Chapter I: Physical Evolution

It is well known that a species is usually represented by a great
number of individuals, distinguished from all other similar
associations by more or less numerous points of structure, color,
size, etc., and by habits and instincts also, to a certain extent;
that the individuals of such associations reproduce their like, and
cannot be produced by individuals of associations or species which
present differences of structure, color, etc., as defined by
naturalists; that the individuals of any such series or species are
incapable of reproducing with those of any other species, with some
exceptions; and that in the latter cases the offspring are usually
entirely infertile.

The hypothesis of Cuvier assumes that each species was created by
Divine power as we now find it at some definite point of geologic
time. The paleontologist holding this view sees, in accordance
therewith, a succession of creations and destructions marking the
history of life on our planet from its commencement.

The development hypothesis states that all existing species have
been derived from species of preëxistent geological periods, as
offspring or by direct descent; that there have been no total
destructions of life in past time, but only a transfer of it from
place to place, owing to changes of circumstance; that the types of
structure become simpler and more similar to each other as we trace
them from later to earlier periods; and that finally we reach the
simplest forms consistent with one or several original parent types
of the great divisions into which living beings naturally fall.

It is evident, therefore, that the hypothesis does not include
change of species by hybridization, nor allow the descent of living
species from any other _living_ species: both these propositions are
errors of misapprehension or misrepresentation.

In order to understand the history of creation of a complex being,
it is necessary to analyze it and ascertain of what it consists. In
analyzing the construction of an animal or plant we readily arrange
its characters into those which it possesses in common with other
animals or plants, and those in which it resembles none other: the
latter are its _individual_ characters, constituting its
individuality. Next we find a large body of characters, generally of
a very obvious kind, which it possesses in common with a generally
large number of individuals, which, taken collectively, all men are
accustomed to call a species; these characters we consequently name
_specific_. Thirdly, we find characters, generally in parts of the
body which are of importance in the activities of the animal, or
which lie in near relation to its mechanical construction in
details, which are shared by a still larger number of individuals
than those which were similar in specific characters. In other
words, it is common to a large number of species. This kind of
character we call _generic_, and the grouping it indicates is a
genus.

Farther analysis brings to light characters of organism which are
common to a still greater number of individuals; this we call a
_family_ character. Those which are common to still more numerous
individuals are the _ordinal_: they are usually found in parts of
the structure which have the closest connection with the whole
life-history of the being. Finally, the individuals composing many
orders will be found identical in some important character of the
systems by which ordinary life is maintained, as in the nervous and
circulatory: the divisions thus outlined are called _classes_.

By this process of analysis we reach in our animal or plant those
peculiarities which are common to the whole animal or vegetable
kingdom, and then we have exhausted the structure so completely that
we have nothing remaining to take into account beyond the
cell-structure or homogeneous protoplasm by which we know that it is
organic, and not a mineral.

The history of the origin of a type, as species, genus, order, etc.,
is simply the history of the origin of the structure or structures
which define those groups respectively. It is nothing more nor less
than this, whether a man or an insect be the object of
investigation.

EVIDENCES OF DERIVATION.

α. Of Specific Characters.

The evidences of derivation of species from species, within the
limits of the genus, are abundant and conclusive. In the first
place, the rule which naturalists observe in defining species is a
clear consequence of such a state of things. It is not amount and
degree of difference that determine the definition of species from
species, but it is the _permanency_ of the characters in all cases
and under all circumstances. Many species of the systems include
varieties and extremes of form, etc., which, were they at all times
distinct, and not connected by intermediate forms, would be
estimated as species by the same and other writers, as can be easily
seen by reference to their works.

Thus, species are either “restricted” or “protean,” the latter
embracing many, the former few variations; and the varieties
included by the protean species are often as different from each
other in their typical forms as are the “restricted” species. As an
example, the species _Homo sapiens_ (man) will suffice. His primary
varieties are as distinct as the species of many well-known genera,
but cannot be defined, owing to the existence of innumerable
intermediate forms between them.

As to the common origin of such “varieties” of the protean species,
naturalists never had any doubt, yet when it comes to the restricted
“species,” the anti-developmentalist denies it _in toto_. Thus the
varieties of most of the domesticated animals are some of them
known—others held with great probability to have had a common
origin. Varieties of plumage in fowls and canaries are of every-day
occurrence, and are produced under our eyes. The cart-horse and
racer, the Shetland pony and the Norman, are without doubt derived
from the same parentage. The varieties of pigeons and ducks are of
the same kind, but not every one is aware of the extent and amount
of such variations. The varieties in many characters seen in hogs
and cattle, especially when examples from distant countries are
compared, are very striking, and are confessedly equal in degree to
those found to _define_ species in a state of nature: here, however,
they are not _definitive_.

It is easy to see that all that is necessary to produce in the mind
of the anti-developmentalist the illusion of distinct origin by
creation of many of these forms, would be to destroy a number of the
intermediate conditions of specific form and structure, and thus to
leave remaining definable groups of individuals, and therefore
“species.”

