Library: Historical Documents: Charles Darwin: Descent of Man: Chapter 6

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Descent of Man [ 1871 ]

Charles Darwin [ 1809 - 1882 ]

Chapter VI - On the Affinities and Genealogy of Man

EVEN if it be granted that the difference between man and his
nearest allies is as great in corporeal structure as some
naturalists maintain, and although we must grant that the difference
between them is immense in mental power, yet the facts given in the
earlier chapters appear to declare, in the plainest manner, that man
is descended from some lower form, notwithstanding that
connecting-links have not hitherto been discovered.
Man is liable to numerous, slight, and diversified variations, which
are induced by the same general causes, are governed and transmitted
in accordance with the same general laws, as in the lower animals. Man
has multiplied so rapidly, that he has necessarily been exposed to
struggle for existence, and consequently to natural selection. He
has given rise to many races, some of which differ so much from each
other, that they have often been ranked by naturalists as distinct
species. His body is constructed on the same homological plan as
that of other mammals. He passes through the same phases of
embryological development. He retains many rudimentary and useless
structures, which no doubt were once serviceable. Characters
occasionally make their re-appearance in him, which we have reason
to believe were possessed by his early progenitors. If the origin of
man had been wholly different from that of all other animals, these
various appearances would be mere empty deceptions; but such an
admission is incredible. These appearances, on the other hand, are
intelligible, at least to a large extent, if man is the
co-descendant with other mammals of some unknown and lower form.
Some naturalists, from being deeply impressed with the mental and
spiritual powers of man, have divided the whole organic world into
three kingdoms, the Human, the Animal, and the Vegetable, thus
giving to man a separate kingdom.* Spiritual powers cannot be compared
or classed by the naturalist: but he may endeavour to shew, as I
have done, that the mental faculties of man and the lower animals do
not differ in kind, although immensely in degree. A difference in
degree, however great, does not justify us in placing man in a
distinct kingdom, as will perhaps be best illustrated by comparing the
mental powers of two insects, namely, a coccus or scale-insect and
an ant, which undoubtedly belong to the same class. The difference
is here greater than, though of a somewhat different kind from, that
between man and the highest mammal. The female coccus, whilst young,
attaches itself by its proboscis to a plant; sucks the sap, but
never moves again; is fertilised and lays eggs; and this is its
whole history. On the other hand, to describe the habits and mental
powers of worker-ants, would require, as Pierre Huber has shewn, a
large volume; I may, however, briefly specify a few points. Ants
certainly communicate information to each other, and several unite for
the same work, or for games of play. They recognise their
fellow-ants after months of absence, and feel sympathy for each other.
They build great edifices, keep them clean, close the doors in the
evening, and post sentries. They make roads as well as tunnels under
rivers, and temporary bridges over them, by clinging together. They
collect food for the community, and when an object, too large for
entrance, is brought to the nest, they enlarge the door, and
afterwards build it up again. They store up seeds, of which they
prevent the germination, and which, if damp, are brought up to the
surface to dry. They keep aphides and other insects as milch-cows.
They go out to battle in regular bands, and freely sacrifice their
lives for the common weal. They emigrate according to a preconcerted
plan. They capture slaves. They move the eggs of their aphides, as
well as their own eggs and cocoons, into warm parts of the nest, in
order that they may be quickly hatched; and endless similar facts
could be given.*(2) On the whole, the difference in mental power
between an ant and a coccus is immense; yet no one has ever dreamed of
placing these insects in distinct classes, much less in distinct
kingdoms. No doubt the difference is bridged over by other insects;
and this is not the case with man and the higher apes. But we have
every reason to believe that the breaks in the series are simply the
results of many forms having become extinct.

* Isidore Geoffroy St-Hilaire gives a detailed account of the
position assigned to man by various naturalists in their
classifications: Hist. Nat. Gen. tom. ii., 1859, pp. 170-189.
*(2) Some of the most interesting facts ever published on the habits
of ants are given by Mr. Belt, in his The Naturalist in Nicaragua,
1874. See also Mr. Moggridge's admirable work, Harvesting Ants, &c.,
1873, also "L'Instinct chez les insectes," by M. George Pouchet, Revue
des Deux Mondes, Feb., 1870, p. 682.

Professor Owen, relying chiefly on the structure of the brain, has
divided the mammalian series into four sub-classes. One of these he
devotes to man; in another he places both the marsupials and the
Monotremata; so that he makes man as distinct from all other mammals
as are these two latter groups conjoined. This view has not been
accepted, as far as I am aware, by any naturalist capable of forming
an independent judgment, and therefore need not here be further
considered.
We can understand why a classification founded on any single
character or organ- even an organ so wonderfully complex and important
as the brain- or on the high development of the mental faculties, is
almost sure to prove unsatisfactory. This principle has indeed been
tried with hymenopterous insects; but when thus classed by their
habits or instincts, the arrangement proved thoroughly artificial.*
Classifications may, of course, be based on any character whatever, as
on size, colour, or the element inhabited; but naturalists have long
felt a profound conviction that there is a natural system. This
system, it is now generally admitted, must be, as far as possible,
genealogical in arrangement,- that is, the co-descendants of the
same form must be kept together in one group, apart from the
co-descendants of any other form; but if the parent-forms are related,
so will be their descendants, and the two groups together will form
a larger group. The amount of difference between the several groups-
that is the amount of modification which each has undergone- is
expressed by such terms as genera, families, orders, and classes. As
we have no record of the lines of descent, the pedigree can be
discovered only by observing the degrees of resemblance between the
beings which are to be classed. For this object numerous points of
resemblance are of much more importance than the amount of
similarity or dissimilarity in a few points. If two languages were
found to resemble each other in a multitude of words and points of
construction, they would be universally recognised as having sprung
from a common source, notwithstanding that they differed greatly in
some few words or points of construction. But with organic beings
the points of resemblance must not consist of adaptations to similar
habits of life: two animals may, for instance, have had their whole
frames modified for living in the water, and yet they will not be
brought any nearer to each other in the natural system. Hence we can
see how it is that resemblances in several unimportant structures,
in useless and rudimentary organs, or not now functionally active,
or in an embryological condition, are by far the most serviceable
for classification; for they can hardly be due to adaptations within a
late period; and thus they reveal the old lines of descent or of
true affinity.

