CHAPTER XI - ON THE GEOLOGICAL SUCCESSION
OF ORGANIC BEINGS
On the State of Development of Ancient compared with Living Forms
We have seen in the fourth chapter that the degree of
differentiation and specialisation of the parts in organic beings,
when arrived at maturity, is the best standard, as yet suggested, of
their degree of perfection or highness. We have also seen that, as the
specialisation of parts is an advantage to each being, so natural
selection will tend to render the organisation of each being more
specialised and perfect, and in this sense higher; not but that it may
leave many creatures with simple and unimproved structures fitted
for simple conditions of life, and in some cases will even degrade
or simplify the organisation, yet leaving such degraded beings
better fitted for their new walks of life. In another and more general
manner, new species become superior to their predecessors; for they
have to beat in the struggle for life all the older forms, with
which they come into close competition. We may therefore conclude that
if under a nearly similar climate the eocene inhabitants of the
world could be put into competition with the existing inhabitants, the
former would be beaten and exterminated by the latter, as would the
secondary by the eocene, and the palaeozoic by the secondary forms. So
that by this fundamental test of victory in the battle for life, as
well as by the standard of the specialisation of organs, modern
forms ought, on the theory of natural selection, to stand higher
than ancient forms. Is this the case? A large majority of
palaeontologists would answer in the affirmative; and it seems that
this answer must be admitted as true, though difficult of proof.
It is no valid objection to this conclusion, that certain
brachiopods have been but slightly modified from an extremely remote
geological epoch; and that certain land and fresh-water shells have
remained nearly the same, from the time when, as far as is known, they
first appeared. It is not an insuperable difficulty that
Foraminifera have not, as insisted on by Dr. Carpenter, progressed
in organisation since even the Laurentian epoch; for some organisms
would have to remain fitted for simple conditions of life, and what
could be better fitted for this end than these lowly organised
Protozoa? Such objections as the above would be fatal to my view, if
it included advance in organisation as a necessary contingent. They
would likewise be fatal, if the above Foraminifera, for instance,
could be proved to have first come into existence during the
Laurentian epoch, or the above brachiopods during the Cambrian
formation; for in this case, there would not have been time sufficient
for the development of these organisms up to the standard which they
had then reached. When advanced up to any given point, there is no
necessity, on the theory of natural selection, for their further
continued progress; though they will, during each successive age, have
to be slightly modified, so as to hold their places in relation to
slight changes in their conditions. The foregoing objections hinge
on the question whether we really know how old the world is, and at
what period the various forms of life first appeared; and this may
well be disputed.
The problem whether organisation on the whole has advanced is in
many ways excessively intricate. The geological record, at all times
imperfect, does not extend far enough back to show with unmistakable
clearness that within the known history of the world organisation
has largely advanced. Even at the present day, looking to members of
the same class, naturalists are not unanimous which forms ought to
be ranked as highest: thus, some look at the selaceans or sharks, from
their approach in some important points of structure to reptiles, as
the highest fish; others look at the teleosteans as the highest. The
ganoids stand intermediate between the selaceans and teleosteans;
the latter at the present day are largely preponderant in number;
but formerly selaceans and ganoids alone existed; and in this case,
according to the standard of highness chosen, so will it be said
that fishes have advanced or retrograded in organisation. To attempt
to compare members of distinct types in the scale of highness seem
hopeless; who will decide whether a cuttle-fish be higher than a
bee- that insect which the great von Baer believed to be "in fact more
highly organised than a fish, although upon another type"? In the
complex struggle for life it is quite credible that crustaceans, not
very high in their own class, might beat cephalopods, the highest
molluscs; and such crustaceans, though not highly developed, would
stand very high in the scale of invertebrate animals, if judged by the
most decisive of all trials- the law of battle. Besides these inherent
difficulties in deciding which forms are the most advanced in
organisation, we ought not solely to compare the highest members of
a class at any two periods- though undoubtedly this is one and perhaps
the most important element in striking a balance- but we ought to
compare all the members, high and low, at the two periods. At an
ancient epoch the highest and lowest molluscoidal animals, namely,
cephalopods and brachiopods, swarmed in numbers; at the present time
both groups are greatly reduced, whilst others, intermediate in
organisation, have largely increased; consequently some naturalists
maintain that molluscs were formerly more highly developed than at
present; but a stronger case can be made out on the opposite side,
by considering the vast reduction of brachiopods, and the fact that
our existing cephalopods, though few in number, are more highly
organised than their ancient representatives. We ought also to compare
the relative proportional numbers at any two periods of the high and
low classes throughout the world: if, for instance, at the present day
fifty thousand kinds of vertebrate animals exist, and if we knew
that at some former period only ten thousand kinds existed, we ought
to look at this increase in number in the highest class, which implies
a great displacement of lower forms, as a decided advance in the
organisation of the world. We thus see how hopelessly difficult it
is to compare with perfect fairness such extremely complex
relations, the standards of organisation of the imperfectly-known
faunas of successive periods.
We shall appreciate this difficulty more clearly, by looking to
certain existing faunas and floras. From the extraordinary manner in
which European productions have recently spread over New Zealand,
and have seized on places which must have been previously occupied
by the indigenes, we must believe, that if all the animals and
plants of Great Britain were set free in New Zealand, a multitude of
British forms would in the course of time become thoroughly
naturalised there, and would exterminate many of the natives. On the
other hand, from the fact that hardly a single inhabitant of the
southern hemisphere has become wild in any part of Europe, we may well
doubt whether, if all the productions of New Zealand were set free
in Great Britain, any considerable number would be enabled to seize on
places now occupied by our native plants and animals. Under this point
of view, the productions of Great Britain stand much higher in the
scale than those of New Zealand. Yet the most skilful naturalist, from
an examination Of the species of the species of the two countries,
could not have foreseen this result.
Agassiz and several other highly competent judges insist that
ancient animals resemble to a certain extent the embryos of recent
animals belonging to the same classes; and that the geological
succession of extinct forms is nearly parallel with the
embryological development of existing forms. This view accords
admirably well with our theory. In a future chapter I shall attempt to
show that the adult differs from its embryo, owing to variations
having supervened at a not early age, and having been inherited at a
corresponding age. This process, whilst it leaves the embryo almost
unaltered, continually adds, in the course of successive
generations, more and more difference to the adult. Thus the embryo
comes to be left as a sort of picture, preserved by nature, of the
former and less modified condition of the species. This view may be
true, and yet may never be capable of proof. Seeing, for instance,
that the oldest known mammals, reptiles, and fishes strictly belong to
their proper classes, though some of these old forms are in a slight
degree less distinct from each other than are the typical members of
the same groups at the present day, it would be vain to look for
animals having the common embryological character of the Vertebrata,
until beds rich in fossils are discovered far beneath the lowest
Cambrian strata- a discovery of which the chance is small.
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