training in
the practical bearings of the subject, would be absurd, and almost
certain to beget error. "It cannot be that axioms established by means
of _reasoning_ [alone] should be of any value for the discovery of new
results; because the subtilty of Nature far exceeds the subtilty of
reasoning. But axioms duly and orderly abstracted from _particulars_,
in their turn easily point out and mark off new particulars; and so
render the sciences active[78]." Such were the words of the greatest
philosopher which this country has ever produced; and it would be
well, whilst examining the causes of what we see, and endeavouring to
obtain some faint and distant notion of the vast scheme of Nature as
originally designed, to keep them constantly in view,--lest, by
trusting to theory only, apart from observation and facts; or by
venturing to pervert the latter (instead of being led by them), so as
to tally with our preconceived ideas of what ought to be, we miss our
road, and become lost in the mazy labyrinth of our own fanciful
inventions.
With this preliminary stricture on the express duty which devolves
upon the naturalist (with whom the phaenomena of the organic world
principally rest, for interpretation) to make facts, rather than
reason and argument, the basis of his various doctrines,--at any rate
of those in which the critical subject of _arrangement_ is concerned;
I shall perhaps be pardoned, after having been drawn, in the preceding
chapters (however involuntarily), into the question of 'species,' as
rigidly defined, if I now offer a few passing remarks on the theory of
_genera_.
There can be no doubt that amongst a large class of ordinary observers
a clear perception of the generic system, in an abstract sense, does
not by any means prevail. What the nature of a genus really is, would
appear to have been very commonly overlooked, or perhaps
misunderstood, by people of this stamp; and the consequence has been,
that the wildest notions have frequently arisen, even from men of
sound _specific_ attainments, as to the claims (for annihilation or
retention, as 'genera') of certain subsidiary zoological assemblages.
The terms 'genus' and 'species' have been conjointly so long
associated in our minds with the selfsame things (whatsoever they may
be), that they have become almost part and parcel of the objects
themselves; so that the student who does not sufficiently reflect on
their true signification, is apt to regard them as of equal
importance,--or, rather, more often perhaps than otherwise, to make
the latter subservient (or inferior) to the former! This however is,
in reality, the very reverse of what should be the case, as a moment's
consideration will indeed at once convince us: for what are genera,
after all, but _dilatations_ (as it were) along a chain _which is
itself composed of separate_, though differently shaped, _links_? The
links (or the actual, independent bodies which constitute the chain)
are the species; but the knobs, or swellings, which their several
forms may tend, _by degrees_, to establish along its course (through
the slight disparity which each of them presents from that which is
next in succession to it; and therefore through the gradual manner in
which the bulbs, or nodules, may be said, _on the whole_, to be
produced), are the groups into which those species naturally fall. It
matters not a straw whether these assemblages be primary, secondary,
tertiary, &c.,--in other words, whether they be departments, families,
or genera, as usually understood,--the _principle_ is in every
instance the same; the difference being merely relative, and not
absolute.
Or, if we choose to vary the simile, we may compare the whole system
to a cord, upon which beads, of innumerable sizes, patterns, and
colours, have been densely strung. Now, if there were no such things
as natural divisions in the organic world, these beads (which
represent the separate species) might have been disposed of
anyhow,--their positions, with respect to each other, would under
those circumstances have been of no importance. But such is not the
case: there is an order and method throughout Nature, which shows that
every individual portion of it has been adjusted by the Master's hand,
and that nothing has been left to chance. Those beads (to follow up
the metaphor) of countless magnitudes and hues, have had their proper
places allotted to them,--and moreover with such care and regularity,
that a complete plan, or scheme, of distribution is at once
conspicuous. Although there are not even two, amongst that enormous
multitude, which are _precisely_ alike (for every species, however it
may resemble its next ally, has _some_ distinctive feature of its
own), we immediately perceive that those beads which have most in
common, are, as it were, attracted to each other,--so as, by their
close approximation, or contact, to create excrescences and stripes,
of divers kinds, along the entire length of the cord. If we assume now
that the red beads have been collected together, to the length (for
instance) of a yard, and that within that space a dozen protuberances,
of discordant aspects and dimensions, have (by the union of those
beads which more nearly simulate each other) been brought about; we
shall have a very fair idea of the ordinary grouping of the animate
tribes. The red beads, taken in the mass, may be likened to a perfect
"family;" the differing gibbosities to twelve well-marked "genera,"
which that family includes; whilst the "species" (the real _dramatis
personae_, of independent existence, which are nevertheless compelled
to occupy the situations we have described,--thus _causing_ the
divisions to be mapped out) are here typified, as everywhere, by the
several beads themselves.
