David Hume - "An Enquiry Concerning the Principles of Morals"

C.F. McGlashan - "History of the Donner Party"

Richard Harding Davis - "Notes of a War Correspondent"

Sir Richard Francis Burton - "Personal Narrative of a Pilgrimage to Al Madinah and Meccah"

New Philadelphia Book Publisher Highlights Local Talent
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FlatSigned Press Alleges Don Imus Remarks Damage Legacy of President Gerald R. Ford
NEW YORK, N.Y. -- Nathan Yungerberg, an accomplished model scout and professional child photographer is launching a nation-wide casting call to find the cover model for his highly anticipated book release, 'The Model Child: A Parents Guide to the Child Modeling Industry' (ISBN: 978-0-9817018-0-6).

Books: On the Origin of Species

C >> Charles Darwin >> On the Origin of Species




Practically when naturalists are at work, they do not trouble
themselves about the physiological value of the characters which they
use in defining a group, or in allocating any particular species. If
they find a character nearly uniform, and common to a great number of
forms, and not common to others, they use it as one of high value; if
common to some lesser number, they use it as of subordinate value.
This principle has been broadly confessed by some naturalists to be
the true one; and by none more clearly than by that excellent
botanist, Aug. St. Hilaire. If certain characters are always found
correlated with others, though no apparent bond of connexion can be
discovered between them, especial value is set on them. As in most
groups of animals, important organs, such as those for propelling the
blood, or for aerating it, or those for propagating the race, are
found nearly uniform, they are considered as highly serviceable in
classification; but in some groups of animals all these, the most
important vital organs, are found to offer characters of quite
subordinate value.

We can see why characters derived from the embryo should be of equal
importance with those derived from the adult, for our classifications
of course include all ages of each species. But it is by no means
obvious, on the ordinary view, why the structure of the embryo should
be more important for this purpose than that of the adult, which alone
plays its full part in the economy of nature. Yet it has been strongly
urged by those great naturalists, Milne Edwards and Agassiz, that
embryonic characters are the most important of any in the
classification of animals; and this doctrine has very generally been
admitted as true. The same fact holds good with flowering plants, of
which the two main divisions have been founded on characters derived
from the embryo,--on the number and position of the embryonic leaves
or cotyledons, and on the mode of development of the plumule and
radicle. In our discussion on embryology, we shall see why such
characters are so valuable, on the view of classification tacitly
including the idea of descent.

Our classifications are often plainly influenced by chains of
affinities. Nothing can be easier than to define a number of
characters common to all birds; but in the case of crustaceans, such
definition has hitherto been found impossible. There are crustaceans
at the opposite ends of the series, which have hardly a character in
common; yet the species at both ends, from being plainly allied to
others, and these to others, and so onwards, can be recognised as
unequivocally belonging to this, and to no other class of the
Articulata.

Geographical distribution has often been used, though perhaps not
quite logically, in classification, more especially in very large
groups of closely allied forms. Temminck insists on the utility or
even necessity of this practice in certain groups of birds; and it has
been followed by several entomologists and botanists.

Finally, with respect to the comparative value of the various groups
of species, such as orders, sub-orders, families, sub-families, and
genera, they seem to be, at least at present, almost arbitrary.
Several of the best botanists, such as Mr. Bentham and others, have
strongly insisted on their arbitrary value. Instances could be given
amongst plants and insects, of a group of forms, first ranked by
practised naturalists as only a genus, and then raised to the rank of
a sub-family or family; and this has been done, not because further
research has detected important structural differences, at first
overlooked, but because numerous allied species, with slightly
different grades of difference, have been subsequently discovered.

All the foregoing rules and aids and difficulties in classification
are explained, if I do not greatly deceive myself, on the view that
the natural system is founded on descent with modification; that the
characters which naturalists consider as showing true affinity between
any two or more species, are those which have been inherited from a
common parent, and, in so far, all true classification is
genealogical; that community of descent is the hidden bond which
naturalists have been unconsciously seeking, and not some unknown plan
of creation, or the enunciation of general propositions, and the mere
putting together and separating objects more or less alike.