* Westwood, Modern Classification of Insects, vol. ii., 1840, p. 87.

We can further see why a great amount of modification in some one
character ought not to lead us to separate widely any two organisms. A
part which already differs much from the same part in other allied
forms has already, according to the theory of evolution, varied
much; consequently it would (as long as the organism remained
exposed to the same exciting conditions) be liable to further
variations of the same kind; and these, if beneficial, would be
preserved, and thus be continually augmented. In many cases the
continued development of a part, for instance, of the beak of a
bird, or of the teeth of a mammal, would not aid the species in
gaining its food, or for any other object; but with man we can see
no definite limit to the continued development of the brain and mental
faculties, as far as advantage is concerned. Therefore in
determining the position of man in the natural or genealogical system,
the extreme development of his brain ought not to outweigh a multitude
of resemblances in other less important or quite unimportant points.
The greater number of naturalists who have taken into
consideration the whole structure of man, including his mental
faculties, have followed Blumenbach and Cuvier, and have placed man in
a separate Order, under the title of the Bimana, and therefore on an
equality with the orders of the Quadrumana, Carnivora, &c. Recently
many of our best naturalists have recurred to the view first
propounded by Linnaeus, so remarkable for his sagacity, and have
placed man in the same Order with the Quadrumana, under the title of
the primates. The justice of this conclusion will be admitted: for
in the first place, we must bear in mind the comparative
insignificance for classification of the great development of the
brain in man, and that the strongly-marked differences between the
skulls of man and the Quadrumana (lately insisted upon by Bischoff,
Aeby, and others) apparently follow from their differently developed
brains. In the second place, we must remember that nearly all the
other and more important differences between man and the Quadrumana
are manifestly adaptive in their nature, and relate chiefly to the
erect position of man; such as the structure of his hand, foot, and
pelvis, the curvature of his spine, and the position of his head.
The family of seals offers a good illustration of the small importance
of adaptive characters for classification. These animals differ from
all other Carnivora in the form of their bodies and in the structure
of their limbs, far more than does man from the higher apes; yet in
most systems, from that of Cuvier to the most recent one by Mr.
Flower,* seals are ranked as a mere family in the Order of the
Carnivora. If man had not been his own classifier, he would never have
thought of founding a separate order for his own reception.

* Proceedings Zoological Society, 1863, p. 4.

It would be beyond my limits, and quite beyond my knowledge, even to
name the innumerable points of structure in which man agrees with
the other primates. Our great anatomist and philosopher, Prof. Huxley,
has fully discussed this subject,* and concludes that man in all parts
of his organization differs less from the higher apes, than these do
from the lower members of the same group. Consequently there "is no
justification for placing man in a distinct order."

* Evidence as to Man's Place in Nature, 1863, p. 70, et passim

In an early part of this work I brought forward various facts,
shewing how closely man agrees in constitution with the higher
mammals; and this agreement must depend on our close similarity in
minute structure and chemical composition. I gave, as instances, our
liability to the same diseases, and to the attacks of allied
parasites; our tastes in common for the same stimulants, and the
similar effects produced by them, as well as by various drugs, and
other such facts.
As small unimportant points of resemblance between man and the
Quadrumana are not commonly noticed in systematic works, and as,
when numerous, they clearly reveal our relationship, I will specify
a few such points. The relative position of our features is manifestly
the same; and the various emotions are displayed by nearly similar,
movements of the muscles and skin, chiefly above the eyebrows and
round the mouth. Some few expressions are, indeed, almost the same, as
in the weeping of certain kinds of monkeys and in the laughing noise
made by others, during which the corners of the mouth are drawn
backwards, and the lower eyelids wrinkled. The external ears are
curiously alike. In man the nose is much more prominent than in most
monkeys; but we may trace the commencement of an aquiline curvature in
the nose of the Hoolock gibbon; and this in the Semnopithecus nasica
is carried to a ridiculous extreme.
The faces of many monkeys are ornamented with beards, whiskers, or
moustaches. The hair on the head grows to a great length in some
species of Semnopithecus;* and in the bonnet monkey (Macacus radiatus)
it radiates from a point on the crown, with a parting down the middle.
It is commonly said that the forehead gives to man his noble and
intellectual appearance; but the thick hair on the head of the
bonnet monkey terminates downwards abruptly, and is succeeded by
hair so short and fine that at a little distance the forehead, with
the exception of the eyebrows, appears quite naked. It has been
erroneously asserted that eyebrows are not present in any monkey. In
the species just named the degree of nakedness of the forehead differs
in different individuals; and Eschricht states*(2) that in our
children the limit between the hairy scalp and the naked forehead is
sometimes not well defined; so that here we seem to have a trifling
case of reversion to a progenitor, in whom the forehead had not as yet
become quite naked.

* Isidore Geoffroy St-Hilaire, Hist. Nat. Gen., tom. ii., 1859, p.
217.
*(2) "Uber die Richtung der Haare, &c.," Muller's Archiv fur Anat.
und Phys., 1837, s. 51.