That such destructions and extinctions have been going on ever since
the existence of life on the globe is well known. That it should
affect intermediate forms, such as bind together the types of a
protean species as well as restricted species, is equally certain.
That its result has been to produce _definable_ species cannot be
denied, especially in consideration of the following facts: Protean
species nearly always have a wide geographical distribution. They
exist under more varied circumstances than do individuals of a more
restricted species. The subordinate variations of the protean
species are generally, like the restricted species, confined to
distinct subdivisions of the geographical area which the whole
occupies. As in geological time changes of level have separated
areas once continuous by bodies of water or high mountain ranges, so
have vast numbers of individuals occupying such areas been
destroyed. Important alterations of temperature, or great changes in
abundance or character of vegetable life over given areas, would
produce the same result.

This part of the subject might be prolonged, were it necessary, but
it has been ably discussed by Darwin. The _rationale_ of the “origin
of species” as stated by him may be examined a few pages farther on.

β. Of the Characters of Higher Groups.

_a. Relations of Structures._ The evidences of derivative origin of
the structures defining the groups called genera, and all those of
higher grade, are of a very different character from those discussed
in relation to specific characters; they are more difficult of
observation and explanation.

Firstly: It would appear to be supposed by many that the creation of
organic types was an irregular and capricious process, variously
pursued by its Author as regards time and place, and without
definite final aim; and this notwithstanding the wonderful evidences
we possess, in the facts of astronomy, chemistry, sound, etc., of
His adhesion to harmonious and symmetrical sequences in His modes
and plans.

Such regularity of plan is found to exist in the relations of the
great divisions of the animal and vegetable kingdoms as at present
existing on the earth. Thus, with animals we have a great class of
species which consists of nothing more than masses or cells of
protoplasmic matter, without distinct organs; or the Protozoa. We
have then the Cœlenterata (example, corals,) where the organism is
composed of many cells arranged in distinct parts, but where a
single very simple system of organs, forming the only internal
cavity of the body, does the work of the many systems of the more
complex animals. Next, the Echinodermata (such as star-fish) present
us with a body containing distinct systems of organs enclosed in a
visceral cavity, including a rudimental nervous system in the form
of a ring. In the Molluscs to this condition is added additional
complication, including extensions of the nervous system from the
ring as a starting-point, and a special organ for a heart. In the
Articulates (crabs, insects,) we have like complications, and a long
distinct nervous axis on the lower surface of the body. The last
branch or division of animals is considered to be higher, because
all the systems of life organs are most complex or specialized. The
nervous ring is almost obliterated by a great enlargement of its
usual ganglia, thus become a brain, which is succeeded by a long
axis on the upper side of the body. This and other points define the
Vertebrata.

Plans of structure, independent of the simplicity or perfection of
the special arrangement or structure of organs, also define these
great groups. Thus the Protozoa present a spiral, the Cœlenterata a
radiate, the Echinodermata a bilateral radiate plan. The Articulates
are a series of external rings, each in one or more respects
repeating the others. The Molluscs are a sac, while a ring above a
ring, joined together by a solid center-piece, represents the plan
of each of the many segments of the Vertebrates which give the
members of that branch their form.

These bulwarks of distinction of animal types are entered into here
simply because they are the most inviolable and radical of those
with which we have to deal, and to give the anti-developmentalist
the best foothold for his position. I will only allude to the
relations of their points of approach, as these are affected by
considerations afterward introduced.

The Vertebrates approach the Molluscs at the lowest extreme of the
former and higher of the latter. The lamprey eels of the one possess
several characters in common with the cuttle-fish or squids of the
latter. The amphioxus is called the lowest Vertebrate, and though it
is nothing else, the definition of the division must be altered to
receive it; it has no brain!

The lowest forms of the Molluscs and Articulates are scarcely
distinguishable from each other, so far as adhesion to the “plan” is
concerned, and some of the latter division are very near certain
Echinodermata. As we approach the boundary-lines of the two lowest
divisions, the approaches become equally close, and the boundaries
very obscure.

More instructive is the evidence of the relation of the subordinate
classes of any one of these divisions. The conditions of those
organs or parts which define classes exhibit a regular relation,
commencing with simplicity and ending with complication; first
associated with weak exhibitions of the highest functions of the
nervous system—at the last displaying the most exalted traits found
in the series.

For example: In the classes of Vertebrates we find the lowest
nervous system presents great simplicity—the brain cannot be
recognized; next (in lampreys), the end of the nervous axis is
subdivided, but scarcely according to the complex type that follows.
In fishes the cerebellum and cerebral hemispheres are minute, and
the intermediate or optic lobes very large: in the reptiles the
cerebral hemispheres exceed the optic lobes, while the cerebellum is
smaller. In birds the cerebellum becomes complex and the cerebrum
greatly increases. In mammals the cerebellum increases in complexity
or number of parts, the optic lobes diminish, while the cerebral
hemispheres become wonderfully complex and enlarged, bringing us to
the highest development, in man.

The history of the circulatory system in the Vertebrates is the
same.[45] First, a heart with one chamber, then one with two
divisions: three divisions belong to a large series, and the highest
possess four. The origins of the great artery of the body, the
aorta, are first five on each side: they lose one in the succeeding
class in the ascending scale, and one in each succeeding class or
order, till the Mammalia, including man, present us with but one on
one side.