But I must explain my meaning more fully. I believe that the
ARRANGEMENT of the groups within each class, in due subordination and
relation to the other groups, must be strictly genealogical in order
to be natural; but that the AMOUNT of difference in the several
branches or groups, though allied in the same degree in blood to their
common progenitor, may differ greatly, being due to the different
degrees of modification which they have undergone; and this is
expressed by the forms being ranked under different genera, families,
sections, or orders. The reader will best understand what is meant, if
he will take the trouble of referring to the diagram in the fourth
chapter. We will suppose the letters A to L to represent allied
genera, which lived during the Silurian epoch, and these have
descended from a species which existed at an unknown anterior period.
Species of three of these genera (A, F, and I) have transmitted
modified descendants to the present day, represented by the fifteen
genera (a14 to z14) on the uppermost horizontal line. Now all these
modified descendants from a single species, are represented as related
in blood or descent to the same degree; they may metaphorically be
called cousins to the same millionth degree; yet they differ widely
and in different degrees from each other. The forms descended from A,
now broken up into two or three families, constitute a distinct order
from those descended from I, also broken up into two families. Nor can
the existing species, descended from A, be ranked in the same genus
with the parent A; or those from I, with the parent I. But the
existing genus F14 may be supposed to have been but slightly modified;
and it will then rank with the parent-genus F; just as some few still
living organic beings belong to Silurian genera. So that the amount or
value of the differences between organic beings all related to each
other in the same degree in blood, has come to be widely different.
Nevertheless their genealogical ARRANGEMENT remains strictly true, not
only at the present time, but at each successive period of descent.
All the modified descendants from A will have inherited something in
common from their common parent, as will all the descendants from I;
so will it be with each subordinate branch of descendants, at each
successive period. If, however, we choose to suppose that any of the
descendants of A or of I have been so much modified as to have more or
less completely lost traces of their parentage, in this case, their
places in a natural classification will have been more or less
completely lost,--as sometimes seems to have occurred with existing
organisms. All the descendants of the genus F, along its whole line of
descent, are supposed to have been but little modified, and they yet
form a single genus. But this genus, though much isolated, will still
occupy its proper intermediate position; for F originally was
intermediate in character between A and I, and the several genera
descended from these two genera will have inherited to a certain
extent their characters. This natural arrangement is shown, as far as
is possible on paper, in the diagram, but in much too simple a manner.
If a branching diagram had not been used, and only the names of the
groups had been written in a linear series, it would have been still
less possible to have given a natural arrangement; and it is
notoriously not possible to represent in a series, on a flat surface,
the affinities which we discover in nature amongst the beings of the
same group. Thus, on the view which I hold, the natural system is
genealogical in its arrangement, like a pedigree; but the degrees of
modification which the different groups have undergone, have to be
expressed by ranking them under different so-called genera,
sub-families, families, sections, orders, and classes.

It may be worth while to illustrate this view of classification, by
taking the case of languages. If we possessed a perfect pedigree of
mankind, a genealogical arrangement of the races of man would afford
the best classification of the various languages now spoken throughout
the world; and if all extinct languages, and all intermediate and
slowly changing dialects, had to be included, such an arrangement
would, I think, be the only possible one. Yet it might be that some
very ancient language had altered little, and had given rise to few
new languages, whilst others (owing to the spreading and subsequent
isolation and states of civilisation of the several races, descended
from a common race) had altered much, and had given rise to many new
languages and dialects. The various degrees of difference in the
languages from the same stock, would have to be expressed by groups
subordinate to groups; but the proper or even only possible
arrangement would still be genealogical; and this would be strictly
natural, as it would connect together all languages, extinct and
modern, by the closest affinities, and would give the filiation and
origin of each tongue.