It is well known that the hair on our arms tends to converge from
above and below to a point at the elbow. This curious arrangement,
so unlike that in most of the lower mammals, is common to the gorilla,
chimpanzee, orang, some species of Hylobates, and even to some few
American monkeys. But in Hylobates agilis the hair on the forearm is
directed downwards or towards the wrist in the ordinary manner; and in
H. lar it is nearly erect, with only a very slight forward
inclination; so that in this latter species it is in a transitional
state. It can hardly be doubted that with most mammals the thickness
of the hair on the back and its direction, is adapted to throw off the
rain; even the transverse hairs on the fore-legs of a dog may serve
for this end when he is coiled up asleep. Mr. Wallace, who has
carefully studied the habits of the orang, remarks that the
convergence of the hair towards the elbow on the arms of the orang may
be explained as serving to throw off the rain, for this animal
during rainy weather sits with its arms bent, and with the hands
clasped round a branch or over its head. According to Livingstone, the
gorilla also "sits in pelting rain with his hands over his head."*
If the above explanation is correct, as seems probable, the
direction of the hair on our own arms offers a curious record of our
former state; for no one supposes that it is now of any use in
throwing off the rain; nor, in our present erect condition, is it
properly directed for this purpose.

* Quoted by Reade, African Sketch Book, vol i., 1873, p. 152.

It would, however, be rash to trust too much to the principle of
adaptation in regard to the direction of the hair in man or his
early progenitors; for it is impossible to study the figures given
by Eschricht of the arrangement of the hair on the human foetus
(this being the same as in the adult) and not agree with this
excellent observer that other and more complex causes have intervened.
The points of convergence seem to stand in some relation to those
points in the embryo which are last closed in during development.
There appears, also, to exist some relation between the arrangement of
the hair on the limbs, and the course of the medullary arteries.*

* On the hair in Hylobates, see Natural History of Mammals, by C. L.
Martin, 1841, p. 415. Also, Isidore Geoffroy on the American monkeys
and other kinds, Hist. Nat. Gen., vol. ii., 1859, pp. 216, 243.
Eschricht, ibid., ss. 46, 55, 61. Owen, Anatomy of Vertebrates, vol.
iii., p. 619. Wallace, Contributions to the Theory of Natural
Selection, 1870, p. 344.

It must not be supposed that the resemblances between man and
certain apes in the above and in many other points- such as in
having a naked forehead, long tresses on the head, &c.,- are all
necessarily the result of unbroken inheritance from a common
progenitor, or of subsequent reversion. Many of these resemblances are
more probably due to analogous variation, which follows, as I have
elsewhere attempted to shew,* from co-descended organisms having a
similar constitution, and having been acted on by like causes inducing
similar modifications. With respect to the similar direction of the
hair on the fore-arms of man and certain monkeys, as this character is
common to almost all the anthropomorphous apes, it may probably be
attributed to inheritance; but this is not certain, as some very
distinct American monkeys are thus characterised.

* Origin of Species. The Variation of Animals and Plants under
Domestication, vol. ii., 1868, p. 348.

Although, as we have now seen, man has no just right to form a
separate Order for his own reception, he may perhaps claim a
distinct sub-order or family. Prof. Huxley, in his last work,* divides
the primates into three suborders; namely, the Anthropidae with man
alone, the Simiadae including monkeys of all kinds, and the
Lemuridae with the diversified genera of lemurs. As far as differences
in certain important points of structure are concerned, man may no
doubt rightly claim the rank of a sub-order; and this rank is too low,
if we look chiefly to his mental faculties. Nevertheless, from a
genealogical point of view it appears that this rank is too high,
and that man ought to form merely a family, or possibly even only a
sub-family. If we imagine three lines of descent proceeding from a
common stock, it is quite conceivable that two of them might after the
lapse of ages be so slightly changed as still to remain as species
of the same genus, whilst the third line might become so greatly
modified as to deserve to rank as a distinct sub-family, or even
Order. But in this case it is almost certain that the third line would
still retain through inheritance numerous small points of
resemblance with the other two. Here, then, would occur the
difficulty, at present insoluble, how much weight we ought to assign
in our classifications to strongly-marked differences in some few
points,- that is, to the amount of modification undergone; and how
much to close resemblance in numerous unimportant points, as
indicating the lines of descent or genealogy. To attach much weight to
the few but strong differences is the most obvious and perhaps the
safest course, though it appears more correct to pay great attention
to the many small resemblances, as giving a truly natural
classification.

* An Introduction to the Classification of Animals, 1869, p. 99.

In forming a judgment on this head with reference to man, we must
glance at the classification of the Simiadae. This family is divided
by almost all naturalists into the catarhine group, or Old World
monkeys, all of which are characterised (as their name expresses) by
the peculiar structure of their nostrils, and by having four premolars
in each jaw; and into the platyrhine group or New World monkeys
(including two very distinct sub-groups), all of which are
characterised by differently constructed nostrils, and by having six
premolars in each jaw. Some other small differences might be
mentioned. Now man unquestionably belongs in his dentition, in the
structure of his nostrils, and some other respects, to the catarhine
or Old World division; nor does he resemble the platyrhines more
closely than the catarhines in any characters, excepting in a few of
not much importance and apparently of an adaptive nature. It is
therefore against all probability that some New World species should
have formerly varied and produced a man-like creature, with all the
distinctive characters proper to the Old World division; losing at the
same time all its own distinctive characters. There can, consequently,
hardly be a doubt that man is an off-shoot from the Old World simian
stem; and that under a genealogical point of view he must be classed
with the catarhine division.*

* This is nearly the same classification as that provisionally
adopted by Mr. St. G. Mivart, Transactions, Philosophical Society,
1867, p. 300, who, after separating the Lemuridae, divides the
remainder of the Primates into the Hominidae, the Simiadae which
answer to the catarhines, the Cebidae, and the Hapalidae,- these two
latter groups answering to the platyrhines. Mr. Mivart still abides by
the same view; see Nature, 1871, p. 481.

