pure Ancons, or pure ordinary sheep.* But when sufficient Ancon sheep
were obtained to interbreed with one another, it was found that the
offspring was always pure Ancon. Colonel Humphreys, in fact, states
that he was acquainted with only "one questionable case of a contrary
nature." Here, then, is a remarkable and well-established instance,
not only of a very distinct race being established 'per saltum', but of
that race breeding "true" at once, and showing no mixed forms, even
when crossed with another breed.
[footnote] *Colonel Humphreys' statements are exceedingly
explicit on this point: - "When an Ancon ewe is impregnated
by a common ram, the increase resembles wholly either the
ewe or the ram. The increase of the common ewe impregnated
by an Ancon ram follows entirely the one or the other,
without blending any of the distinguishing and essential
peculiarities of both. Frequent instances have happened
where common ewes have had twins by Ancon rams, when one
exhibited the complete marks and features of the ewe, the
other of the ram. The contrast has been rendered
singularly striking, when one short-legged and one
long-legged lamb, produced at a birth, have been seen
sucking the dam at the same time." - 'Philosophical
Transactions', 1813, Pt. I. pp. 89, 90.
By taking care to select Ancons of both sexes, for breeding from, it
thus became easy to establish an extremely well-marked race; so
peculiar that, even when herded with other sheep, it was noted that the
Ancons kept together. And there is every reason to believe that the
existence of this breed might have been indefinitely protracted; but the
introduction of the Merino sheep, which were not only very superior to
the Ancons in wool and meat, but quite as quiet and orderly, led to the
complete neglect of the new breed, so that, in 1813, Colonel Humphreys
found it difficult to obtain the specimen, whose skeleton was presented
to Sir Joseph Banks. We believe that, for many years, no remnant of it
has existed in the United States.
Gratio Kelleia was not the progenitor of a race of six-fingered men, as
Seth Wright's ram became a nation of Ancon sheep, though the tendency
of the variety to perpetuate itself appears to have been fully as
strong in the one case as in the other. And the reason of the
difference is not far to seek. Seth Wright took care not to weaken the
Ancon blood by matching his Ancon ewes with any but males of the same
variety, while Gratio Kelleia's sons were too far removed from the
patriarchal times to intermarry with their sisters; and his
grandchildren seem not to have been attracted by their six-fingered
cousins. In other words, in the one example a race was produced,
because, for several generations, care was taken to 'select' both
parents of the breeding stock from animals exhibiting a tendency to vary
in the same condition; while, in the other, no race was evolved,
because no such selection was exercised. A race is a propagated
variety; and as, by the laws of reproduction, offspring tend to assume
the parental forms, they will be more likely to propagate a variation
exhibited by both parents than that possessed by only one.
There is no organ of the body of an animal which may not, and does not,
occasionally, vary more or less from the normal type; and there is no
variation which may not be transmitted and which, if selectively
transmitted, may not become the foundation of a race. This great
truth, sometimes forgotten by philosophers, has long been familiar to
practical agriculturists and breeders; and upon it rest all the methods
of improving the breeds of domestic animals, which, for the last
century, have been followed with so much success in England. Colour,
form, size, texture of hair or wool, proportions of various parts,
strength or weakness of constitution, tendency to fatten or to remain
lean, to give much or little milk, speed, strength, temper,
intelligence, special instincts; there is not one of these characters
whose transmission is not an every-day occurrence within the experience
of cattle-breeders, stock-farmers, horse-dealers, and dog and poultry
fanciers. Nay, it is only the other day that an eminent physiologist,
Dr. Brown-Sequard, communicated to the Royal Society his discovery
that epilepsy, artificially produced in guinea-pigs, by a means which
he has discovered, is transmitted to their offspring.
