THE SKULL THEORY AND THE APE THEORY.
Inasmuch as Virchow persists in treating the theory of descent as an
"unproved hypothesis," inasmuch as he ignores all the forcible
evidences of that hypothesis, he deprives himself of the right of
speaking a decisive word in this, the most important scientific
dispute of the present day. Virchow is, in fact, simply incompetent in
the great question of evolution, as he is deficient in the greater
part of that knowledge--more especially morphological knowledge--which
is indispensable to forming a judgment upon it. Hence on the
turning-point of the whole matter--viz., the problem as to the origin
of species--he can have no opinion, as he has never turned his
attention to the systematic treatment of species: those transitions of
one species into another, which he asks to see, abound on all sides,
as is well known to every systematic naturalist. Only consider, for
example, the genera of Rubus and Salix among the living plants of the
present period, and the Ammonites and Brachiopoda among extinct
animals. Hence, too, Virchow can have no independent views as to the
historical development of the higher from the lower animals, because
the abundant living forms of the lower animals are almost unknown to
him, and because he has hardly any conception of the marvellous
strides which hundreds of industrious workers have made in this very
department within the last twenty years. But there can be no doubt,
indeed it is already universally acknowledged, that it is precisely
the comparative anatomy of the lower--nay, of the very lowest
animals--that has solved the greatest riddles of life, and removed the
greatest obstacles from the path of the doctrine of descent. He simply
ignores the fact that true Monads actually exist, and have been
positively identified by many different observers as structureless
"organisms without organs," and he turns out the poor Bathybius with a
kick. And yet I believe that in "Kosmos"[15] I have conclusively proved
that Monads must retain their vast elementary importance whether the
Bathybius actually exists or not.
But even as regards the higher animals--nay, even as to the
comparative anatomy of the highest next to man, the apes--Virchow
stands apart, not understanding the views of modern morphology.
We must here examine more closely into this, because it is precisely
in this department that Virchow's only morphological experiments have
been made; viz., his investigations as to the skulls of apes and of
men. This is precisely the one only point on which he has sought a
closer acquaintance with morphology, and precisely here it is most
clearly to be seen how little he is acquainted with the recent
advances our science has made, and that he has hardly any conception
of the extraordinary importance to that science of the theory of
descent.
The skull theory, as is well known, has for a long time been a very
favourite theme, not only with prominent naturalists, but also with
talented amateurs. Undoubtedly the skull, viewed as the bony capsule
which encloses our most important organ of sense, our brain, has a
special claim to morphological importance; for the general
conformation of the skull corresponds on the whole to the development
of the brain, and its inner surface gives an approximate idea of the
outer surface of the brain. In this correspondence lies the only sound
kernel of the sickly, overgrown fancies of phrenology. The various
development of the skull allows of an approximate inference as to the
various degrees of development of the brain and of the mental
faculties. The comparative study of the skulls of the vertebrate
animals had excited the lively interest of morphologists by the end of
the last century, when comparative anatomy was beginning to
constitute a special science; and the genetic inquiry as to the
morphological significance and development of the skull soon grew out
of it. It was no less a man than our greatest German poet who first
answered this question, and propounded the theory that the skull was
neither more nor less than the modified foremost end of the vertebral
column, and that the separate groups of bones which lie behind one
another in the human skull, as in that of all the higher vertebrata,
answer to the separate modified vertebrae. This "vertebral theory" of
the skull, which Von Goethe and Oken simultaneously and independently
attempted to prove, aroused universal interest and maintained its
ground for seventy years, while many attempts were made to improve and
enlarge upon it in detail.