The anthropomorphous apes, namely the gorilla, chimpanzee, orang,
and Hylobates, are by most naturalists separated from the other Old
World monkeys, as a distinct sub-group. I am aware that Gratiolet,
relying on the structure of the brain, does not admit the existence of
this sub-group, and no doubt it is a broken one. Thus the orang, as
Mr. St. G. Mivart remarks, "is one of the most peculiar and aberrant
forms to be found in the Order."* The remaining non-anthropomorphous
Old World monkeys, are again divided by some naturalists into two or
three smaller subgroups; the genus Semnopithecus, with its peculiar
sacculated stomach, being the type of one sub-group. But it appears
from M. Gaudry's wonderful discoveries in Attica, that during the
Miocene period a form existed there, which connected Semnopithecus and
Macacus; and this probably illustrates the manner in which the other
and higher groups were once blended together.

* Transactions, Zoolog. Soc., vol. vi., 1867, p. 214.

If the anthropomorphous apes be admitted to form a natural
sub-group, then as man agrees with them, not only in all those
characters which he possesses in common with the whole catarhine
group, but in other peculiar characters, such as the absence of a tail
and of callosities, and in general appearance, we may infer that
some ancient member of the anthropomorphous sub-group gave birth to
man. It is not probable that, through the law of analogous
variation, a member of one of the other lower sub-groups should have
given rise to a man-like creature, resembling the higher
anthropomorphous apes in so many respects. No doubt man, in comparison
with most of his allies, has undergone an extraordinary amount of
modification, chiefly in consequence of the great development of his
brain and his erect position; nevertheless, we should bear in mind
that he "is but one of several exceptional forms of primates."*

* Mr. St. G. Mivart, Transactions of the Philosophical Society,
1867, p. 410.

Every naturalist, who believes in the principle of evolution, will
grant that the two main divisions of the Simiadae, namely the
catarhine and platyrhine monkeys, with their sub-groups, have all
proceeded from some one extremely ancient progenitor. The early
descendants of this progenitor, before they had diverged to any
considerable extent from each other, would still have formed a
single natural group; but some of the species or incipient genera
would have already begun to indicate by their diverging characters the
future distinctive marks of the catarhine and platyrhine divisions.
Hence the members of this supposed ancient group would not have been
so uniform in their dentition, or in the structure of their
nostrils, as are the existing catarhine monkeys in one way and the
platyrhines in another way, but would have resembled in this respect
the allied Lemuridae, which differ greatly from each other in the form
of their muzzles,* and to an extraordinary degree in their dentition.

* Messrs. Murie and Mivart on the Lemuroidea, Transactions,
Zoological Society, vol. vii, 1869, p. 5.

The catarhine and platyrhine monkeys agree in a multitude of
characters, as is shewn by their unquestionably belonging to one and
the same Order. The many characters which they possess in common can
hardly have been independently acquired by so many distinct species;
so that these characters must have been inherited. But a naturalist
would undoubtedly have ranked as an ape or a monkey, an ancient form
which possessed many characters common to the catarhine and platyrhine
monkeys, other characters in an intermediate condition, and some
few, perhaps, distinct from those now found in either group. And as
man from a genealogical point of view belongs to the catarhine or
Old World stock, we must conclude, however much the conclusion may
revolt our pride, that our early progenitors would have been
properly thus designated.* But we must not fall into the error of
supposing that the early progenitors of the whole simian stock,
including man, was identical with, or even closely resembled, any
existing ape or monkey.

* Haeckel has come to this same conclusion. See "Uber die Entstehung
des Menschengeschlechts," in Virchow's Sammlung. gemein. wissen.
Vortrage, 1868, s. 61. Also his Naturliche Schopfungsgeschicte,
1868, in which he gives in detail his views on the genealogy of man.

On the Birthplace and Antiquity of Man.- We are naturally led to
enquire, where was the birthplace of man at that stage of descent when
our progenitors diverged from the catarhine stock? The fact that
they belonged to the stock clearly shews that they inhabited the Old
World; but not Australia nor any oceanic island, as we may infer
from the laws of geographical distribution. In each great region of
the world the living mammals are closely related to the extinct
species of the same region. It is therefore probable that Africa was
formerly inhabited by extinct apes closely allied to the gorilla and
chimpanzee; and as these two species are now man's nearest allies,
it is somewhat more probable that our early progenitors lived on the
African continent than elsewhere. But it is useless to speculate on
this subject; for two or three anthropomorphous apes, one the
Dryopithecus* of Lartet, nearly as large as a man, and closely
allied to Hylobates, existed in Europe during the Miocene age; and
since so remote a period the earth has certainly undergone many
great revolutions, and there has been ample time for migration on
the largest scale.

* Dr. C Forsyth Major, "Sur les Singes fossiles trouves en
Italie," Soc. Ital. des Sc. Nat., tom., xv., 1872.