But a race, once produced, is no more a fixed and immutable entity than
the stock whence it sprang; variations arise among its members, and as
these variations are transmitted like any others, new races may be
developed out of the pre-existing one 'ad infinitum', or, at least,
within any limit at present determined. Given sufficient time and
sufficiently careful selection, and the multitude of races which may
arise from a common stock is as astonishing as are the extreme
structural differences which they may present. A remarkable example of
this is to be found in the rock-pigeon, which Dr. Darwin has, in our
opinion, satisfactorily demonstrated to be the progenitor of all our
domestic pigeons, of which there are certainly more than a hundred
well-marked races. The most noteworthy of these races are, the four
great stocks known to the "fancy" as tumblers, pouters, carriers, and
fantails; birds which not only differ most singularly in size, colour,
and habits, but in the form of the beak and of the skull: in the
proportions of the beak to the skull; in the number of tail-feathers;
in the absolute and relative size of the feet; in the presence or
absence of the uropygial gland; in the number of vertebrae in the back;
in short, in precisely those characters in which the genera and species
of birds differ from one another.
And it is most remarkable and instructive to observe, that none of these
races can be shown to have been originated by the action of changes in
what are commonly called external circumstances, upon the wild
rock-pigeon. On the contrary, from time immemorial, pigeon-fanciers
have had essentially similar methods of treating their pets, which have
been housed, fed, protected and cared for in much the same way in all
pigeonries. In fact, there is no case better adapted than that of the
pigeons to refute the doctrine which one sees put forth on high
authority, that "no other characters than those founded on the
development of bone for the attachment of muscles" are capable of
variation. In precise contradiction of this hasty assertion, Mr.
Darwin's researches prove that the skeleton of the wings in domestic
pigeons has hardly varied at all from that of the wild type; while, on
the other hand, it is in exactly those respects, such as the relative
length of the beak and skull, the number of the vertebrae, and the
number of the tail-feathers, in which muscular exertion can have no
important influence, that the utmost amount of variation has taken
place.
We have said that the following out of the properties exhibited by
physiological species would lead us into difficulties, and at this
point they begin to be obvious; for if, as the result of spontaneous
variation and of selective breeding, the progeny of a common stock may
become separated into groups distinguished from one another by
constant, not sexual, morphological characters, it is clear that the
physiological definition of species is likely to clash with the
morphological definition. No one would hesitate to describe the pouter
and the tumbler as distinct species, if they were found fossil, or if
their skins and skeletons were imported, as those of exotic wild birds
commonly are - and without doubt, if considered alone, they are good and
distinct morphological species. On the other hand, they are not
physiological species, for they are descended from a common stock, the
rock-pigeon.
Under these circumstances, as it is admitted on all sides that races
occur in Nature, how are we to know whether any apparently distinct
animals are really of different physiological species, or not, seeing
that the amount of morphological difference is no safe guide? Is there
any test of a physiological species? The usual answer of physiologists
is in the affirmative. It is said that such a test is to be found in
the phenomena of hybridization - in the results of crossing races, as
compared with the results of crossing species.
So far as the evidence goes at present, individuals, of what are
certainly known to be mere races produced by selection, however
distinct they may appear to be, not only breed freely together, but the
offspring of such crossed races are only perfectly fertile with one
another. Thus, the spaniel and the greyhound, the dray-horse and the
Arab, the pouter and the tumbler, breed together with perfect freedom,
and their mongrels, if matched with other mongrels of the same kind,
are equally fertile.
On the other hand, there can be no doubt that the individuals of many
natural species are either absolutely infertile if crossed with
individuals of other species, or, if they give rise to hybrid
offspring, the hybrids so produced are infertile when paired together.
The horse and the ass, for instance, if so crossed, give rise to the
mule, and there is no certain evidence of offspring ever having been
produced by a male and female mule. The unions of the rock-pigeon and
the ring-pigeon appear to be equally barren of result. Here, then,
says the physiologist, we have a means of distinguishing any two true
species from any two varieties. If a male and a female, selected from
each group, produce offspring, and that offspring is fertile with others
produced in the same way, the groups are races and not species. If, on
the other hand, no result ensues, or if the offspring are infertile
with others produced in the same way, they are true physiological
species. The test would be an admirable one, if, in the first place, it
were always practicable to apply it, and if, in the second, it always
yielded results susceptible of a definite interpretation.