A quite new light was thrown on this, as on every other morphological
question, as soon as Darwin in 1859 had once more put into our hands
the torch of the doctrine of descent. The inquiry as to the origin of
the skull now assumed a real and tangible form. Since all vertebrate
animals, from fishes up to man, agree so completely as to their
essential internal structure that they can be rationally conceived of
no otherwise than as branches of one stock and as descendants of one
parent-form, the distinctly formulated question as to the skull
theory which now started into prominence was this: "How, historically,
has the skull of man and of the higher animals originated from that of
the lower animals? How is the development of the bones of the skull
from the vertebrae to be proved?" The answer to these difficult
questions was supplied by the first comparative anatomist of the
present day, by Carl Gegenbaur. After Huxley had pointed out that the
ontogenesis or individual development of the skull by no means
favoured the older hypothesis of Goethe and Oken, Gegenbaur brought
forward evidence that the fundamental idea of that theory was correct;
that the skull does in fact correspond to a series of coalescent
vertebrae, but that the separate bones of the skull are not to be
regarded as representing parts of such modified vertebrae. The
skull-bones of all recent vertebrate animals are rather, for the most
part, dermal bones, which have come into closer connection as
supplementary to the cartilaginous primitive skull. We can even now
trace the number and position of the original vertebrae, from which
this primitive skull originated, by the number of the vertebral arches
(gill-arches) which are attached to it, as well as by the number and
position of those vertebrae, from nine to ten. Of all the recent
vertebrata, the cartilaginous fishes, or Selachians, have most nearly
preserved the form and structure of this primordial skull. These
Selachians, the Rays and Sharks, are on the whole the creatures which
throw the clearest light on the history of the lineage of the
vertebrata and on the organisation of our primeval fish-natured
ancestors. It is one of the particular merits of Gegenbaur that he
clearly and firmly established the place in nature of the Selachians
as the common ancestors of all vertebrate animals from fish up to man.
None but those who have thoroughly studied the comparative morphology
of the vertebrata, who have sought the genetic issue from that
labyrinth of intricate morphological problems at the hands of the
theory of descent, can duly value the immeasurable service which
Gegenbaur has done by this and other "Investigations into the
Comparative Anatomy of the Vertebrata." These investigations are as
much distinguished by a profound knowledge and careful working out of
the wonderfully-extensive empirical materials for the subject, as by
their critical acumen and philosophic grasp. At the same time they set
in the clearest light the immeasurable value of the theory of descent
in the causal explanation of the most difficult morphological
problems. Gegenbaur might, therefore, with perfect right, enunciate
this axiom in the Introduction to his "Comparative Anatomy." "The
theory of descent will at once find a touchstone of proof in
comparative anatomy. Up to this time no experience in comparative
anatomy has transpired which contradicts that theory; on the
contrary, they all lead up to it. Thus it will receive back from
science that which it has given to scientific method: clearness and
certainty." In point of fact we can adduce no morphological
investigations which better support this declaration than those very
phylogenetic researches "as to the cranium of the Selachians, as a
basis for the critical examination of the genesis of the cranium of
the vertebrata," 1872. As Virchow had formerly thoroughly studied the
old skull-hypothesis, and in his admirable discourse on "Goethe as a
Naturalist," 1861, had given an excellent exposition of it; as
moreover he had produced most valuable contributions to the normal and
pathological anatomy of the human skull, we might have expected that
he would have received Gegenbaur's grand reform of the theory of the
skull, and historical solution of the skull-problem, with the greatest
interest, and have made it the clue to his own further researches. But
we seek in vain through Virchow's latest contributions to the study of
the human skull, for any indication of his knowing or appreciating
Gegenbaur's investigations. On the contrary, we see him persistently
moving, without any clear goal in view, on that trodden and devious
path of investigation which finds the highest aim of craniological
science in the measuring of skulls, or craniometry.
We are far from undervaluing the full significance of the results of
exact and careful descriptions and measurements of various
conformations of the skull as an empirical basis for a true and
scientific study of the skull--_i.e._, for comparative and genetic
craniology. But still we must say that the way and method by which
this skull measurement has, for ten years now, been pursued by
numerous craniologists can never yield corresponding scientific
results; on the contrary, though it is cried up as the "exact
morphology" of the skull, it simply loses itself in the domains of
harmless trifling. A large amount of time has in the last ten years
been squandered in disputes as to the best method of measuring skulls,
while the craniologists concerned have not, in the first place,
answered the obviously most important question: What end they propose
to gain by this specialist measuring, what proposition they mean to
prove by it? Most of those numerous skull measurers know nothing
beyond the perfect human skull, or at most the skulls of a few other
mammalia, while the comparative morphology and historical development
of the crania of the lower vertebrata are wholly unknown to them; and
yet these last contain the true key to the comprehension of the
others. One single month devoted by these "exact skull measurers" to
the study of Gegenbaur's theory of the skull, and to testing the
hypothesis by the skulls of Selachians, would have yielded them more
fruit and have given them more light than long years of describing and
measuring human skulls, however various.