At the period and place, whenever and wherever it was, when man
first lost his hairy covering, he probably inhabited a hot country;
a circumstance favourable for the frugi-ferous diet on which,
judging from analogy, he subsisted. We are far from knowing how long
ago it was when man first diverged from the catarhine stock; but it
may have occurred at an epoch as remote as the Eocene period; for that
the higher apes had diverged from the lower apes as early as the Upper
Miocene period is shewn by the existence of the Dryopithecus. We are
also quite ignorant at how rapid a rate organisms, whether high or low
in the scale, may be modified under favourable circumstances; we know,
however, that some have retained the same form during an enormous
lapse of time. From what we see going on under domestication, we learn
that some of the co-descendants of the same species may be not at all,
some a little, and some greatly changed, all within the same period.
Thus it may have been with man, who has undergone a great amount of
modification in certain characters in comparison with the higher apes.
The great break in the organic chain between man and his nearest
allies, which cannot be bridged over by any extinct or living species,
has often been advanced as a grave objection to the belief that man is
descended from some lower form; but this objection will not appear
of much weight to those who, from general reasons, believe in the
general principle of evolution. Breaks often occur in all parts of the
series, some being wide, sharp and defined, others less so in
various degrees; as between the orang and its nearest allies-
between the Tarsius and the other Lemuridae- between the elephant, and
in a more striking manner between the Ornithorhynchus or Echidna,
and all other mammals. But these breaks depend merely on the number of
related forms which have become extinct. At some future period, not
very distant as measured by centuries, the civilised races of man will
almost certainly exterminate, and replace, the savage races throughout
the world. At the same time the anthropomorphous apes, as Professor
Schaaffhausen has remarked,* will no doubt be exterminated. The
break between man and his nearest allies will then be wider, for it
will intervene between man in a more civilised state, as we may
hope, even than the Caucasian, and some ape as low as a baboon,
instead of as now between the negro or Australian and the gorilla.

* Anthropological Review, April, 1867, p. 236

With respect to the absence of fossil remains, serving to connect
man with his ape-like progenitors, no one will lay much stress on this
fact who reads Sir C. Lyell's discussion,* where he shews that in
all the vertebrate classes the discovery of fossil remains has been
a very slow and fortuitous process. Nor should it be forgotten that
those regions which are the most likely to afford remains connecting
man with some extinct ape-like creature, have not as yet been searched
by geologists.

* Elements of Geology, 1865, pp. 583-585. Antiquity of Man, 1863, p.
145.

Lower Stages in the Genealogy of Man.- We have seen that man appears
to have diverged from the catarhine or Old World division of the
Simiadae, after these had diverged from the New World division. We
will now endeavour to follow the remote traces of his genealogy,
trusting principally to the mutual affinities between the various
classes and orders, with some slight reference to the periods, as
far as ascertained, of their successive appearance on the earth. The
Lemuridae stand below and near to the Simiadae, and constitute a
very distinct family of the primates, or, according to Haeckel and
others, a distinct Order. This group is diversified and broken to an
extraordinary degree, and includes many aberrant forms. It has,
therefore, probably suffered much extinction. Most of the remnants
survive on islands, such as Madagascar and the Malayan archipelago,
where they have not been exposed to so severe a competition as they
would have been on well-stocked continents. This group likewise
presents many gradations, leading, as Huxley remarks,* "insensibly
from the crown and summit of the animal creation down to creatures
from which there is but a step, as it seems, to the lowest,
smallest, and least intelligent of the placental mammalia." From these
various considerations it is probable that the Simiadae were
originally developed from the progenitors of the existing Lemuridae;
and these in their turn from forms standing very low in the
mammalian series.

* Man's Place in Nature, p. 105.

The marsupials stand in many important characters below the
placental mammals. They appeared at an earlier geological period,
and their range was formerly much more extensive than at present.
Hence the Placentata are generally supposed to have been derived
from the Implacentata or marsupials; not, however, from forms
closely resembling the existing marsupials, but from their early
progenitors. The Monotremata are plainly allied to the marsupials,
forming a third and still lower division in the great mammalian
series. They are represented at the present day solely by the
Ornithorhynchus and Echidna; and these two forms may be safely
considered as relics of a much larger group, representatives of
which have been preserved in Australia through some favourable
concurrence of circumstances. The Monotremata are eminently
interesting, as leading in several important points of structure
towards the class of reptiles.
In attempting to trace the genealogy of the Mammalia, and
therefore of man, lower down in the series, we become involved in
greater and greater obscurity; but as a most capable judge, Mr.
Parker, has remarked, we have good reason to believe, that no true
bird or reptile intervenes in the direct line of descent. He who
wishes to see what ingenuity and knowledge can effect, may consult
Prof. Haeckel's works.* I will content myself with a few general
remarks. Every evolutionist will admit that the five great
vertebrate classes, namely, mammals, birds, reptiles, amphibians,
and fishes, are descended from some one prototype; for they have
much in common, especially during their embryonic state. As the
class of fishes is the most lowly organised, and appeared before the
others, we may conclude that all the members of the vertebrate kingdom
are derived from some fishlike animal. The belief that animals so
distinct as a monkey, an elephant, a humming-bird, a snake, a frog,
and a fish, &c., could all have sprung from the same parents, will
appear monstrous to those who have not attended to the recent progress
of natural history. For this belief implies the former existence of
links binding closely together all these forms, now so utterly unlike.

* Elaborate tables are given in his Generelle Morphologie (B. ii.,
s. cliii. and s. 425); and with more especial reference to man in
his Naturliche Schopfungsgeschichte, 1868. Prof. Huxley, in
reviewing this latter work (The Academy, 1869, p. 42), says that he
considers the phylum or lines of descent of the Vertebrata to be
admirably discussed by Haeckel, although he differs on some points. He
expresses, also, his high estimate of the general tenor and spirit
of the whole work.