In confirmation of this view, let us glance at the classification of
varieties, which are believed or known to have descended from one
species. These are grouped under species, with sub-varieties under
varieties; and with our domestic productions, several other grades of
difference are requisite, as we have seen with pigeons. The origin of
the existence of groups subordinate to groups, is the same with
varieties as with species, namely, closeness of descent with various
degrees of modification. Nearly the same rules are followed in
classifying varieties, as with species. Authors have insisted on the
necessity of classing varieties on a natural instead of an artificial
system; we are cautioned, for instance, not to class two varieties of
the pine-apple together, merely because their fruit, though the most
important part, happens to be nearly identical; no one puts the
swedish and common turnips together, though the esculent and thickened
stems are so similar. Whatever part is found to be most constant, is
used in classing varieties: thus the great agriculturist Marshall says
the horns are very useful for this purpose with cattle, because they
are less variable than the shape or colour of the body, etc.; whereas
with sheep the horns are much less serviceable, because less constant.
In classing varieties, I apprehend if we had a real pedigree, a
genealogical classification would be universally preferred; and it has
been attempted by some authors. For we might feel sure, whether there
had been more or less modification, the principle of inheritance would
keep the forms together which were allied in the greatest number of
points. In tumbler pigeons, though some sub-varieties differ from the
others in the important character of having a longer beak, yet all are
kept together from having the common habit of tumbling; but the
short-faced breed has nearly or quite lost this habit; nevertheless,
without any reasoning or thinking on the subject, these tumblers are
kept in the same group, because allied in blood and alike in some
other respects. If it could be proved that the Hottentot had descended
from the Negro, I think he would be classed under the Negro group,
however much he might differ in colour and other important characters
from negroes.

With species in a state of nature, every naturalist has in fact
brought descent into his classification; for he includes in his lowest
grade, or that of a species, the two sexes; and how enormously these
sometimes differ in the most important characters, is known to every
naturalist: scarcely a single fact can be predicated in common of the
males and hermaphrodites of certain cirripedes, when adult, and yet no
one dreams of separating them. The naturalist includes as one species
the several larval stages of the same individual, however much they
may differ from each other and from the adult; as he likewise includes
the so-called alternate generations of Steenstrup, which can only in a
technical sense be considered as the same individual. He includes
monsters; he includes varieties, not solely because they closely
resemble the parent-form, but because they are descended from it. He
who believes that the cowslip is descended from the primrose, or
conversely, ranks them together as a single species, and gives a
single definition. As soon as three Orchidean forms (Monochanthus,
Myanthus, and Catasetum), which had previously been ranked as three
distinct genera, were known to be sometimes produced on the same
spike, they were immediately included as a single species. But it may
be asked, what ought we to do, if it could be proved that one species
of kangaroo had been produced, by a long course of modification, from
a bear? Ought we to rank this one species with bears, and what should
we do with the other species? The supposition is of course
preposterous; and I might answer by the argumentum ad hominem, and ask
what should be done if a perfect kangaroo were seen to come out of the
womb of a bear? According to all analogy, it would be ranked with
bears; but then assuredly all the other species of the kangaroo family
would have to be classed under the bear genus. The whole case is
preposterous; for where there has been close descent in common, there
will certainly be close resemblance or affinity.

As descent has universally been used in classing together the
individuals of the same species, though the males and females and
larvae are sometimes extremely different; and as it has been used in
classing varieties which have undergone a certain, and sometimes a
considerable amount of modification, may not this same element of
descent have been unconsciously used in grouping species under genera,
and genera under higher groups, though in these cases the modification
has been greater in degree, and has taken a longer time to complete? I
believe it has thus been unconsciously used; and only thus can I
understand the several rules and guides which have been followed by
our best systematists. We have no written pedigrees; we have to make
out community of descent by resemblances of any kind. Therefore we
choose those characters which, as far as we can judge, are the least
likely to have been modified in relation to the conditions of life to
which each species has been recently exposed. Rudimentary structures
on this view are as good as, or even sometimes better than, other
parts of the organisation. We care not how trifling a character may
be--let it be the mere inflection of the angle of the jaw, the manner
in which an insect's wing is folded, whether the skin be covered by
hair or feathers--if it prevail throughout many and different species,
especially those having very different habits of life, it assumes high
value; for we can account for its presence in so many forms with such
different habits, only by its inheritance from a common parent. We may
err in this respect in regard to single points of structure, but when
several characters, let them be ever so trifling, occur together
throughout a large group of beings having different habits, we may
feel almost sure, on the theory of descent, that these characters have
been inherited from a common ancestor. And we know that such
correlated or aggregated characters have especial value in
classification.