Virchow himself affords the most striking example of the usual results
of this so-called "exact method" of studying skulls. In his popular
essay on "The Skulls of Men and Apes," 1870, he concludes with this
notable proposition:--"It is therefore self-evident that Man can never
by any progressive development have originated from the Apes." Every
evolutionist who is familiar with the surprising facts of comparative
morphology will draw from them the opposite conclusion: "It is
self-evident that Man could only have originated from the progressive
development of the Ape (organism)."
This brings us to that question which, in the popular treatment of the
theory of descent, is justly considered as its most important outcome
and as the keystone of the evolutionist edifice--to the well-known
proposition, "Man is descended from the Ape." While we simply ignore
all the misrepresentation, distortion, and misinterpretation which
this ape, or pithecoid hypothesis, has met with on all sides, we will
only remark that this fundamental proposition, in the sense of our
modern doctrine of evolution, can rationally have only this plain
meaning: that the human species as a whole was long since developed
from the order of apes, indeed actually from one (or perhaps more)
long since extinct form of ape; the immediate progenitors of man in
the long series of his vertebrate ancestry were apes or ape-like
animals. Of course none of the now surviving species of apes is to be
regarded as the unaltered posterity of that primeval parent-form.
Virchow, however, understanding the "ape question" in this sense,
answers it, as Bastian also does, with the most positive
contradiction. "We cannot teach the doctrine that man is descended
from apes or from any other animal, for we cannot regard it as a real
acquisition of science" (p. 31). Although I myself, in direct
opposition to this view, and in agreement with almost all my
professional colleagues, look upon the descent of man from apes as one
of the surest of phylogenetic hypotheses, I will here expressly admit
that the _relative_ certainty of this, as of all other historical
hypotheses of descent, is not comparable with the _absolute_ certainty
of the general theory of descent. It is now ten years since I first
explicitly stated (in my "Natural History of Creation," vol. ii. p.
358): "The pedigree of the human race, like that of every animal or
plant, remains in detail a more or less approximate general
hypothesis. This, however, in no way affects the application of the
theory of descent to man. In this, as in all researches into the
derivation of our organism, we must distinguish between the _general
theory_ of descent and the _specific hypothesis_ of descent. The
general theory of descent claims full and permanent value, because it
is inductively based on the whole range of common biological phenomena
and on their internal causal connection. Each special hypothesis of
descent, on the other hand, is conditional as to its specific value on
the existing state of our biological information, and on the extent of
those objective empirical grounds on which we deductively found the
hypothesis, by our subjective inferences." And I must here
emphatically add that I have on every opportunity repeated that
reservation, and have always insisted on the difference which exists
between the absolute certainty of transmutation in general and the
relative certainty of each individual specific pedigree. So that when
Semper and others of my opponents assert that I teach my specific
genealogies as "infallible dogmas," it is simply false. I have, on the
contrary, pointed out on all occasions that I regard them only as
_heuristic or provisional hypotheses_, and as a means of investigating
the actual relations of cognate races of organic forms more and more
approximately.
Since the conception of the natural animal system as a hypothetical
genealogical tree, and the phylogenetic interpretation of
morphological affinity which that conception involves, afford in fact
the only rational interpretation of that affinity in general, my first
genealogical attempts soon found many imitators, and at the present
time numerous industrious labourers in the different departments of
systematic zoology are endeavouring to find in the construction of
such hypothetical genealogies the shortest and completest expression
of the modern conception of structural affinity. If Virchow had not
been as ignorant of the true significance and method of systematic
morphology as he is of its progress and scientific contents, he must
certainly have known this, and then he would surely have withheld his
mockery of all these grave phylogenetic studies as "personal
crotchets" and worthless dreams.
What mighty strides towards a mechanical morphology we have made by
this phylogenetic working out of the system, and how much light and
life it has at once thrown into the system that before was dead and
cold, can only be known to those who have long and deeply studied
specific systematisation and the grouping of species; Virchow has not
the remotest suspicion of it. Moreover, these attempts have now
proceeded so far, that a large proportion of the phylogenetic
hypotheses are regarded as very nearly certain, and can hardly
undergo any further essential modifications; while the greater number
of them are still in an unfixed state, and one systematist tries to
improve them in this direction, and another in that.