Nevertheless, it is certain that groups of animals have existed,
or do now exist, which serve to connect several of the great
vertebrate classes more or less closely. We have seen that the
Ornithorhynchus graduates towards reptiles; and Prof. Huxley has
discovered, and is confirmed by Mr. Cope and others, that the
dinosaurians are in many important characters intermediate between
certain reptiles and certain birds- the birds referred to being the
ostrich-tribe (itself a widely-diffused remnant of a larger group) and
the Archeopteryx, that strange secondary bird, with a long lizard-like
tail. Again, according to Prof. Owen,* the ichthyosaurians- great
sea-lizards furnished with paddles- present many affinities with
fishes, or rather, according to Huxley, with amphibians; a class
which, including in its highest division frogs and toads, is plainly
allied to the ganoid fishes. These latter fishes swarmed during the
earlier geological periods, and were constructed on what is called a
generalised type, that is, they presented diversified affinities
with other groups of organisms. The Lepidosiren is also so closely
allied to amphibians and fishes, that naturalists long disputed in
which of these two classes to rank it; it, and also some few ganoid
fishes, have been preserved from utter extinction by inhabiting
rivers, which are harbours of refuge, and are related to the great
waters of the ocean in the same way that islands are to continents.

* Palaeontology 1860, p. 199.

Lastly, one single member of the immense and diversified class of
fishes, namely, the lancelet or amphioxus, is so different from all
other fishes, that Haeckel maintains that it ought to form a
distinct class in the vertebrate kingdom. This fish is remarkable
for its negative characters; it can hardly be said to possess a brain,
vertebral column, or heart, &c.; so that it was classed by the older
naturalists amongst the worms. Many years ago Prof. Good sir perceived
that the lancelet presented some affinities with the ascidians,
which are invertebrate, hermaphrodite, marine creatures permanently
attached to a support. They hardly appear like animals, and consist of
a simple, tough, leathery sack, with two small projecting orifices.
They belong to the Mulluscoida of Huxley- a lower division of the
great kingdom of the Mollusca; but they have recently been placed by
some naturalists amongst the Vermes or worms. Their larvae somewhat
resemble tadpoles in shape,* and have the power of swimming freely
about. Mr. Kovalevsky*(2) has lately observed that the larvae of
ascidians are related to the Vertebrata, in their manner of
development, in the relative position of the nervous system, and in
possessing a structure closely like the chorda dorsalis of
vertebrate animals; and in this he has been since confirmed by Prof.
Kupffer. M. Kovalevsky writes to me from Naples, that he has now
carried these observations yet further, and should his results be well
established, the whole will form a discovery of the very greatest
value. Thus, if we may rely on embryology, ever safest guide in
classification, it seems that we have at last gained a clue to the
source whence the Vertebrata were derived.*(3) We should then be
justified in believing that at an extremely remote period a group of
animals existed, resembling in many respects the larvae of our present
ascidians, which diverged into two great branches- the one
retrograding in development and producing the present class of
ascidians, the other rising to the crown and summit of the animal
kingdom by giving birth to the Vertebrata.

* At the Falkland Islands I had the satisfaction of seeing, in
April, 1833, and therefore some years before any other naturalist, the
locomotive larvae of a compound ascidian, closely allied to
Synoicum, but apparently generically distinct from it. The tail was
about five times as long as the oblong head, and terminated in a
very fine filament. It was, as sketched by me under a simple
microscope, plainly divided by transverse opaque partitions, which I
presume represent the great cells figured by Kovalevsky. At an early
stage of development the tail was closely coiled round the head of the
larva.
*(2) Memoires de l'Acad. des Sciences de St. Petersbourg, tom. x.,
No. 15, 1866.
*(3) But I am bound to add that some competent judges dispute this
conclusion; for instance, M. Giard, in a series of papers in the
Archives de Zoologie Experimentale, for 1872. Nevertheless, this
naturalist remarks, p. 281, "L'organisation de la larve ascidienne
en dehors de toute hypothese et de toute theorie, nous montre
comment la nature peut produire la disposition fondamentale du type
vertebre (l'existence d'une corde dorsale) chez un invertebre par la
seule condition vitale de l'adaptation, et cette simple possibilite du
passage supprime l'abime entre les deux sous-regnes, encore bien qu'en
ignore par ou le passage sest fait en realite."

We have thus far endeavoured rudely to trace the genealogy of the
Vertebrata by the aid of their mutual affinities. We will now look
to man as he exists; and we shall, I think, be able partially to
restore the structure of our early progenitors, during successive
periods, but not in due order of time. This, can be effected by
means of the rudiments which man still retains, by the characters
which occasionally make their appearance in him through reversion, and
by the aid of the principles of morphology and embryology. The variousfacts, to which I shall here allude, have been given in the previous
chapters.
The early progenitors of man must have been once covered with
hair, both sexes having beards; their ears were probably pointed,
and capable of movement; and their bodies were provided with a tail,
having the proper muscles. Their limbs and bodies were also acted on
by many muscles which now only occasionally reappear, but are normally
present in the Quadrumana. At this or some earlier period, the great
artery and nerve of the humerus ran through a supra-condyloid foramen.
The intestine gave forth a much larger diverticulum or caecum than
that now existing. The foot was then prehensile, judging from the
condition of the great toe in the foetus; and our progenitors, no
doubt, were arboreal in their habits, and frequented some warm,
forest-clad land. The males had great canine teeth, which served
them as formidable weapons. At a much earlier period the uterus was
double; the excreta were voided through a cloaca; and the eye was
protected by a third eyelid or nictitating membrane. At a still
earlier period the progenitors of man must have been aquatic in
their habits; for morphology plainly tells us that our lungs consist
of a modified swimbladder, which once served as a float. The clefts on
the neck in the embryo of man show where the branchiae once existed.
In the lunar or weekly recurrent periods of some of our functions we
apparently still retain traces of our primordial birthplace, a shore
washed by the tides. At about this same early period the true
kidneys were replaced by the corpora wolffiana. The heart existed as a
simple pulsating vessel; and the chorda dorsalis took the place of a
vertebral column. These early ancestors of man, thus seen in the dim
recesses of time, must have been as simply, or even still more
simply organised than the lancelet or amphioxus.
There is one other point deserving a fuller notice. It has long been
known that in the vertebrate kingdom one sex bears rudiments of
various accessory parts, appertaining to the reproductive system,
which properly belong to the opposite sex; and it has now been
ascertained that at a very early embryonic period both sexes possess
true male and female glands. Hence some remote progenitor of the whole
vertebrate kingdom appears to have been hermaphrodite or androgynous.*
But here we encounter a singular difficulty. In the mammalian class
the males possess rudiments of a uterus with the adjacent passage,
in their vesiculae prostaticae; they bear also rudiments of mammae,
and some male marsupials have traces of a marsupial sack.*(2) Other
analogous facts could be added. Are we, then, to suppose that some
extremely ancient mammal continued androgynous, after it had
acquired the chief distinctions of its class, and therefore after it
had diverged from the lower classes of the vertebrate kingdom? This
seems very improbable, for we have to look to fishes, the lowest of
all the classes, to find any still existent androgynous forms.*(3)
That various accessory parts, proper to each sex, are found in a
rudimentary condition in the opposite sex, may be explained by such
organs having been gradually acquired by the one sex, and then
transmitted in a more or less imperfect state to the other. When we
treat of sexual selection, we shall meet with innumerable instances of
this form of transmission,- as in the case of the spurs, plumes, and
brilliant colours, acquired for battle or ornament by male birds,
and inherited by the females in an imperfect or rudimentary condition.

