CROSSING BETWEEN VEGETABLE AND ANIMAL RACES AND SPECIES; MONGRELS AND
HYBRIDS; REALITY OF SPECIES.
I. From the very first, in the union of two individuals belonging
to different stocks, the race and the species display very distinct
and characteristic phenomena. We shall now see this opposition as
strongly marked in the product of these unions in _mongrels_ and
_hybrids_.
Several questions are raised by the mixed nature of these beings.
I shall confine myself to those which refer to filiation, and
which have therefore a special interest for us. They may be stated
generally as follows:—are _mongrel races_, that is, those derived
from _two_ distinct _races_, and _hybrid races_, that is those which
are derived from the crossing of _two species_, formed naturally,
or can they be obtained artificially? In other words, do mongrels
and hybrids retain, during an indefinite number of generations, the
faculty of reproducing and transmitting to their descendants the
mixed character they inherited from the first parents which effected
the cross?
II. In regard to mongrels there is not a shadow of doubt. Facts which
frequently occur, often without our intervention, and sometimes in
spite of our precautions, prove again and again that the mongrels
of the first generation are as fertile as the parents, and transmit
equal fertility to their offspring. Our gardeners and breeders always
take advantage of this property of mongrels in order to vary, modify
or ameliorate from their point of view the plants and animals in
which they are interested; the careful experiments of Buffon, of
Geoffroy St.-Hilaire, father and son, and the testimony of Darwin,
on this point very significant, prove beyond a doubt that unions
between different races remain fertile, whatever morphological
differences there may be between them. I shall confine myself to
quoting one example from Darwin. The niata will unite indifferently
in both senses with the ordinary ox, and the offspring is fertile.
If several races of a single species are in habitual contact and left
to themselves, they will intermix in every degree. This results in
bastard offspring, devoid of definite characters, but which, when
methodically studied, would lead through _insensible shades_ to the
different primitive types. In this manner our street dogs and cats
have come into existence, which remain perfectly fertile in spite of
innumerable crossings of every kind.
With human intervention it is possible, when care is taken, to
regulate the crossing between two races, and to obtain a mongrel
race. After a few oscillations between the paternal and maternal
types it becomes consolidated and settled. But whatever constancy
it may have acquired as a whole, it almost always happens that some
individuals reproduce, to a varying extent, the characters of one of
the types originally crossed.
This phenomenon is designated by the name of _Atavism_. It sometimes
occurs in the midst of a race considered to be perfectly pure, and
is the result of a single crossing several generations back. Darwin
quotes the case of a breeder, who having crossed his fowls with the
Malay race, wished afterwards to free them from the strange blood.
After spending forty years in the attempt, he is still unsuccessful,
the Malay blood always reappearing in some of his fowls.
In animals as in plants, universal, free and indefinite fertility,
whether between themselves or between all the races of the same
species, is one of the characters of mongrels. Atavism attests the
physiological bond which unites all mongrels.
III. In hybrids we shall meet with some very different phenomena.
Let us first, with M. Godron, establish the fact that in the
vegetable hybrid the physiological equilibrium is destroyed in favour
of the organs conducive to the life of the individual, and at the
expense of those conducive to the life of the species. The stalk and
leaves are always developed in an exaggerated manner relatively to
the flowers. The most common animal hybrid, the mule, is an entirely
similar case, being invariably stronger, more robust, more hardy than
its parents, but sterile.
This sterility is not absolute, however, among all hybrids of the
first generation. It generally affects the male organs in an entirely
special manner. Koelreuter, to whom we should always refer when
treating of plants, states that the anthers scarcely ever enclose
veritable pollen, but merely irregular granulations. It was not quite
so unusual to find ovules in good condition in the ovary. Guided by
these observations, Koelreuter artificially fertilised hybrid flowers
with pollen from the male species, and thus obtained a _vegetable
quadroon_. By continuing this process he soon brought back again to
the original male type the descendants of the first hybrid, which
regained all their generative faculties, but at the same time lost
all trace of the female type. These experiments have been repeated
and varied, but always with the same result.
In a small number of hybrids of the first generation the elements
which characterise the two sexes remained capable of reproduction.
Nevertheless the fertility is always immensely reduced. From his
hybrids of the datura, M. Naudin only obtained five or six fertile
seeds from each plant. All the others had completely failed, or were
without an embryo. The capsules themselves were only half the normal
size.
If two of these first hybrids are united they produce hybrids of the
second generation. In most cases, however, the latter are either
sterile, or present the phenomenon of a _spontaneous return_ to one
or the other of the parent types, or to both. M. Naudin crossed the
_large-leaved primrose_ with the _primula officinalis_, and obtained
an intermediate hybrid between the two species, having seven fertile
seeds. When these were sown they produced three primroses of the male
species, three of the female, and a single hybrid plant which was
perfectly barren.