Footnote 45:

See a homological system of the circulatory system in the author’s
Origin of Genera, p. 22.

From an infinitude of such considerations as the above, we derive
the certainty that the general arrangement of the various groups of
the organic world is in scales, the subordinate within the more
comprehensive divisions. The identification of all the parts in such
a complexity of organism as the highest animals present, is a matter
requiring much care and attention, and constitutes the study of
homologies. Its pursuit has resulted in the demonstration that every
individual of every species of a given branch of the animal kingdom
is composed of elements common to all, and that the differences
which are so radical in the higher groups are but the modifications
of the same elemental parts, representing completeness or
incompleteness, obliteration or subdivision. Of the former character
are rudimental organs, of which almost every species possesses an
example in some part of its structure.

But we have other and still more satisfactory evidence of the
meaning of these relations. By the study of embryology we can prove
most indubitably that the simple and less complex are inferior to
the more complex. Selecting the Vertebrates again as an example, the
highest form of mammal—_e.g._, man—presents in his earliest stages
of embryonic growth a skeleton of cartilage, like that of the
lamprey: he also possesses five origins of the aorta and five slits
on the neck, both which characters belong to the lamprey and the
shark. If the whole number of these parts does not coexist in the
embryonic man, we find in embryos of lower forms more nearly related
to the lamprey that they do. Later in the life of the mammal but
four aortic origins are found, which arrangement, with the heart now
divided into two chambers, from a beginning as a simple tube, is
characteristic of the class of Vertebrates next in order—the bony
fishes. The optic lobes of the human brain have also at this time a
great predominance in size—a character above stated to be that of
the same class. With advancing development the infant mammal follows
the scale already pointed out. Three chambers of the heart and three
aortic origins follow, presenting the condition permanent in the
batrachia; and two origins, with enlarged cerebral hemispheres of
the brain, resemble the reptilian condition. Four heart-chambers,
and one aortic root on each side, with slight development of the
cerebellum, follow all characters defining the crocodiles, and
immediately precede the special conditions defining the mammals.
These are, the single aorta root from one side, and the full
development of the cerebellum: later comes that of the cerebrum also
in its higher mammalian and human traits.

Thus we see the order already pointed out to be true, and to be an
ascending one. This is the more evident as each type or class passes
through the conditions of those below it, as did the mammal; each
scale being shorter as its highest terminus is lower. Thus the
crocodile passes through the stage of the lamprey, the fish, the
batrachian and the reptile proper.

_b. In Time._ We have thus a scale of relations of existing forms of
animals and plants of a remarkable kind, and such as to stimulate
greatly our inquiries as to its significance. When we turn to the
remains of the past creation preserved to us in the deposits
continued throughout geologic time, we are not disappointed, for
great light is at once thrown upon the subject.

We find, in brief, that the lowest division of the animal kingdom
appeared first, and long before any type of a higher character was
created. The Protozoön, Eozoön, is the earliest of animals in
geologic time, and represents the lowest type of animal life now
existing. We learn also that the highest branch appeared last. No
remains of Vertebrates have been found below the lower Devonian
period, or not until the Echinoderms and Molluscs had reached a
great preëminence. It is difficult to be sure whether the Protozoa
had a greater numerical extent in the earliest periods than now, but
there can be no doubt that the Cœlenterata (corals) and Echinoderms
(crinoids) greatly exceeded their present bounds, in Paleozoic time,
so that those at present existing are but a feeble remnant. If we
examine the subdivisions known as classes, evidence of the nature of
the succession of creation is still more conclusive. The most
polyp-like of the Molluscs (brachiopoda) constituted the great mass
of its representatives during Paleozoic time. Among Vertebrates the
fishes appear first, and had their greatest development in size and
numbers during the earliest periods of the existence of the
division. Batrachia were much the largest and most important of land
animals during the Carboniferous period, while the higher
Vertebrates were unknown. The later Mesozoic periods saw the reign
of reptiles, whose position in structural development has been
already stated. Finally, the most perfect, the mammal, came upon the
scene, and in his humblest representatives. In Tertiary times
mammalia supplanted the reptiles entirely, and the unspiritual
mammals now yield to man, the only one of his class in whom the
Divine image appears.

Thus the structural relations, the embryonic characters, and the
successive appearance in time of animals coincide. The same is very
probably true of plants.

That the existing state of the geological record of organic types
should be regarded as anything but a fragment is, from our
stand-point, quite preposterous. And more, it may be assumed with
safety that when completed it will furnish us with a series of
regular successions, with but slight and regular interruptions, if
any, from the species which represented the simplest beginnings of
life at the dawn of creation, to those which have displayed
complication and power in later or in the present period.

For the labors of the paleontologist are daily bringing to light
structures intermediate between those never before so connected, and
thus creating lines of succession where before were only
interruptions. Many such instances might be adduced: two may be
selected as examples from American paleontology;[46] _i.e._, the
near approach to birds made by the reptiles Lælaps and Megadactylus;
and the combination of characters of the sub-orders of Cryptodire
and Pleurodire Tortoises in the Adocus of New Jersey.