* This is the conclusion of Prof. Gegenbaur, one of the highest
authorities in comparative anatomy: see Grundzuge der vergleich.
Anat., 1870, s. 876. The result has been arrived at chiefly from the
study of the Amphibia; but it appears from the researches of
Waldeyer (as quoted in Journal of Anat. and Phys., 1869, p. 161), that
the sexual organs of even "the higher vertebrata are, in their early
condition, hermaphrodite." Similar views have long been held by some
authors, though until recently without a firm basis.
*(2) The male Thylacinus offers the best instance. Owen, Anatomy
of Vertebrates, vol. iii., p. 771.
*(3) Hermaphroditism has been observed in several species of
Serranus, as well as in some other fishes, where it is either normal
and symmetrical, or abnormal and unilateral. Dr. Zouteveen has given
me references on this subject, more especially to a paper by Prof.
Halbertsma, in the Transact. of the Dutch Acad. of Sciences, vol. xvi.
Dr. Gunther doubts the fact, but it has now been recorded by too
many good observers to be any longer disputed. Dr. M. Lessona writes
to me, that he has verified the observations made by Cavolini on
Serranus. Prof. Ercolani has recently shewn (Acad. delle Scienze,
Bologna, Dec. 28, 1871) that eels are androgynous.

The possession by male mammals of functionally imperfect mammary
organs is, in some respects, especially curious. The Monotremata
have the proper milk-secreting glands with orifices, but no nipples;
and as these animals stand at the very base of the mammalian series,
it is probable that the progenitors of the class also had
milk-secreting glands, but no nipples. This conclusion is supported by
what is known of their manner of development; for Professor Turner
informs me, on the authority of Kolliker and Langer, that in the
embryo the mammary glands can be distinctly traced before the
nipples are in the least visible; and the development of successive
parts in the individual generally represents and accords with the
development of successive beings in the same line of descent. The
marsupials differ from the Monotremata by possessing nipples; so
that probably these organs were first acquired by the marsupials,
after they had diverged from, and risen above, the Monotremata, and
were then transmitted to the placental mammals.* No one will suppose
that the marsupials still remained androgynous, after they had
approximately acquired their present structure. How then are we to
account for male mammals possessing mammae? It is possible that they
were first developed in the females and then transferred to the males,
but from what follows this is hardly probable.

* Prof. Gegenbaur has shewn (Jenaische Zeitschrift, Bd. vii., p.
212) that two distinct types of nipples prevail throughout the several
mammalian orders, but that it is quite intelligible how both could
have been derived from the nipples of the marsupials, and the latter
from those of the Monotremata. See, also, a memoir by Dr. Max Huss, on
the mammary glands, ibid., B. viii., p. 176.

It may be suggested, as another view, that long after the
progenitors of the whole mammalian class had ceased to be androgynous,
both sexes yielded milk, and thus nourished their young; and in the
case of the marsupials, that both sexes carried their young in
marsupial sacks. This will not appear altogether improbable, if we
reflect that the males of existing syngnathous fishes receive the eggs
of the females in their abdominal pouches, hatch them, and afterwards,
as some believe, nourish the young;* - that certain other male
fishes hatch the eggs within their mouths or branchial cavities;- that
certain male toads take the chaplets of eggs from the females, and
wind them round their own thighs, keeping them there until the
tadpoles are born;- that certain male birds undertake the whole duty
of incubation, and that male pigeons, as well as the females, feed
their nestlings with a secretion from their crops. But the above
suggestion first occurred to me from mammary glands of male mammals
being so much more perfectly developed than the rudiments of the other
accessory reproductive parts, which are found in the one sex though
proper to the other. The mammary glands and nipples, as they exist
in male mammals, can indeed hardly be called rudimentary; they are
merely not fully developed, and not functionally active. They are
sympathetically affected under the influence of certain diseases, like
the same organs in the female. They often secrete a few drops of
milk at birth and at puberty: this latter fact occurred in the curious
case before referred to, where a young man possessed two pairs of
mammee. In man and some other male mammals these organs have been
known occasionally to become so well developed during maturity as to
yield a fair supply of milk. Now if we suppose that during a former
prolonged period male mammals aided the females in nursing their
offspring,*(2) and that afterwards from some cause (as from the
production of a smaller number of young) the males ceased to give this
aid, disuse of the organs during maturity would lead to their becoming
inactive; and from two well-known principles of inheritance, this
state of inactivity would probably be transmitted to the males at
the corresponding age of maturity. But at an earlier age these
organs would be left unaffected, so that they would be almost
equally well developed in the young of both sexes.