The following phylogenetic hypotheses are held to be almost
certain:----The descent of many-celled animals from single-celled, of
the Medusae from the hydroid Polyps, of the jointed from the unjointed
worms, of the sucking from the gnawing insects, of amphibious animals
from fishes, of birds from reptiles, of the placental mammalia from
the marsupials, and so forth. I personally consider the descent of man
from the apes as equally certain; nay, I regard this most important
and pregnant genealogical hypothesis as one of those which, up to the
present time, rest on the best empirical basis.
Huxley, in particular, fifteen years ago, in his celebrated "Man's
Place in Nature," 1863, so admirably proved the undoubted "descent of
man from apes," and so clearly discussed all the relations that had to
be taken into consideration, that very little was left to others to
do. The result of his comparative morphological investigations is
contained in this proposition----" If we take up a system of organs,
be it which we will, the comparison of its modifications throughout
the series of apes leads us to the same conclusion: that in every
single visible character man differs less from the higher apes than
these do from the lower members of the same order." It is therefore
impossible for any objective zoologist, according to the principles of
comparative systematisation, to ascribe to man any other place in the
animal world than in the order of apes; and it is quite immaterial
whether we designate this individual group as the Order of Apes, or,
with Linnaeus, as the Primates. For the phylogenetic construction of
the system, the common descent of man and of apes from one common
parent-form, necessarily follows from this inevitable grouping,
and on this proposition only all the general inferences of the
"ape-hypothesis" depend. As to what that common parent-form of men and
apes may have been, very different views might probably be brought on
opposite sides; but any one who knows the collected facts that bear
upon the matter, and estimates them impartially, must, in conclusion,
arrive at the certain conviction that that hypothetical and long-since
extinct parent-form can only have been genuine apes; that is to say,
of the placental mammalian type, such as when we see them now living
before our eyes we unhesitatingly class, on the ground of their
zoological characters, as true apes, in the order of Apes or Primates.
In this, and all other sound phylogenetic hypotheses, we may most
easily attain to a conviction of their truth by taking into
consideration and comparison the other possible hypotheses. But in
fact no single opponent of the ape-hypothesis has been able to combat
it with any other phylogenetic hypothesis that has the faintest
glimmer of probability. Not one opponent has suggested, or can
suggest, any other animal form that can serve as our nearest ancestor
than the ape. No one has ever reproached me by saying that Mother
Nature has endowed me with too little imagination; on the contrary, I
am often accused of having a superfluity of that gift of the gods; but
I have often and repeatedly exerted my imagination to picture to
myself any known or unknown animal-form as the nearest parent-form to
man in the place of the apes, and have always found myself under the
necessity of falling back upon the stock of apes. Let me conceive of
the outward conformation and the internal structure of the nearest
mammalian ancestors of men as I will, I am always forced to
acknowledge that this hypothetical parent-form ranges under the
zoologically-conceived order of apes, and cannot possibly be separated
from the Simiadoe or Primates. If, in spite of this, any one chooses,
out of a "personal crotchet," to accept some other series of unknown
animal ancestors of man that have nothing to do with apes, that is but
a mere empty hypothesis floating in the air. Our ape-hypothesis, on
the other hand, is objectively and thoroughly proved by the essential
agreement of the internal bodily structure of man and of apes, and by
the identity of their embryonic development, as I have fully shown in
my "Evolution of Man" (chaps. xix. and xxvi.) The mode and manner in
which he here puts palaeontology in the foreground, and throws on the
theory of descent the task of producing an unbroken gradation of
fossil transitional forms between the apes and man, is very indicative
of Virchow's ignorance of this zoological question--in which I, as a
professional zoologist, must decisively declare his incompetence. The
reasons why such a solution of the problem is not to be expected, the
extraordinary imperfection of the palaeontological record, the natural
impediments to the palaeontological evidence of the genealogical table,
have been so lucidly unfolded by Darwin himself (chaps. ix. and x. of
the "Origin of Species") that I am obliged once more to come to the
conclusion that Virchow has never read it with any attention.
Besides, long before Darwin, the gifted Lyell, the great originator of
modern geology, showed clearly and convincingly how, for many reasons,
the greater part of the fossil series must remain most imperfect, and
these reasons were at a later period so often and so fully discussed
(by myself among others, in chap. xv. of the "History of Creation,"
vol. ii. pp. 24-32) that it is wholly superfluous once more and in
this place to state these well-known and time-worn questions. It only
shows how little Virchow was acquainted with geology and palaeontology,
and what a limited judgment he can form of these historical causal
relations.
FOOTNOTES:
[15] Vol. i. p. 293.