In some still rarer cases fertility continues during several
generations. Then, however, a curious phenomenon is exhibited,
called by M. Naudin, who discovered it, _Disordered variation._ With
the _Linaria communis_ and the _Linaria purpurea_ he produced a
hybrid, the descendants of which he was able to follow through seven
generations, in each of which several individuals reverted to the
characters either of the original male or female. The others neither
resembled the primitive types nor the hybrid resulting from their
crossing, nor the plants of which they were the immediate offspring,
nor was there any resemblance between the plants themselves.
Thus the crossing does not produce a race, even in cases where it
allows a certain amount of fertility; it only produces _varieties_
incapable of transmitting their individual characters. In order to
establish a series of generations presenting a certain amount of
uniformity, the hybrid must lose some of its mixed characters, and
resume the normal livery of the species, as M. Naudin says; in other
words, it must return to one of the parent types.
IV. The same facts which we have just noticed among plants, occur
also among animals. We must observe in the first place, that the only
two species, the crossing of which displays anything approaching to
regular fertility, the horse and the ass, merely produce a hybrid
almost entirely devoid of fertility. It is more than 2000 years since
Herodotus regarded the fertility of mules as a prodigy, and almost
1800 years since Pliny expressed the same opinion.
And yet in some works we read that the fertility of the mule is
displayed in the present day; that it often propagates in hot
countries, especially in Algeria. The true value of these singular
assertions will be recognised if we recall the effect which was
produced in 1828 upon the whole Mussulman population of Algeria
by the announcement that a mule had conceived near Biskra. The
astonishment was general; the Arabs gave themselves up to long fasts
to conciliate the wrath of heaven, thinking the end of the world had
come. Fortunately the mule miscarried; but long afterwards the Arabs
still spoke with terror of this event.
If this fact were occasionally repeated in Algeria it would never
have produced such an impression upon a people so curious about
everything connected with the horse. The impression itself proves
that the facts are in our days similar to what they were in the time
of Herodotus.
Examples of fertility in the hybrids of the ass and the horse have
never been observed except in the _female mule_. There is not a
single known example in the _male_. We meet with something analogous
to this in birds, where the sterility of certain hybrids is less
absolute. Thus vertebrata are similarly affected with plants; and
in their case also the inequality between the two sexes can be
explained by anatomical and microscopic examination. The male organs
are generally but slightly developed, even the essential elements
of the fertilising liquid undergo alteration. The female organs and
elements, though modified, are relatively unaffected.
There are some hybrids among animals, as among plants, which are not
subject to the general law. Among birds in particular, a certain
number, always however very limited, of more or less fertile hybrids
have been obtained. But, with the males the faculty of reproduction
is constantly weakened, and habitually disappears before the usual
age; the female lays more rarely, and the eggs are fewer in number,
and very often _clear_. This is an exact repetition of what took
place in M. Naudin’s datura seeds, which he observed to become
abortive or devoid of embryo.
We must, moreover, exclude from the number of fertile hybrids
a certain number of examples quoted by some authors, and which
statements are proved by facts, now either better known or better
appreciated, to have an erroneous foundation. Thus Hellenius thought
he had crossed the Finnish ram with the Sardinian doe, but he had
confounded the then little known moufflon with the roebuck. He thus
obtained a mongrel, which having been crossed for two generations
with the male parent, returned to the type of the latter. We have
here evidently only a companion experiment to those of Koelreuter,
which resulted in a reversion of the hybrid to the male type under a
similar series of crossings.
There are, however, some examples among birds and among mammalia of
hybrids which have propagated _inter se_ for several generations,
four or five at the most. The celebrated experiment of Buffon upon
the crossing of the dog with the wolf in particular, belongs to this
order of facts. It was unfortunately interrupted by the death of the
great naturalist at the fourth generation. It is clear that there is
nothing here which does not perfectly agree with our observations
upon hybrid plants, which, although exceeding this number of
generations, have never produced hybrid races.
Fertility, and the number of succeeding generations is increased,
when a superiority is given to one of the crossed species over the
other. This fact has been recognised in plants, and we meet with
it again in animals. By crossing and recrossing in a fixed manner
the goat and the sheep, hybrids called _chabins_ are obtained which
possess three-eighths of the paternal and five-eighths of the
maternal blood. These animals produce a fleece much valued in South
America, and are the source of real industry. They can be maintained
for several generations, but at length all the crossings to which
they owe their existence must be recommenced, they having returned to
the parental types, ‘like plants,’ as M. Gay said.
This proportion—three-eighths to five-eighths—appears to be very
favourable to the maintenance of hybrid races; it is the proportion
which characterises the famous leporides, the result of the crossing
of the hare and the rabbit. But can these hybrids, of which so
much has been said, maintain themselves without reverting to the
parental types? M. Roux evidently believed it, and it is still
asserted by M. Gayot. But the testimony of those who have established
and impugned their assertions leaves scarcely any room for doubt.