I have not thought it necessary to pursue this reasoning into higher
divisions than "families;" but of course it may be extended to any
amount,--so as to shadow forth, equally, the compartments of
_primary_ significance. Nor would I wish to imply, by the above
similes, that I regard a _lineal_ method of arrangement as the correct
one. Every zoologist is aware, that in Nature such does not exist: but
the mode of illustration which I have selected is applicable to all
systems alike, so far as the _principle_ is concerned.
It will consequently be seen, from what has been said, that the terms
"genus" and "species" not only differ very considerably in
_importance_, but in signification also. Whilst the former is merely
suggestive of a particular _position_ which a creature occupies in a
systematic scale (a position, however, which depends upon the various
structural peculiarities which it possesses _in common with other
beings_,--which thus more or less resemble it); the latter expresses
the actual creature itself: so that while one applies to _several_
animals (of distinct natures and origins, though bound together by a
certain bond of imitation), the other belongs to _a single race
alone_, which it therefore exclusively indicates. But if such be the
case, it will perhaps be asked,--Why then insist upon a generic name
at all, if the specific one be sufficient to denote all that is
required, namely, the _animal itself_? To which, however, we may
reply, that the binomial nomenclature is demanded for two elementary
reasons,--first, because it is founded upon a natural truth, which (to
say the least) it would be unwise to violate; and, secondly, because
it is _convenient_, both for simplification and analysis. We should
assuredly be surprised were a man to object to his surname, as
unnecessary, because he has a christian (or specific[79]) one which is
the exponent of him _alone_. True it is that his family (or generic)
title applies to the rest of his kin also; but, since there are other
people (of other families) who may have the same _individual_
appellation as himself, it is clearly desirable, even as a matter of
expediency alone, that patronymic and christian name should be alike
retained. We need not, however, plead expediency, in favour of this
acceptance of what has been so long tested, and shown to be correct;
we appeal to a higher tribunal,--that of experience,--in proof that it
draws its origin from Nature itself, and is implied by the very
existence, or reality, of _natural groups_. The 'Methode Mononomique'
has indeed been attempted[80]; and it has failed,--or at any rate it
has shown itself to be inferior, both ideally and in practice, to the
plan commonly in use: and if I might be pardoned a passing conjecture
on its ultimate success, I should be inclined, since it is contrary to
the canon of the organic world, to regard its case as utterly
hopeless.
Let us not be unfair, however, towards those who have sought to
establish a nomenclature which they conceived would be less open to
objections than that which we have been hitherto accustomed to
endorse. The notion did, at any rate, arise out of an apparent defect
in the binomial process,--for the inconveniences which they complained
of are real ones; and, having felt them practically, they aspired to
sweep them away by remodelling the whole system afresh. But, had it
not been for an evident misconception of the generic theory, in the
abstract, the trial would in all probability have never been made; and
we should have been spared the downfall of a contrivance which has had
but little to recommend it beyond the ingenuity of its machinery and
detail. If we analyse the motives for this experiment, we shall find
that it originated from a belief, that genera are _either_ purely
imaginary, or else that they must (like species) have a definite and
isolated existence. Now both of these conclusions appear to be equally
gratuitous and untenable; and such as a lack of observation could
alone beget. Genera are _not_ mere phantoms of the brain (as most
naturalists will readily admit); but they are, likewise, by no means
abrupt, or well-marked, on their outer limits (except indeed by
accident,--of which hereafter), but merge into each other by
gradations, more or less slow and perceptible. Such being the case, we
can easily understand why it is that the followers of the 'Methode
Mononomique' (who, paralysed by the fact that genera are seldom
_clearly defined at their extremes_, would seem to repudiate them _in
toto_) have rashly regarded the binomial system as intolerable.
