of the latter, it is hoped that they may be such as any logical mind
would deduce from the premises. That they will coincide with the
spirit of the most advanced Christianity, I have no doubt; and that
they will add an appeal through the reason to that direct influence
of the Divine Spirit which should control the motives of human
action, seems an unavoidable conclusion.
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.