Footnote 46:

Professor Huxley, in the last anniversary lecture before the
Geological Society of London, recalls his opinion, enunciated in
1862, that “the positively-ascertained truths of Paleontology”
negative “the doctrines of progressive modification, which suppose
that modification to have taken place by a necessary progress from
more to less embryonic forms, from more to less generalized types,
within the limits of the period represented by the fossiliferous
rocks; that it shows no evidence of such modification; and as to
the nature of that modification, it yields no evidence whatsoever
that the earlier members of any long-continued group were more
generalized in structure than the later ones.”

Respecting this position, he says: “Thus far I have endeavored to
expand and enforce by fresh arguments, but not to modify in any
important respect, the ideas submitted to you on a former
occasion. But when I come to the propositions respecting
progressive modification, it appears to me, with the help of the
new light which has broken from various quarters, that there is
much ground for softening the somewhat Brutus-like severity with
which I have dealt with a doctrine for the truth of which I should
have been glad enough to be able to find a good foundation in
1862. So far indeed as the Invertebrata and the lower Vertebrata
are concerned, the facts, and the conclusions which are to be
drawn from them, appear to me to remain what they were. For
anything that as yet appears to the contrary, the earliest known
marsupials may have been as highly organized as their living
congeners; the Permian lizards show no signs of inferiority to
those of the present day; the labyrinthodonts cannot be placed
below the living salamander and triton; the Devonian ganoids are
closely related to polypterus and lepidosiren.”

To this it may be replied: 1. The scale of progression of the
Vertebrata is measured by the conditions of the circulatory
system, and in some measure by the nervous, and not by the
osseous: tested by this scale, there has been successional
complication of structure among Vertebrata in time. 2. The
question with the evolutionist is, not what types have persisted
to the present day, but the order in which types appeared in time.
3. The Marsupials, Permian saurians, labyrinthodonts and Devonian
ganoids are remarkably generalized groups, and predecessors of
types widely separated in the present period. 4. Professor Huxley
adduces many such examples among the mammalian subdivisions in the
remaining portion of his lecture. 5. Two alternatives are yet open
in the explanation of the process of evolution: since generalized
types, which combine the characters of higher and lower groups of
later periods, must thus be superior to the lower, the lower must
(first) be descended from such a generalized form by degradation;
or (second) not descended from it at all, but from some lower
contemporaneous type by advance; the higher only of the two being
derived from the first-mentioned. The last I suspect to be a true
explanation, as it is in accordance with the homologous groups.
This law will shorten the demands of paleontologists for time,
since, instead of deriving all reptilia, batrachia, etc., from
common origins, it points to the derivation of higher reptilia of
a higher order from higher reptilia of a lower order, lower
reptilia of the first from lower reptilia of the second; finally,
the several groups of the lowest or most generalized order of
reptilia from a parallel series of the class below, or batrachia.

We had no more reason to look for intermediate or connecting forms
between such types as these, than between any others of similar
degree of remove from each other with which we are acquainted. And
inasmuch as almost all groups, as genera, orders, etc., which are
held to be distinct, but adjacent, present certain points of
approximation to each other, the almost daily discovery of
intermediate forms gives us confidence to believe that the pointings
in other cases will also be realized.

γ. Of Transitions.

The preceding statements were necessary to the comprehension of the
supposed mode of metamorphosis or development of the various types
of living beings, or, in other words, of the single structural
features which define them.... As it is evident that the more
comprehensive groups, or those of highest rank, have had their
origin in remote ages, cases of transition from one to the other by
change of character cannot be witnessed at the present day. We
therefore look to the most nearly related divisions, or those of the
lowest rank, for evidence of such change.

It is necessary to premise that embryology teaches that all the
species of a given branch of the animal kingdom (_e.g._, Vertebrate,
Mollusc, etc.) are quite identical in structural character at their
first appearance on the germinal layer of the yolk of the parent
egg. It shows that the character of the respective groups of high
rank appear first, then those of less grade, and last of all those
structures which distinguish them as genera. But among the earliest
characters which appear are those of the species, and some of those
of the individual.

We find the characters of different _genera_ to bear the same
relation to each other that we have already seen in the case of
those definitive of orders, etc. In a natural assemblage of related
genera we discover that some are defined by characters found only in
the embryonic stages of others; while a second will present a
permanent condition of its definitive part, which marks a more
advanced stage of that highest. In this manner many stages of the
highest genus appear to be represented by permanent genera in all
natural groups. Generally, however, this resemblance does not
involve, an entire identity, there being some other immaturities
found in the highest genus at the time it presents the character
preserved in permanency by the lower, which the lower loses. Thus
(to use a very coarse example) a frog at one stage of growth has
four legs and a tail: the salamander always preserves four legs and
a tail, thus resembling the young frog. The latter is, however, not
a salamander at that time, because, among other things, the skeleton
is represented by cartilage only, and the salamander’s is ossified.
This relation is therefore an imitation only, and is called _inexact
parallelism_.