Finding that it was possible for numerous species, whose structural
characteristics were less conspicuously pronounced than those of
their allies, to be enumerated, and with equal plausibility, under two
consecutive groups; they immediately inferred that the groups
themselves could not be upheld on account of these connective links:
and so it was resolved (through a new and artificial scheme) to ignore
them; and to fall back upon the creed, that species alone (and not
genera) are to be recognized in the organic world. This was but the
device, however, at the outset, of a single mind; and the perverts to
it have been but few. It is in direct opposition to the first
principles of nomenclature, and sets at defiance a great natural
truth.
But what, it may be inquired, is this great primary truth which the
monomial system tends to violate? I repeat what I have already stated,
that it is the _existence of natural assemblages_ which that scheme
would, if it were practicable, discountenance. Order and symmetry,
however (which involve classification, or arrangement), are the law of
Nature, and it is not possible to set them aside. It matters not if
harsh lines of demarcation are undiscernible between the several
consecutive groups,--the _groups themselves_ must still remain
(however equivocal it may be where they exactly commence or
terminate), and cannot be wiped out. To suppose _a priori_ that the
allied divisions of the animate creation are perfectly disconnected
_inter se_, is in fact to break the chain on which the unity of the
organic world depends; whilst to assume that groups cease to be groups
when they can be discovered to merge into each other, would no less
destroy the harmony of that admirable method, or array, which the
naturalist, above all others, delights to contemplate. If things are
no longer to be regarded as dissimilar because they unite on their
outer limits, differences may be given up, as having no special
meaning, and as therefore unworthy of investigation. It requires but a
slight insight into the physical universe to be convinced, that nearly
everything which we see (and, moreover, _without injuring its
individual reality_) is blended into that to which it is the most
akin. Night is distinct from day; yet, so long as the twilight
intervenes, no man can pronounce where the one ends, and the other
begins. Heat is opposed to cold; yet, if by degrees they be
respectively diminished, they will at last amalgamate, in a central
temperature. And thus it is with things material. The sea and the land
are essentially unlike; yet the precise boundary between the two is
never clearly defined,--the ebb and flow are constantly going on, and
the line of separation is variable. The mountain-range is moulded on a
different type to the level country beneath it; yet the turning-point
of them both is, in all instances, on neutral ground. We need not
however adduce further evidence in support of this fact,--that,
throughout the whole of Nature, the _general principle_ of fusion
(either absolute or apparent) is most obvious. From first to last,
traces of it are everywhere to be detected; not only between
_clusters_, or material combinations, of objects (in which case it is
absolute), but even between the objects themselves,--under which
circumstances, however, it is merely apparent; for, since they are
specifically dissimilar, it can only arise from their _near
resemblance_ to each other, and not from their positive coalescence.
But, admitting that this universal blending, throughout the animate
world, does not interfere with the gradual conformation of its several
groups, which _therefore_ should be recognized; we may perhaps be told
by the believers in the 'Methode Mononomique,' that they do not intend
to ignore the _arrangement_ which Nature has so broadly laid down, but
that, on the contrary, they tacitly endorse it,--their device having
reference to the _names_ only. To this however it will be sufficient
to reply, that, if they deem it necessary (of which I am by no means
convinced) to accept the natural genera of the organic creation at
all, why not _acknowledge_ them? and how can they be so well
acknowledged, either in principle or practice, as through the medium
of a binomial nomenclature? Such a system is the only consistent one,
on the hypothesis that they _do_ consider them of primary importance;
it is more in unison with our notions of what ought to be; more
suggestive of what actually _is_; more honest and generous to those
who have laboured (as describers), with such care and diligence,
before us.