Unfortunately, in the great majority of cases, this touchstone for
species is wholly inapplicable.
The constitution of many wild animals is so altered by confinement that
they will not breed even with their own females, so that the negative
results obtained from crosses are of no value; and the antipathy of
wild animals of the same species for one another, or even of wild and
tame members of the same species, is ordinarily so great, that it is
hopeless to look for such unions in Nature. The hermaphrodism of most
plants, the difficulty in the way of insuring the absence of their own,
or the proper working of other pollen, are obstacles of no less
magnitude in applying the test to them. And, in both animals and
plants, is superadded the further difficulty, that experiments must be
continued over a long time for the purpose of ascertaining the
fertility of the mongrel or hybrid progeny, as well as of the first
crosses from which they spring.
Not only do these great practical difficulties lie in the way of
applying the hybridization test, but even when this oracle can be
questioned, its replies are sometimes as doubtful as those of Delphi.
For example, cases are cited by Mr. Darwin, of plants which are more
fertile with the pollen of another species than with their own; and
there are others, such as certain 'fuci', whose male element will
fertilize the ovule of a plant of distinct species, while the males of
the latter species are ineffective with the females of the first. So
that, in the last-named instance, a physiologist, who should cross the
two species in one way, would decide that they were true species; while
another, who should cross them in the reverse way, would, with equal
justice, according to the rule, pronounce them to be mere races.
Several plants, which there is great reason to believe are mere
varieties, are almost sterile when crossed; while both animals and
plants, which have always been regarded by naturalists as of distinct
species, turn out, when the test is applied, to be perfectly fertile.
Again, the sterility or fertility of crosses seems to bear no relation
to the structural resemblances or differences of the members of any two
groups.
Mr. Darwin has discussed this question with singular ability and
circumspection, and his conclusions are summed up as follows, at page
276 of his work: -
"First crosses between forms sufficiently distinct to be ranked as
species, and their hybrids, are very generally, but not universally,
sterile. The sterility is of all degrees, and is often so slight that
the two most careful experimentalists who have ever lived have come to
diametrically opposite conclusions in ranking forms by this test. The
sterility is innately variable in individuals of the same species, and
is eminently susceptible of favourable and unfavourable conditions. The
degree of sterility does not strictly follow systematic affinity, but is
governed by several curious and complex laws. It is generally
different and sometimes widely different, in reciprocal crosses between
the same two species. It is not always equal in degree in a first
cross, and in the hybrid produced from this cross.
"In the same manner as in grafting trees, the capacity of one species or
variety to take on another is incidental on generally unknown
differences in their vegetative systems; so in crossing, the greater or
less facility of one species to unite with another is incidental on
unknown differences in their reproductive systems. There is no more
reason to think that species have been specially endowed with various
degrees of sterility to prevent them crossing and breeding in Nature,
than to think that trees have been specially endowed with various and
somewhat analogous degrees of difficulty in being grafted together, in
order to prevent them becoming inarched in our forests.
"The sterility of first crosses between pure species, which have their
reproductive systems perfect, seems to depend on several circumstances;
in some cases largely on the early death of the embryo. The sterility
of hybrids which have their reproductive systems imperfect, and which
have had this system and their whole organization disturbed by being
compounded of two distinct species, seems closely allied to that
sterility which so frequently affects pure species when their natural
conditions of life have been disturbed. This view is supported by a
parallelism of another kind: namely, that the crossing of forms, only
slightly different, is favourable to the vigour and fertility of the
offspring; and that slight changes in the conditions of life are
apparently favourable to the vigour and fertility of all organic beings.