As we compare nearer and nearer relations—_i.e._, the genera which
present fewest points of difference—we find the differences between
undeveloped stages of the higher and permanent conditions of the
lower to grow fewer and fewer, until we find numerous instances
where the lower genus is exactly the same as the undeveloped stage
of the higher. This relation is called that of _exact parallelism_.

It must now be remembered that the permanence of a character is what
gives it its value in defining genus, order, etc., in the eyes of
the systematist. So long as the condition is permanent no transition
can be seen: there is therefore no development. If the condition is
transitional, it defines nothing, and nothing is developed; at
least, so says the anti-developmentalist. It is the old story of the
settler and the Indian: “Will you take owl and I take turkey, or I
take turkey and you owl?”

If we find a relation of _exact parallelism_ to exist between two
sets of species in the condition of a certain organ, and the
difference so expressed the only one which distinguishes them as
sets from each other—if that condition is always the same in each
set—we call them two genera: if in any species the condition is
variable at maturity, or sometimes the undeveloped condition of the
part is persistent and sometimes transitory, the sets characterized
by this difference must be united by the systematist, and the whole
is called a single genus.

We know numerous cases where different individuals of the same
species present this relation of _exact parallelism_ to each other;
and as we ascribe common origin to the individuals of a species, we
are assured that the condition of the inferior individual is, in
this case, simply one of repressed growth, or a failure to fulfill
the course accomplished by the highest. Thus, certain species of the
salamandrine genus amblystoma undergo a metamorphosis involving
several parts of the osseous and circulatory systems, etc., while
half grown; others delay it till fully grown; one or two species
remain indifferently unchanged or changed, and breed in either
condition, while another species breeds unchanged, and has never
been known to complete a metamorphosis.

The nature of the relation of _exact parallelism_ is thus explained
to be that of checked or advanced growth of individuals having a
common origin. The relation of _inexact parallelism_ is readily
explained as follows: With a case of _exact parallelism_ in the
mind, let the repression producing the character of the lower,
parallelize the latter with a stage of the former in which a second
part is not quite mature: we will have a slight want of
correspondence between the two. The lower will be immature in but
one point, the incompleteness of the higher being seen in two
points. If we suppose the immaturity to consist in a repression at a
still earlier point in the history of the higher, the latter will be
undeveloped in other points also: thus, the spike-horned deer of
South America have the horn of the second year of the North American
genus. They would be generically identical with that stage of the
latter, were it not that these still possess their milk dentition at
two years of age. In the same way the nature of the parallelisms
seen in higher groups, as orders, etc., may be accounted for.

The theory of homologous groups furnishes important evidence in
favor of derivation. Many orders of animals (probably all, when we
come to know them) are divisible into two or more sections, which I
have called _homologous_. These are series of genera or families,
which differ from each other by some marked character, but whose
contained genera or families differ from each other in the same
points of detail, and in fact correspond exactly. So striking is
this correspondence that were it not for the general and common
character separating the homologous series, they would be regarded
as the same, each to each. Now it is remarkable that where studied
the difference common to all the terms of two homologous groups is
found to be one of _inexact parallelism_, which has been shown above
to be evidence of descent. Homologous groups always occupy different
geographical areas on the earth’s surface, and their relation is
precisely that which holds between successive groups of life in the
periods of geologic time.

In a word, we learn from this source that distinct geologic epochs
coexist at the same time on the earth. I have been forced to this
conclusion[47] by a study of the structure of terrestrial life, and
it has been remarkably confirmed by the results of recent deep-sea
dredgings made by the United States Coast Survey in the Gulf Stream,
and by the British naturalists in the North Atlantic. These have
brought to light types of Tertiary life, and of even the still more
ancient Cretaceous periods, living at the present day. That this
discovery invalidates in any wise the conclusions of geology
respecting lapse of time is an unwarranted assumption that some are
forward to make. If it changes the views of some respecting the
parallelism or coëxistence of faunæ in different regions of the
earth, it is only the anti-developmentalists whose position must be
changed.

Footnote 47:

_Origin of Genera_, pages 70, 77, 79.

For, if we find distinct geologic faunæ, or epochs defined by faunæ,
coëxisting during the present period, and fading or emerging into
one another as they do at their geographical boundaries, it is proof
positive that the geologic epochs and periods of past ages had in
like manner no trenchant boundaries, but also passed the one into
the other. The assumption that the apparent interruptions are the
result of transfer of life rather than destruction, or of want of
opportunities of preservation, is no doubt the true one.

δ. Rationale of Development.

_a. In Characters of Higher Groups._ It is evident in the case of
the species in which there is an irregularity in the time of
completion of metamorphosis that some individuals traverse a longer
developmental line than those who remain more or less incomplete. As
both accomplish growth in the same length of time, it is obvious
that it proceeds with greater rapidity in one sense in that which
accomplishes most: its growth is said to be accelerated. This
phenomenon is especially common among insects, where the females of
perfect males are sometimes larvæ or nearly so, or pupæ, or lack
wings or some character of final development. Quite as frequently,
some males assume characters in advance of others, sometimes in
connection with a peculiar geographical range.