It will be perceived, from the above remarks, that, although
professedly criticizing the 'Methode Mononomique,' into the analysis
of which my subject has unintentionally drawn me, it is the absurdity
of objecting to genera _because they are not rigidly defined
throughout_, that I have been mainly striving to condemn. It is
indeed well nigh incredible that any such strictures could ever have
been advanced; for it must surely have occurred to the most
superficial inquirer, that genera, after all, _cannot_ be
homogeneous,--seeing that they are necessarily composed of detached
species, no two of which are _precisely_ similar, even in the few
structural details which may have been accidentally chosen for generic
diagnostics. How is it possible, therefore, that mere _groups_, even
though they be in accordance with Nature, should be so far isolated
and uniform in their character as to occupy an analogous position to
that of the absolutely independent species (of distinct origins) which
they severally contain?
Taking the preceding considerations into account, the question will
perhaps arise,--How then is a genus to be defined? To which I may
reply that, were I asked whether genera had any real existence in the
animate world, my answer would be that they undoubtedly have,--though
not in the sense (which is so commonly supposed) of abrupt and
disconnected groups. I conceive them to be gradually formed nuclei,
through the gathering together of creatures which more or less
resemble each other, around a central type: they are the _dilatations_
(to use our late simile) along a chain which is itself composed of
separate, though differently shaped links,--the links being the actual
species themselves, and the swellings, or nodes, the slowly developed
genera into which they naturally fall. When I say "slowly developed,"
my meaning may possibly require some slight comment. It is simply
therefore to guard against the fallacy, which I have so often
disclaimed, that genera are abruptly (or suddenly) terminated on their
outer limits, that the expression has been employed. Though I believe
that a series of _species_, each partially imitating the next in
contact with it, is Nature's truest system; yet we must be all of us
aware that those species do certainly tend, in the main, to map out
assemblages of divers phases and magnitudes, distinguished by peculiar
characteristics which the several members of each squadron have more
or less in common. So that it is only in the middle points that these
various groups, respectively, attain their maximum,--every one of
which (by way of illustration) may be described as a _concentric
bulb_, which becomes denser, as it were, in its successive component
layers, and more typical, as it approaches its core.
If, then, the theory of genera be such as I have endeavoured to
expound, it results from what has been said, _that every generic type
is to be looked for in, or about, the centre of its peculiar
group_,--or at any rate in that region of it which would seem to be
the most characteristically, or evenly, pronounced. I lay particular
stress upon this conclusion, because (if correct) it will somewhat
modify the notions which are occasionally entertained upon the
subject. A stricture, however, may here be required upon what I have
advanced, lest, through using the metaphors _which I selected for the
elucidation of a principle_, it be supposed that I would wish them to
apply to the smaller details, likewise, of the problem. If a genus has
been portrayed under the similitude of a bulb, or of a nodule (formed
by the approximation of beads which more or less resemble each other
in their primary aspect), it does not follow that either bulb or
nodule are to diminish in a similar ratio towards their respective
circumferences,--or, which is the same thing, that they are to be
symmetrical; whether spherical, ovoid, or otherwise. The general
method of the organic creation is a progressive one; and its
successive types, therefore, will not always be found to radiate
_equally_ from their normal foci: so that it is in the direction of
the _higher_ (rather than the lower) extremities of the assemblages
that those foci are usually to be discerned;--and where the groups are
large, it is not often difficult to pronounce which of their ends are,
as a whole, the more perfectly developed.