* Mr. Lockwood believes (as quoted in Quart. Journal of Science,
April, 1868, p. 269), from what he has observed of the development
of Hippocampus, that the walls of the abdominal pouch of the male in
some way afford nourishment. On male fishes hatching the ova in
their mouths, see a very interesting paper by Prof. Wyman, in Proc.
Boston Soc. of Nat. Hist., Sept. 15, 1857; also Prof. Turner, in
Journal of Anatomy and Physiology, Nov. 1, 1866, p. 78. Dr. Gunther
has likewise described similar cases.
*(2) Mlle. C. Royer has suggested a similar view in her Origine de
l'homme, &c., 1870.

Conclusion.- Von Baer has defined advancement or progress in the
organic scale better than any one else, as resting on the amount of
differentiation and specialisation of the several parts of a being,-
when arrived at maturity, as I should be inclined to add. Now as
organisms have become slowly adapted to diversified lines of life by
means of natural selection, their parts will have become more and more
differentiated and specialised for various functions from the
advantage gained by the division of physiological labour. The same
part appears often to have been modified first for one purpose, and
then long afterwards for some other and quite distinct purpose; and
thus all the parts are rendered more and more complex. But each
organism still retains the general type of structure of the progenitor
from which it was aboriginally derived. In accordance with this view
it seems, if we turn to geological evidence, that organisation on
the whole has advanced throughout the world by slow and interrupted
steps. In the great kingdom of the Vertebrata it has culminated in
man. It must not, however, be supposed that groups of organic beings
are always supplanted, and disappear as soon as they have given
birth to other and more perfect groups. The latter, though
victorious over their predecessors, may not have become better adapted
for all places in the economy of nature. Some old forms appear to have
survived from inhabiting protected sites, where they have not been
exposed to very severe competition; and these often aid us in
constructing our genealogies, by giving us a fair idea of former and
lost populations. But we must not fall into the error of looking at
the existing members of any lowly-organised group as perfect
representatives of their ancient predecessors.
The most ancient progenitors in the kingdom of the Vertebrata, at
which we are able to obtain an obscure glance, apparently consisted of
a group of marine animals,* resembling the larvae of existing
ascidians. These animals probably gave rise to a group of fishes, as
lowly organised as the lancelet; and from these the ganoids, and other
fishes like the Lepidosiren, must have been developed. From such
fish a very small advance would carry us on to the amphibians. We have
seen that birds and reptiles were once intimately connected
together; and the Monotremata now connect mammals with reptiles in a
slight degree. But no one can at present say by what line of descent
the three higher and related classes, namely, mammals, birds, and
reptiles, were derived from the two lower vertebrate classes,
namely, amphibians and fishes. In the class of mammals the steps are
not difficult to conceive which led from the ancient Monotremata to
the ancient marsupials; and from these to the early progenitors of the
placental mammals. We may thus ascend to the Lemuridae; and the
interval is not very wide from these to the Simiadae. The Simiadae
then branched off into two great stems, the New World and Old World
monkeys; and from the latter, at a remote period, Man, the wonder
and glory of the Universe, proceeded.

* The inhabitants of the seashore must be greatly affected by the
tides; animals living either about the mean high-water mark, or
about the mean low-water mark, pass through a complete cycle of
tidal changes in a fortnight. Consequently, their food supply will
undergo marked changes week by week. The vital functions of such
animals, living under these conditions for many generations, can
hardly fail to run their course in regular weekly periods. Now it is a
mysterious fact that in the higher and now terrestrial Vertebrata,
as well as in other classes, many normal and abnormal processes one or
more whole weeks as their periods; this would be rendered intelligible
if the Vertebrata are descended from an animal allied to the
existing tidal ascidians. Many instances of such periodic processes
might be given, as the gestation of mammals, the duration of fevers,
&c. The hatching of eggs affords also a good example, for, according
to Mr. Bartlett (Land and Water, Jan. 7, 1871), the eggs of the pigeon
are hatched in two weeks; those of the fowl in three; those of the
duck in four; those of the goose in five; and those of the ostrich
in seven weeks. As far as we can judge, a recurrent period, if
approximately of the right duration for any process or function, would
not, when once gained, be liable to change; consequently it might be
thus transmitted through almost any number of generations. But if
the function changed, the period would have to change, and would be
apt to change almost abruptly by a whole week. This conclusion, if
sound, is highly remarkable; for the period of gestation in each
mammal, and the hatching of each bird's eggs, and many other vital
processes, thus betray to us the primordial birthplace of these
animals.

Thus we have given to man a pedigree of prodigious length, but
not, it may be said, of noble quality. The world, it has often been
remarked, appears as if it had long been preparing for the advent of
man: and this, in one sense is strictly true, for he owes his birth to
a long line of progenitors. If any single link in this chain had never
existed, man would not have been exactly what he now is. Unless we
wilfully close our eyes, we may, with our present knowledge,
approximately recognise our parentage; nor need we feel ashamed of it.
The most humble organism is something much higher than the inorganic
dust under our feet; and no one with an unbiased mind can study any
living creature, however humble, without being struck with
enthusiasm at its marvellous structure and properties.

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