In cases of _exact parallelism_ we reasonably suppose the cause to
be the same, since the conditions are identical, as has been shown;
that is, the higher conditions have been produced by a crowding back
of the earlier characters and an acceleration of growth, so that a
given succession in order of advance has extended over a longer
range of growth than its predecessor in the same allotted time. That
allotted time is the period before maturity and reproduction, and it
is evident that as fast as modifications or characters should be
assumed sufficiently in advance of that period, so certainly would
they be conferred upon the offspring by reproduction. The
_acceleration_ in the assumption of a character, progressing more
rapidly than the same in another character, must soon produce, in a
type whose stages were once the exact parallel of a permanent lower
form, the condition of _inexact parallelism_. As all the more
comprehensive groups present this relation to each other, we are
compelled to believe that _acceleration_ has been the principle of
their successive evolution during the long ages of geologic time.

Each type has, however, its day of supremacy and perfection of
organism, and a retrogression in these respects has succeeded. This
has no doubt followed a law the reverse of acceleration, which has
been called _retardation_. By the increasing slowness of the growth
of the individuals of a genus, and later and later assumption of the
characters of the latter, they would be successively lost.

To what power shall we ascribe this acceleration, by which the first
beginnings of structure have accumulated to themselves through the
long geologic ages complication and power, till from the germ that
was scarcely born into a sand-lance, a human being climbed the
complete scale, and stood easily the chief of the whole?

In the cases of species, where some individuals develop farther than
others, we say the former possess more growth-force, or “vigor,”
than the latter. We may therefore say that higher types of structure
possess more “vigor” than the lower. This, however, we do not know
to be true, nor can we readily find means to demonstrate it.

The food which is taken by an adult animal is either assimilated, to
be consumed in immediate activity of some kind, or stored for future
use, and the excess is rejected from the body. We have no reason to
suppose that the same kind of material could be made to subserve the
production of life-force by any other means than that furnished by a
living animal organism. The material from which this organism is
constructed is derived first from the parent, and afterward from the
food, etc., assimilated by the individual itself so long as growth
continues. As it is the activity of assimilation directed to a
special end during this latter period which we suppose to be
increased in accelerated development, the acceleration is evidently
not brought about by increased facilities for obtaining the means of
life which the same individual possesses as an adult. That it is not
in consequence of such increased facilities possessed by its parents
over those of the type preceding it, seems equally improbable when
we consider that the characters in which the parent’s advance has
appeared are rarely of a nature to increase those facilities.

The nearest approach to an explanation that can be offered appears
to be somewhat in the following direction:

There is every reason to believe that the character of the
atmosphere has gradually changed during geologic time, and that
various constituents of the mixture have been successively removed
from it, and been stored in the solid material of the earth’s crust
in a state of combination. Geological chemistry has shown that the
cooling of the earth has been accompanied by the precipitation of
many substances only gaseous at high temperatures. Hydrochloric and
sulphuric acids have been transferred to mineral deposits or aqueous
solutions. The removal of carbonic acid gas and the vapor of water
has been a process of much slower progress, and after the expiration
of all the ages a proportion of both yet remains. Evidence of the
abundance of the former in the earliest periods is seen in the vast
deposits of limestone rock; later, in the prodigious quantities of
shells which have been elaborated from the same in solution. Proof
of its abundance in the atmosphere in later periods is seen in the
extensive deposits of coal of the Carboniferous, Triassic and
Jurassic periods. If the most luxuriant vegetation of the present
day takes but fifty tons of carbon from the atmosphere in a century,
per acre, thus producing a layer over that extent of less than a
third of an inch in thickness, what amount of carbon must be
abstracted in order to produce strata of thirty-five feet in depth?
No doubt it occupied a long period, but the atmosphere, thus
deprived of a large proportion of carbonic acid, would in subsequent
periods undoubtedly possess an improved capacity for the support of
animal life.

The successively higher degree of oxidization of the blood in the
organs designed for that function, whether performing it in water or
air, would certainly accelerate the performances of all the vital
functions, and among others that of growth. Thus it may be that
_acceleration_ can be accounted for, and the process of the
development of the orders and sundry lesser groups of the Vertebrate
kingdom indicated; for, as already pointed out, the definitions of
such are radically placed in the different structures of the organs
which aerate the blood and distribute it to its various
destinations.

But the great question, What determined the direction of this
acceleration? remains unanswered. One cannot understand why more
highly-oxidized blood should hasten the growth of partition of the
ventricle of the heart in the serpent, the more perfectly to
separate the aerated from the impure fluid; nor can we see why a
more perfectly-constructed circulatory system, sending purer blood
to the brain, should direct accelerated growth to the cerebellum or
cerebral hemispheres in the crocodile.

_b. In Characters of the Specific Kind._ Some of the characters
usually placed in the specific category have been shown to be the
same in kind as those of higher categories. The majority are,
however, of a different kind, and have been discussed several pages
back.

The cause of the origin of these characters is shrouded in as much
mystery as that of those which have occupied the pages immediately
preceding. As in that case, we have to assume, as Darwin has done, a
tendency in Nature to their production. This is what he terms “the
principle of variation.” Against an unlimited variation the great
law of heredity or atavism has ever been opposed, as a conservator
and multiplier of type. This principle is exemplified in the fact
that like produces like—that children are like their parents,
frequently even in minutiæ. It may be compared to habit in
metaphysical matters, or to that singular love of time or rhythm
seen in man and lower animals, in both of which the tendency is to
repeat in continual cycles a motion or state of the mind or sense.