It will, moreover, be further acknowledged (if my premises are
allowed), that, since it is a somewhat central position which the
typical member of a genus usually occupies, _the diagnostic
characters_, although (in combination) carried out to the full, _are
more evenly balanced in a generic type than in any of its associates_;
or, in other words, that a species in which any single organ is
monstrously enlarged, at the expense of the rest, is seldom typical of
the assemblage with which it is placed; but may be _a priori_ regarded
as in all probability a transition form, leading us onwards into some
neighbouring group[81].
I will not, however, venture too closely into this question in its
minor bearings;--suffice it to have demonstrated that, whatever be the
rate, law, or direction, of the advancement of the various groups
towards a more perfect model; or in whatsoever position the several
types are to be discerned, with respect to their immediate associates,
genera _cannot_ be isolated and distinct, but must of necessity merge
(each into two or more others) on their outer limits. Hence, if such
be the case, as I contend that it usually is (the exceptions to the
rule being, as I shall hope shortly to prove, the result of accident,
and by no means a part of the original design), it may perhaps be a
problem, how far we are justified in rejecting many large and natural
assemblages, through the fact that they blend, both at their
commencement and termination, imperceptibly, with others,--their
precise boundaries being dimly defined.
That the recognition of genera is necessary, even as a matter of mere
convenience, is self-evident; for in many extensive departments they
combine with each other so completely at their extremities (although
sufficiently well-marked in the mass), that, unless we are prepared
to accept them as they are, we must needs repudiate them altogether:
under which circumstances, our difficulties, both in determination and
nomenclature, would be increased tenfold. We should also recollect,
that clusters which seem abruptly chalked out whilst our knowledge is
imperfect, are very frequently united with others when fresh
discoveries are made, and the intermediate grades brought to light: so
that their apparent isolation may oftentimes arise from our ignorance
of the absent links, rather than from the fact itself. It would surely
be more desirable, therefore, when viewed even in the light of
expediency alone, to submit to the possibility of a few neutral
species being conceded, _with equal reason_, to different groups, than
to amalgamate the whole, and so lose sight of the general method or
arrangement, into which the various creatures do unquestionably (in a
broad sense) dispose themselves. If, however, there be any truth in
the generic doctrine as above enunciated, the question of
_convenience_ may be omitted from our speculations _in toto_,--seeing
that _all_ genera (except those whose present abruptness is the effect
of accident) fuse into others with which they are in immediate
contact: so that in reality, unless we ignore these natural
assemblages from first to last, we have no choice left us as regards
the equivocal forms; but must consent to recognize them as of doubtful
location, and as possessing an equal right to be placed in one or the
other of two consecutive groups,--according to the judgment of the
particular naturalist who has to deal with them.
But let us glance at the subject through the medium of an example, and
endeavour to realize what would be the consequence of that wholesale
combination at which we must sooner or latter arrive, if genera are
not to be upheld because they slowly merge into each other as we
recede from their respective types. The immense department _Carabidae_,
of the Coleoptera, is eminently a case in point. In the details of
their oral organs the _whole_ of that family display (as I have
elsewhere[82] remarked) so great a similarity _inter se_, or rather
shade off into each other by such imperceptible gradations, that the
_tendency_ which various clusters of them possess to assume
modifications of form which attain their maximum only in successive
centres of radiation, must oftentimes be regarded as _generic_, if we
would not shut our eyes altogether to the natural collective masses
into which the numerous species (however gradually) are, in the main,
so manifestly distributed. It is possible indeed that, as our
knowledge advances and new discoveries take place, we shall so far
unite many of the consecutive nuclei which are now considered pretty
clearly defined, that we shall be driven at last _either_ to accept
the Linnaean genera only, or else the entire host of subsidiary ones
(albeit perhaps in a secondary sense) which are, one by one, being
expunged. And, since under the former contingency the _determination
of species_ would become practically well nigh hopeless, it is far
from unlikely that we shall eventually hail the latter as, after all
(at any rate to a certain extent), the more convenient of the two.