We can understand why a species or a group of species may depart, in
several of its most important characteristics, from its allies, and
yet be safely classed with them. This may be safely done, and is often
done, as long as a sufficient number of characters, let them be ever
so unimportant, betrays the hidden bond of community of descent. Let
two forms have not a single character in common, yet if these extreme
forms are connected together by a chain of intermediate groups, we may
at once infer their community of descent, and we put them all into the
same class. As we find organs of high physiological importance--those
which serve to preserve life under the most diverse conditions of
existence--are generally the most constant, we attach especial value
to them; but if these same organs, in another group or section of a
group, are found to differ much, we at once value them less in our
classification. We shall hereafter, I think, clearly see why
embryological characters are of such high classificatory importance.
Geographical distribution may sometimes be brought usefully into play
in classing large and widely-distributed genera, because all the
species of the same genus, inhabiting any distinct and isolated
region, have in all probability descended from the same parents.

We can understand, on these views, the very important distinction
between real affinities and analogical or adaptive resemblances.
Lamarck first called attention to this distinction, and he has been
ably followed by Macleay and others. The resemblance, in the shape of
the body and in the fin-like anterior limbs, between the dugong, which
is a pachydermatous animal, and the whale, and between both these
mammals and fishes, is analogical. Amongst insects there are
innumerable instances: thus Linnaeus, misled by external appearances,
actually classed an homopterous insect as a moth. We see something of
the same kind even in our domestic varieties, as in the thickened
stems of the common and swedish turnip. The resemblance of the
greyhound and racehorse is hardly more fanciful than the analogies
which have been drawn by some authors between very distinct animals.
On my view of characters being of real importance for classification,
only in so far as they reveal descent, we can clearly understand why
analogical or adaptive character, although of the utmost importance to
the welfare of the being, are almost valueless to the systematist. For
animals, belonging to two most distinct lines of descent, may readily
become adapted to similar conditions, and thus assume a close external
resemblance; but such resemblances will not reveal--will rather tend
to conceal their blood-relationship to their proper lines of descent.
We can also understand the apparent paradox, that the very same
characters are analogical when one class or order is compared with
another, but give true affinities when the members of the same class
or order are compared one with another: thus the shape of the body and
fin-like limbs are only analogical when whales are compared with
fishes, being adaptations in both classes for swimming through the
water; but the shape of the body and fin-like limbs serve as
characters exhibiting true affinity between the several members of the
whale family; for these cetaceans agree in so many characters, great
and small, that we cannot doubt that they have inherited their general
shape of body and structure of limbs from a common ancestor. So it is
with fishes.

As members of distinct classes have often been adapted by successive
slight modifications to live under nearly similar circumstances,--to
inhabit for instance the three elements of land, air, and water,--we
can perhaps understand how it is that a numerical parallelism has
sometimes been observed between the sub-groups in distinct classes. A
naturalist, struck by a parallelism of this nature in any one class,
by arbitrarily raising or sinking the value of the groups in other
classes (and all our experience shows that this valuation has hitherto
been arbitrary), could easily extend the parallelism over a wide
range; and thus the septenary, quinary, quaternary, and ternary
classifications have probably arisen.