Further, but a proportion of the lines of variation is supposed to
have been perpetuated, and the extinction of intermediate forms, as
already stated, has left isolated groups or species.

The effective cause of these extinctions is stated by Darwin to have
been a “natural selection”—a proposition which distinguishes his
theory from other development hypotheses, and which is stated in
brief by the expression, “the preservation of the fittest.” Its
meaning is this: that those characters appearing as results of this
spontaneous variation which are little adapted to the conflict for
subsistence, with the nature of the supply, or with rivals in its
pursuit, dwindle and are sooner or later extirpated; while those
which are adapted to their surroundings, and favored in the struggle
for means of life and increase, predominate, and ultimately become
the centers of new variation. “I am convinced,” says Darwin, “that
natural selection has been the main, but not exclusive, means of
modification.”

That it has been to a large extent the means of preservation of
those structures known as specific, must, I think, be admitted. They
are related to their peculiar surroundings very closely, and are
therefore more likely to exist under their influence. Thus, if a
given genus extends its range over a continent, it is usually found
to be represented by peculiar species—one in a maritime division,
another in the desert, others in the forest, in the swamp or the
elevated areas of the region. The wonderful interdependence shown by
Darwin to exist between insects and plants in the fertilization of
the latter, or between animals and their food-plants, would almost
induce one to believe that it were the true expression of the whole
law of development.

But the following are serious objections to its universal
application:

First: The characters of the higher groups, from genera up, are
rarely of a character to fit their possessors especially for
surrounding circumstances; that is, the differences which separate
genus from genus, order from order, etc., in the ascending scale of
each, do not seem to present a superior adaptation to surrounding
circumstances in the higher genus to that seen in the lower genus,
etc. Hence, superior adaptation could scarcely have caused their
selection above other forms not existing. Or, in other words, the
different structures which indicate successional relation, or which
measure the steps of progress, seem to be equally well fitted for
the same surroundings.

Second: The higher groups, as orders, classes, etc., have been in
each geologic period alike distributed over the whole earth, under
all the varied circumstances offered by climate and food. Their
characters do not seem to have been modified in reference to these.
Species, and often genera, are, on the other hand, eminently
restricted according to climate, and consequently vegetable and
animal food.

The law of development which we seek is indeed not that which
preserves the higher forms and rejects the lower after their
creation, but that which explains why higher forms were created at
all. Why in the results of a creation we see any relation of higher
and lower, and not rather a world of distinct types, each perfectly
adapted to its situation, but none properly higher than another in
an ascending scale, is the primary question. Given the principle of
advance, then natural selection has no doubt modified the details;
but in the successive advances we can scarcely believe such a
principle to be influential. _We look rather upon a progress as the
result of the expenditure of some force fore-arranged for that end._

It may become, then, a question whether in characters of high grade
the habit or use is not rather the result of the acquisition of the
structure than the structure the result of the encouragement offered
to its assumed beginnings by use, or by liberal nutrition derived
from the increasingly superior advantages it offers.

ε. The Physical Origin of Man.

If the hypothesis here maintained be true, man is the descendant of
some preëxistent generic type, the which, if it were now living, we
would probably call an ape.

Man and the chimpanzee were in Linnæus’ system only two species of
the same genus, but a truer anatomy places them in separate genera
and distinct families. There is no doubt, however, that Cuvier went
much too far when he proposed to consider Homo as the representative
of an order distinct from the quadrumana, under the name of bimana.
The structural differences will not bear any such interpretation,
and have not the same value as those distinguishing the orders of
mammalia; as, for instance, between carnivora and bats, or the
cloven-footed animals and the rodents, or rodents and edentates. The
differences between man and the chimpanzee are, as Huxley well puts
it, much less than those between the chimpanzee and lower
quadrumana, as lemurs, etc. In fact, man is the type of a family,
Hominidæ, of the order Quadrumana, as indicated by the characters of
the dentition, extremities, brain, etc. The reader who may have any
doubts on this score may read the dissections of Geoffroy St.
Hilaire, made in 1856, before the issue of Darwin’s _Origin of
Species_. He informs us that the brain of man is nearer in structure
to that of the orang than the orang’s is to that of the South
American howler, and that the orang and howler are more nearly
related in this regard than are the howler and the marmoset.

The modifications presented by man have, then, resulted from an
acceleration in development in some respects, and retardation
perhaps in others. But until the _combination_ now characteristic of
the genus Homo was attained the being could not properly be called
man.

And here it must be observed that as an organic type is
characterized by the coëxistence of a number of peculiarities which
have been developed independently of each other, its distinctive
features and striking functions are not exhibited until that
coëxistence is attained which is necessary for these ends.