Look, for instance, at the great genus _Pterostichus_, which has
nearly 200 representatives in Europe alone: true it is that its
several sections (_Poe cilus_, _Argutor_, _Omaseus_, _Corax_,
_Steropus_, _Platysma_, _Cophosus_, _Pterostichus_ proper, _Abax_,
_Percus_, and _Molops_), although easily recognized in the mass, do
unquestionably blend into each other; yet I believe that it has arisen
from a too rigid promulgation of the generic theory that they have not
been retained as separate. And this opinion may be rendered somewhat
more plausible, from the knowledge that certain of the _Pterostichi_
(the Argutors, for instance) approach so closely, in their trophi, to
_Calathus_, as to be hardly discernible from it; which latter genus is
scarcely distinguishable (structurally) from _Pristonychus_,--a form
which, in its turn, leads us on towards another type. Who would have
imagined, again, some fifty years ago, that the widely distributed
groups, _Calosoma_ and _Carabus_, were not thoroughly detached _inter
se_? yet what naturalist _now_ can draw an exact line of demarcation
between them? And so it is with numerous others, which it is needless
to recall. The practical inference, however, from the whole, is this:
_that if genera must be rejected because they are not homogeneous and
isolated throughout, the only ones that will remain are those which
have become abrupt from causes which are merely accidental_.
Having now, however, examined the question in its broadest phasis,
that is to say, on the supposition that Nature is _complete_ in her
several links and parts; I shall perhaps be expected to offer a few
passing words on what I have already hinted at,--namely, the
possibility of genera being absolutely well-defined, even on their
outer limits, _from accident_. Briefly, then, it is through the
extinction of species that groups may, in some instances, be abruptly
expressed: but, as such contingences are at all times liable (whether
from natural or artificial causes) to happen; it would be unfair to
build up our generic _definition_ from examples which are the
exception, and not the rule,--and, _more_ than mere "exceptions" (as
commonly understood by that term), the result of positive disturbances
from without. Yet, that genera thus distinctly bounded, at either end,
do actually occur, must be self-evident to any one who has attempted
to study the distribution of organic beings with reference to the
geological changes which have taken place on the earth's surface; for
it is clear that a vast proportion of the creatures which inhabit our
globe came into existence at periods _anterior_ to many of those great
convulsions which altered finally the positions of sea and land,
apportioning to each the areas which they now embrace: so that, if
_generic provinces_ of radiation (no less than specific centres) be
more than a fancy or romance, it is certain that numerous members of
many geographical assemblages must have perished for ever during the
gigantic sinkings which have at various epochs been brought about.
From which it follows, _that those groups, or clusters, of which but
few representatives (comparatively) are extant, will be more or less
abruptly terminated, according as the original type to which they
severally belong was peculiar, and in proportion as the number of its
exponents has been reduced_.
Although there are many means through which species may become
annihilated, yet, since the subsidence of a tract into the sea
involves the maximum of loss which a space of that magnitude can
sustain, the above conclusion gives rise to a corollary: _that it is
in islands that we should mainly look for genera which are to be
rigidly pronounced_. The question therefore naturally suggests
itself,--Is this in harmony with what we see; or, in other words, is
it consistent with experience, or not? I believe that it is; for I
think it will be found, on inquiry, _that the greater proportion of
those groups which are more especially isolated in their character_ (I
do not say, necessarily, the most anomalous; though this in some
measure follows from the fact of their detachment) _are peculiar to
countries which are insular_.