As the modified descendants of dominant species, belonging to the
larger genera, tend to inherit the advantages, which made the groups
to which they belong large and their parents dominant, they are almost
sure to spread widely, and to seize on more and more places in the
economy of nature. The larger and more dominant groups thus tend to go
on increasing in size; and they consequently supplant many smaller and
feebler groups. Thus we can account for the fact that all organisms,
recent and extinct, are included under a few great orders, under still
fewer classes, and all in one great natural system. As showing how few
the higher groups are in number, and how widely spread they are
throughout the world, the fact is striking, that the discovery of
Australia has not added a single insect belonging to a new order; and
that in the vegetable kingdom, as I learn from Dr. Hooker, it has
added only two or three orders of small size.

In the chapter on geological succession I attempted to show, on the
principle of each group having generally diverged much in character
during the long-continued process of modification, how it is that the
more ancient forms of life often present characters in some slight
degree intermediate between existing groups. A few old and
intermediate parent-forms having occasionally transmitted to the
present day descendants but little modified, will give to us our
so-called osculant or aberrant groups. The more aberrant any form is,
the greater must be the number of connecting forms which on my theory
have been exterminated and utterly lost. And we have some evidence of
aberrant forms having suffered severely from extinction, for they are
generally represented by extremely few species; and such species as do
occur are generally very distinct from each other, which again implies
extinction. The genera Ornithorhynchus and Lepidosiren, for example,
would not have been less aberrant had each been represented by a dozen
species instead of by a single one; but such richness in species, as I
find after some investigation, does not commonly fall to the lot of
aberrant genera. We can, I think, account for this fact only by
looking at aberrant forms as failing groups conquered by more
successful competitors, with a few members preserved by some unusual
coincidence of favourable circumstances.

Mr. Waterhouse has remarked that, when a member belonging to one group
of animals exhibits an affinity to a quite distinct group, this
affinity in most cases is general and not special: thus, according to
Mr. Waterhouse, of all Rodents, the bizcacha is most nearly related to
Marsupials; but in the points in which it approaches this order, its
relations are general, and not to any one marsupial species more than
to another. As the points of affinity of the bizcacha to Marsupials
are believed to be real and not merely adaptive, they are due on my
theory to inheritance in common. Therefore we must suppose either that
all Rodents, including the bizcacha, branched off from some very
ancient Marsupial, which will have had a character in some degree
intermediate with respect to all existing Marsupials; or that both
Rodents and Marsupials branched off from a common progenitor, and that
both groups have since undergone much modification in divergent
directions. On either view we may suppose that the bizcacha has
retained, by inheritance, more of the character of its ancient
progenitor than have other Rodents; and therefore it will not be
specially related to any one existing Marsupial, but indirectly to all
or nearly all Marsupials, from having partially retained the character
of their common progenitor, or of an early member of the group. On the
other hand, of all Marsupials, as Mr. Waterhouse has remarked, the
phascolomys resembles most nearly, not any one species, but the
general order of Rodents. In this case, however, it may be strongly
suspected that the resemblance is only analogical, owing to the
phascolomys having become adapted to habits like those of a Rodent.
The elder De Candolle has made nearly similar observations on the
general nature of the affinities of distinct orders of plants.

On the principle of the multiplication and gradual divergence in
character of the species descended from a common parent, together with
their retention by inheritance of some characters in common, we can
understand the excessively complex and radiating affinities by which
all the members of the same family or higher group are connected
together. For the common parent of a whole family of species, now
broken up by extinction into distinct groups and sub-groups, will have
transmitted some of its characters, modified in various ways and
degrees, to all; and the several species will consequently be related
to each other by circuitous lines of affinity of various lengths (as
may be seen in the diagram so often referred to), mounting up through
many predecessors. As it is difficult to show the blood-relationship
between the numerous kindred of any ancient and noble family, even by
the aid of a genealogical tree, and almost impossible to do this
without this aid, we can understand the extraordinary difficulty which
naturalists have experienced in describing, without the aid of a
diagram, the various affinities which they perceive between the many
living and extinct members of the same great natural class.