Isidore Geoffroy, who had at first believed in their fixity, and
had spoken of it as a conquest, did not hesitate afterwards to
admit the reversion. The fact has been established in the Jardin
d’Acclimatation, and M. Roux himself, upon the assertion of M.
Faivre, appears to have abandoned his previous assertions. The
observations and experiments made by the Agricultural Society of
Paris clearly show that the _leporides_, sent or presented by the
breeders themselves, had entirely reverted to the rabbit type.
Lastly, M. Sanson, discussing the anatomical side of the question,
has arrived at the same conclusions. Moreover, whoever will credit
the observations made by M. Naudin upon the Linariæ, will easily
recognise the _reversion_ and the _disordered variation_ exhibited
by the leporides of the Abbé Cagliari, who was the first to obtain a
fertile crossing between the hare and the rabbit.
These phenomena appear in an equally well marked manner in the
result of the cross between the silkmoth (_Bombyx cynthia_) and
the castor-oil silkmoth (_Bombyx arrindia_), obtained by M.
Guérin Méneville. The hybrids of the first generation were almost
exactly intermediate between the two species, and resembled each
other. In the second this uniformity disappeared, in the third the
dissimilarity had increased, some of the insects having reassumed
all the characters of the paternal or maternal types. In the seventh
generation this curious experiment was destroyed by ichneumons. But,
as M. Valée, their intelligent breeder, told me, nearly all the moths
had returned to the type of the Bombyx arrindia. The resemblance to
what took place in the case of M. Naudin’s Linariæ is here complete.
V. The phenomenon of the _reversion_ of the descendants of a hybrid
to the paternal or maternal type, or _disordered variation_, has
given rise to some interpretations which it will be well to rectify,
and has also raised important questions.
The attempt has been made to assimilate the latter to the
_oscillations_ presented by mongrels for some generations. But
daily experience should suffice to refute this opinion. Breeders
are crossing _races_ every day for some purpose or other, and they
would never do so if the crossing were to result in the production
of a disorder which would exhibit the smallest resemblance to that
displayed by the Linariæ of M. Naudin, and the silkmoths of Guérin
Méneville. They expect, however, a few irregularities more or less
marked, in the first generations, but they know that the race will
soon _settle_ while the disorder would only increase if the crossing
had taken place between _species_.
Again, an attempt has been made to consider the facts of _atavism_
and _reversion_ as identical. There is, however, a fundamental
difference between them, for the mongrel which by atavism reassumes
the characters of one of its paternal ancestors, for example, still
preserves its mixed nature. This is proved by the possibility of
its offspring of the first or second generation reproducing, on the
contrary, the essential traits of its own maternal ancestors. Darwin
gives many examples of facts of this nature from the agricultural
history of his country. One of the best to quote is that furnished by
the genealogy of a family of dogs observed by Girou de Buzareingues.
These animals were crosses between the setter and spaniel. Now one
male, a setter to all appearances, united with a female of pure
setter breed, produced spaniels, which makes it evident that the
latter blood was by no means annihilated, and that the return to the
setter type was only apparent.
It is different in the cases of _reversion_ displayed by hybrids,
for one of the two bloods is irrevocably expelled. We are justified
in making this assertion in the case of mammalia, by experience
extending as far back as the Roman period, or at least as far as the
seventeenth century. Titires and musmons have never since those times
had _offspring affected by atavism_. A ram and sheep have never been
known to produce a kid, nor a male and female goat to produce a lamb.
It is the same with plants, according to statements with which M.
Naudin has kindly furnished me.
Far from being similar, the phenomena of _atavism_ and _reversion_
are absolutely different and characteristic, the one of crossing
between _races_, the other of crossing between _species_. The first
proclaims the persistency of the physiological connections between
all the representatives, more or less modified, of one species; the
second proves the complete rupture of the same connections between
the descendants of two species accidentally brought into contact by
the promoter of the hybridism.
VI. In none of the preceding cases has hybridism, no matter in what
degree, given rise to a series of individuals descended the one from
the other; and preserving the same characters. An exception is,
however, known to this general fact. It is unique, and is produced in
the vegetable kingdom from the crossing of wheat with _Ægilops ovata_.
The hybrid of the first generation from these two species is
sometimes produced naturally, and was regarded by Requien as a
species. Fabre, who frequently met with it in the fields, considered
it to be the commencement of the transmutation of the Ægilops into
wheat. Afterwards a quadroon hybrid, accidentally obtained and
cultivated during several years, gave him descendants resembling the
_beardless wheat_ of the South. It was the result of _reversion_.
Fabre, however, who did not recognise the hybrid, thought it was a
transmutation, and flattered himself that he had discovered wild
wheat in the Ægilops.