But, however important an element, in the eradication of species,
submergence may be; we must not entirely omit to notice other methods
also, through the medium of which genera may become well-defined. We
should recollect that the removal of a _very few_ links from an
endemic cluster is sufficient to cause its disjunction from the type
to which it is next akin, and that where the creatures which unite in
composing it are of slow diffusive powers, or sedentary habits, the
elimination of such links is (through the smallness of the areas which
have been overspread) a comparatively easy operation. The accidental
introduction of organic beings amongst others to the interests of
which they are hostile, may be a powerful means, as Mr. Darwin has
suggested, of keeping the latter in check, and of finally destroying
them[83]. The gradual upheaval of a tract which has been well-stored
with specific centres of radiation, created expressly for itself, may
(through the climatal changes which have been brought about) succeed
in extirpating races innumerable,--those only surviving which are able
to adapt themselves to the altered conditions; and which would _now_
be consequently looked upon as abrupt topographical assemblages. The
over-whelming effect of a volcanic eruption, in a region where the
aborigines of the soil have not wandered far from their primaeval
haunts, may, as Sir Charles Lyell has well remarked, put an end to
others, and so effect the separation of their allies from the central
stock. And, lastly, the intervention of man, with all the various
concomitants which civilization, art, and agriculture bring in his
train, is the most irresistible of every agency in the extensive
(though often accidental) demolition of a greater or less proportion
of the animate tribes.
The whole of these ultimate assortments, however, are dependent, as it
were, for their outline, upon contingency or chance; and we must not
deduce our ideas of genera from the examples which _they_ supply. We
should rather reflect, that it is no matter of mere speculation, that
many organic links, now absent, have, through the crises and
occurrences to which we have just drawn attention, become lost. On the
contrary, indeed, we know that, in the common course of things, it
_must_ have been so; and therefore we are induced to regard those
cases as exceptional, and as in no way expository of Nature's
universal scheme. The more we look into the question, whether by the
light of analogy or the evidence of facts, the more are we convinced
that lines of rigid demarcation (either between genera or species,
though especially the former) do not anywhere, except through
accident, exist. And hence it is that we ascend, by degrees, to a
comprehension of that _unity_ at which I have already glanced; and
are led to believe that, could the entire living panorama, in all its
magnificence and breadth, be spread out before our eyes, with its
long-lost links (of the past and present epochs) replaced, it would be
found, from first to last, to be complete and continuous
throughout,--a very marvel of perfection, the work of a Master's
hand.
FOOTNOTES:
[78] "Nullo modo fieri potest, ut axiomata per argumentationem
constituta ad inventionem novorum operum valeant; quia subtilitas
naturae subtilitatem argumentandi multis partibus superat. Sed axiomata
a particularibus rite et ordine abstracta, nova particularia
rursus facile indicant et designant; itaque scientias reddunt
activas."--_Novum Organum_, Aphoris. xxiv.
[79] In selecting this simple method to illustrate the _principle_ of
a binomial system of nomenclature, it is scarcely necessary to remind
the reader that I do not intend to imply that every man is
_specifically distinct_ from his neighbour!
[80] Considerations sur un Nouveau Systeme de Nomenclature, par C. J.
B. Amyot (_Rev. Zool._, p. 133, A.D. 1838).
[81] I may add, that this suggestion, as to the evenly balanced state
of generic types, is in accordance with the views of Mr.
Waterhouse,--whose extensive knowledge in the higher departments of
zoological science gives a value to his opinion, especially on
questions such as these, which I am glad to have an opportunity of
acknowledging.
[82] Annals of Nat. Hist. (2nd series), xiv., p. 199.
[83] A familiar example of this disappearance of a creature before the
aggressive powers of another, which is either hostile to or stronger
than itself, is presented by the Black Rat (_Mus rattus_) of our own
country,--which is said to have been extremely abundant formerly, but
which is now replaced by the common brown (or "Hanoverian") one of
Northern Europe. The British species, however, although it has become
extremely scarce, is not yet _quite_ exterminated: it has been
recorded (_vide_ 'Zoologist,' 611) in Essex, and in Devonshire
('Zoologist,' 2344); and it still swarms on a small rock off Lundy
Island, in the Bristol Channel. It is reported, moreover, to have been
lately re-introduced at Liverpool.