It is not surprising that the degree of difficulty in uniting two
species, and the degree of sterility of their hybrid offspring, should
generally correspond, though due to distinct causes; for both depend on
the amount of difference of some kind between the species which are
crossed. Nor is it surprising that the facility of effecting a first
cross, the fertility of hybrids produced from it, and the capacity of
being grafted together - though this latter capacity evidently depends
on widely different circumstances - should all run to a certain extent
parallel with the systematic affinity of the forms which are subjected
to experiment; for systematic affinity attempts to express all kinds of
resemblance between all species.
"First crosses between forms known to be varieties, or sufficiently
alike to be considered as varieties, and their mongrel offspring, are
very generally, but not quite universally, fertile. Nor is this nearly
general and perfect fertility surprising, when we remember how liable we
are to argue in a circle with respect to varieties in a state of
Nature; and when we remember that the greater number of varieties have
been produced under domestication by the selection of mere external
differences, and not of differences in the reproductive system. In all
other respects, excluding fertility, there is a close general
resemblance between hybrids and mongrels." - Pp. 276-8.
We fully agree with the general tenor of this weighty passage; but
forcible as are these arguments, and little as the value of fertility
or infertility as a test of species may be, it must not be forgotten
that the really important fact, so far as the inquiry into the origin of
species goes, is, that there are such things in Nature as groups of
animals and of plants, whose members are incapable of fertile union
with those of other groups; and that there are such things as hybrids,
which are absolutely sterile when crossed with other hybrids. For, if
such phenomena as these were exhibited by only two of those assemblages
of living objects, to which the name of species (whether it be used in
its physiological or in its morphological sense) is given, it would
have to be accounted for by any theory of the origin of species, and
every theory which could not account for it would be, so far,
imperfect.
Up to this point, we have been dealing with matters of fact, and the
statements which we have laid before the reader would, to the best of
our knowledge, be admitted to contain a fair exposition of what is at
present known respecting the essential properties of species, by all
who have studied the question. And whatever may be his theoretical
views, no naturalist will probably be disposed to demur to the
following summary of that exposition: -
Living beings, whether animals or plants, are divisible into multitudes
of distinctly definable kinds, which are morphological species. They
are also divisible into groups of individuals, which breed freely
together, tending to reproduce their like, and are physiological
species. Normally resembling their parents, the offspring of members of
these species are still liable to vary; and the variation may be
perpetuated by selection, as a race, which race, in many cases,
presents all the characteristics of a morphological species. But it is
not as yet proved that a race ever exhibits, when crossed with another
race of the same species, those phenomena of hybridization which are
exhibited by many species when crossed with other species. On the
other hand, not only is it not proved that all species give rise to
hybrids infertile 'inter se', but there is much reason to believe that,
in crossing, species exhibit every gradation from perfect sterility to
perfect fertility.
Such are the most essential characteristics of species. Even were man
not one of them - a member of the same system and subject to the same
laws - the question of their origin, their causal connexion, that is,
with the other phenomena of the universe, must have attracted his
attention, as soon as his intelligence had raised itself above the level
of his daily wants.
Indeed history relates that such was the case, and has embalmed for us
the speculations upon the origin of living beings, which were among the
earliest products of the dawning intellectual activity of man. In
those early days positive knowledge was not to be had, but the craving
after it needed, at all hazards, to be satisfied, and according to the
country, or the turn of thought, of the speculator, the suggestion that
all living things arose from the mud of the Nile, from a primeval egg,
or from some more anthropomorphic agency, afforded a sufficient
resting-place for his curiosity. The myths of Paganism are as dead as
Osiris or Zeus, and the man who should revive them, in opposition to
the knowledge of our time, would be justly laughed to scorn; but the
coeval imaginations current among the rude inhabitants of Palestine,
recorded by writers whose very name and age are admitted by every
scholar to be unknown, have unfortunately not yet shared their fate,
but, even at this day, are regarded by nine-tenths of the civilized
world as the authoritative standard of fact and the criterion of the
justice of scientific conclusions, in all that relates to the origin of
things, and, among them, of species. In this nineteenth century, as at
the dawn of modern physical science, the cosmogony of the
semi-barbarous Hebrew is the incubus of the philosopher and the
opprobrium of the orthodox. Who shall number the patient and earnest
seekers after truth, from the days of Galileo until now, whose lives
have been embittered and their good name blasted by the mistaken zeal
of Bibliolaters? Who shall count the host of weaker men whose sense of
truth has been destroyed in the effort to harmonize
impossibilities - whose life has been wasted in the attempt to force the
generous new wine of Science into the old bottles of Judaism, compelled
by the outcry of the same strong party?