Hence, the characters of the human genus were probably developed
successively; but few of the indications of human superiority
appeared until the combination was accomplished. Let the opposable
thumb be first perfected, but of what use would it be in human
affairs without a mind to direct? And of what use a mind without
speech to unlock it? And speech could not be possible though all the
muscles of the larynx but one were developed, or but a slight
abnormal convexity in one pair of cartilages remained.

It would be an objection of little weight could it be truly urged
that there have as yet no remains of apelike men been discovered,
for we have frequently been called upon in the course of
paleontological discovery to bridge greater gaps than this, and
greater remain, which we expect to fill. But we _have_ apelike
characters exhibited by more than one race of men yet existing.

But the remains of that being which is supposed to have been the
progenitor of man may have been discovered a short time since in the
cave of Naulette, Belgium, with the bones of the extinct rhinoceros
and elephant.

We all admit the existence of higher and lower races, the latter
being those which we now find to present greater or less
approximations to the apes. The peculiar structural characters that
belong to the negro in his most typical form are of that kind,
however great may be the distance of his remove therefrom. The
flattening of the nose and prolongation of the jaws constitute such
a resemblance; so are the deficiency of the calf of the leg, and the
obliquity of the pelvis, which approaches more the horizontal
position than it does in the Caucasian. The investigations made at
Washington during the war with reference to the physical
characteristics of the soldiers show that the arms of the negro are
from one to two inches longer than those of the whites: another
approximation to the ape. In fact, this race is a species of the
genus Homo, as distinct in character from the Caucasian as those we
are accustomed to recognize in other departments of the animal
kingdom; but he is not distinct by isolation, since intermediate
form’s between him and the other species can be abundantly found.

And here let it be particularly observed that two of the most
prominent characters of the negro are those of immature stages of
the Indo-European race in its characteristic types. The deficient
calf is the character of infants at a very early stage; but, what is
more important, the flattened bridge of the nose and shortened nasal
cartilages are universally immature conditions of the same parts in
the Indo-European. Any one may convince himself of that by examining
the physiognomies of infants. In some races—_e.g._, the Slavic—this
undeveloped character persists later than in some others. The Greek
nose, with its elevated bridge, coincides not only with æsthetic
beauty, but with developmental perfection.

This is, however, only “_inexact_ parallelism,” as the characters of
the hair, etc., cannot be explained on this principle _among
existing races_. The embryonic characters mentioned are probably a
remnant of those characteristic of the primordial race or species.

But the man of Naulette, if he be not a monstrosity, in a still more
distinct and apelike species. The chin, that marked character of
other species of men, is totally wanting, and the dentition is quite
approximate to the man-like apes, and different from that of modern
men. The form is very massive, as in apes. That he was not abnormal
is rendered probable by approximate characters seen in a jaw from
the cave of Puy-sur-Aube, and less marked in the lowest races of
Australia and New Caledonia.

As to the single or multiple origin of man, science as yet furnishes
no answer. It is very probable that, in many cases, the species of
one genus have descended from corresponding species of another by
change of generic characters only. It is a remarkable fact that the
orang possesses the peculiarly developed malar bones and the copper
color characteristic of the Mongolian inhabitants of the regions in
which this animal is found, while the gorilla exhibits the
prognathic jaws and black hue of the African races near whom he
dwells. This kind of geographical imitation is very common in the
animal kingdom.

ζ. The Mosaic Account.

As some persons imagine that this hypothesis conflicts with the
account of the creation of man given in Genesis, a comparison of
some of the points involved is made below.

First: In Genesis i. 26, 27, we read, “And God said, Let us make man
in our image, after our likeness,” etc. “So God created man in his
own image, in the image of God created he him; male and female
created he them.” Those who believe that this “image” is a physical,
material form, are not disposed to admit the entrance of anything
apelike into its constitution, for the ascription of any such
appearance to the Creator would be impious and revolting. But we are
told that “God is a Spirit,” and Christ said to his disciples after
his resurrection, “A spirit hath not flesh and bones, as ye see me
have.” Luke xxiv. 39. It will require little further argument to
show that a mental and spiritual image is what is meant, as it is
what truly exists. Man’s conscience, intelligence and creative
ingenuity show that he possesses an “image of God” within him, the
possession of which is really necessary to his limited comprehension
of God and of God’s ways to man.

Second: In Genesis ii. 7, the text reads, “And the Lord God formed
man of the dust of the ground, and breathed into his nostrils the
breath of life; and man became a living soul.” The fact that man is
the result of the modification of an apelike predecessor nowise
conflicts with the above statement as to the materials of which his
body is composed. Independently of origin, if the body of man be
composed of dust, so must that of the ape be, since the composition
of the two is identical. But the statement simply asserts that man
was created of the same materials which compose the earth: their
condition as “dust” depending merely on temperature and subdivision.
The declaration, “Dust thou art, and unto dust thou shalt return,”
must be taken in a similar sense, for we know that the decaying body
is resolved not only into its earthly constituents, but also into
carbonic acid gas and water.

When God breathed into man’s nostrils the breath of life, we are
informed that he became, not a living body, but “a living soul.” His
descent from a preëxistent being involved the possession of a living
body; but when the Creator breathed into him we may suppose for the
present that He infused into this body the immortal part, and at
that moment man became a conscientious and responsible being.