It is true that if philosophers have suffered, their cause has been
amply avenged. Extinguished theologians lie about the cradle of every
science as the strangled snakes beside that of Hercules; and history
records that whenever science and orthodoxy have been fairly opposed,
the latter has been forced to retire from the lists, bleeding and
crushed if not annihilated; scotched, if not slain. But orthodoxy is
the Bourbon of the world of thought. It learns not, neither can it
forget; and though, at present, bewildered and afraid to move, it is as
willing as ever to insist that the first chapter of Genesis contains
the beginning and the end of sound science; and to visit, with such
petty thunderbolts as its half-paralysed hands can hurl, those who
refuse to degrade Nature to the level of primitive Judaism.
Philosophers, on the other hand, have no such aggressive tendencies.
With eyes fixed on the noble goal to which "per aspera et ardua" they
tend, they may, now and then, be stirred to momentary wrath by the
unnecessary obstacles with which the ignorant, or the malicious,
encumber, if they cannot bar, the difficult path; but why should their
souls be deeply vexed? The majesty of Fact is on their side, and the
elemental forces of Nature are working for them. Not a star comes to
the meridian at its calculated time but testifies to the justice of
their methods - their beliefs are "one with falling rain and with the
growing corn." By doubt they are established, and open inquiry is
their bosom friend. Such men have no fear of traditions however
venerable, and no respect for them when they become mischievous and
obstructive; but they have better than mere antiquarian business in
hand, and if dogmas, which ought to be fossil but are not, are not
forced upon their notice, they are too happy to treat them as
non-existent.
The hypotheses respecting the origin of species which profess to stand
upon a scientific basis, and, as such, alone demand serious attention,
are of two kinds. The one, the "special creation" hypothesis, presumes
every species to have originated from one or more stocks, these not
being the result of the modification of any other form of living
matter - or arising by natural agencies - but being produced, as such, by
a supernatural creative act.
The other, the so-called "transmutation" hypothesis, considers that all
existing species are the result of the modification of pre-existing
species, and those of their predecessors, by agencies similar to those
which at the present day produce varieties and races, and therefore in
an altogether natural way; and it is a probable, though not a necessary
consequence of this hypothesis, that all living beings have arisen from
a single stock. With respect to the origin of this primitive stock, or
stocks, the doctrine of the origin of species is obviously not
necessarily concerned. The transmutation hypothesis, for example, is
perfectly consistent either with the conception of a special creation
of the primitive germ, or with the supposition of its having arisen, as
a modification of inorganic matter, by natural causes.
The doctrine of special creation owes its existence very largely to the
supposed necessity of making science accord with the Hebrew cosmogony;
but it is curious to observe that, as the doctrine is at present
maintained by men of science, it is as hopelessly inconsistent with the
Hebrew view as any other hypothesis.
If there be any result which has come more clearly out of geological
investigation than another, it is, that the vast series of extinct
animals and plants is not divisible, as it was once supposed to be,
into distinct groups, separated by sharply-marked boundaries. There are
no great gulfs between epochs and formations - no successive periods
marked by the appearance of plants, of water animals, and of land