M. Godron, on the contrary, understood the nature of the phenomenon,
and demonstrated it experimentally. He crossed the Ægilops and
the wheat, and obtained the first plant of Requien, the _Ægilops
triticoïdes_ of Fabre. He again crossed this hybrid with the
true wheat, and reproduced the pretended artificial wheat of
the Montpellier botanist. He gave to it the name of _Ægilops
speltæformis_.
It is this latter form, having as we see three-fourths of the true
wheat, and a fourth of the Ægilops, that M. Godron has cultivated at
Nancy since 1857. The clever naturalist who has produced it, believes
that he has not had one case of reversion like those at Montpellier
and those of Fabre. But at the same time he informs us that the most
minute and special precautions alone can preserve this artificial
plant. The ground must be prepared with the greatest care, and each
seed placed by hand in the desired position. If put into the ground
carelessly, or scattered over the bed, the seeds never germinate.
M. Godron considered that the Ægilops speltæformis would entirely
disappear, perhaps in a single year, if left to itself.
VII. Finally, the characters of hybrids are: infertility, as a
general rule, and, in the exceptions, a very limited fertility;
series suddenly cut short either by infertility, by disordered
variation, or by reversion without atavism.
The Ægilops triticoïdes alone seems to stand in opposition to all
other known facts. This exception is undoubtedly remarkable, but
does not in any way impair our general conclusions. A product of
human industry, this hybrid plant only exists by virtue of the same
industry, and cannot, from any point of view, be compared to the
succession of mongrel individuals which are unceasingly propagated
without our aid, and in spite of our precautions, in the midst of our
animal and vegetable races.
“But,” say those writers who deny the reality of a distinction
between species and race, “what man has done nature must be able
to do also, for she governs space and time, and is therefore more
powerful than man.” This form of argument rests upon a confusion of
ideas and a strange neglect of the most ordinary facts.
Most true, nature is more powerful than man in certain cases and
for certain ends, but man also has his domain, in which he is
much superior to nature. Natural forces act in virtue of blind and
necessary laws, the result of which is constant. Now man has acquired
the knowledge of these laws, he has made use of them to constrain
and master the natural forces one after another, he now knows how
to exaggerate some and to weaken others. In this manner he changes
their resultants, and obtains products which nature herself could not
realise. Give to the latter all the time and space that you will,
she would never be able either to produce or preserve potassium or
sodium in a metallic form; in spite of the physico-chemical forces,
or rather by directing them, man has obtained and preserved these two
metals, as he has obtained and preserved the Ægilops triticoïdes,
which is destroyed by the inflexibility of natural forces as soon as
it is exposed to their action.
VIII. The infertility, or, if you will, the restricted and rapidly
limited fertility between species, and the impossibility of natural
forces, when left to themselves, producing series of intermediary
beings between two given specific types, is one of those general
facts which we call a _law_. This fact has an importance in the
organic world equal to that rightly attributed to attraction in the
sidereal world. It is by virtue of the latter that the celestial
bodies preserve their respective distances, and complete their
orbits in the admirable order revealed by astronomy. The _law of the
sterility of species_ produces the same result, and maintains between
species and between different groups in animals and plants all those
relations, which, in the palæontological ages, as well as in our own,
form the marvellous whole of the _Organic Empire_.
Imagine the suppression of the laws which govern attraction in the
heavens, and what chaos would immediately be the result. Suppress
upon earth the law of crossing, and the confusion would be immense.
It is scarcely possible to say where it would stop. After a few
generations the groups which we call genera, families, orders, and
classes would most certainly have disappeared, and the branches also
would rapidly have become affected. It is clear that only a few
centuries would elapse before the animal and vegetable kingdoms
fell into the most complete disorder. Now order has existed in both
kingdoms since the epoch when organised beings first peopled the
solitudes of our globe, and it could only have been established and
preserved by virtue of the impossibility of a fusion of species with
each other through indifferently and indefinitely fertile crossings.
IX. There are some writers, very often entirely unacquainted
with the natural sciences, who, labouring under the most varied
prejudices, especially that of exaggerating the transmutation
doctrines which I shall presently discuss, have denied the _reality
of species_; they affirm that there are no serious barriers between
the groups designated by this term, and have compared it in a more
or less formal manner to the groups always somewhat arbitrarily
called genera, tribes, families, orders, etc. Though only a brief
recapitulation, the preceding facts would be sufficient to answer
them. It is, however, necessary to mention the principal objections
which are brought forward against such ideas, and to shew how they
may be refuted.
1st. It is useless to take any notice o£ the good humoured or
malicious banter, of the raillery and sarcasm too often made use of
by some writers against those who admit the reality of species. It is
evident that those who employ such weapons do not address themselves
to men of science, but appeal directly to the passions. We cannot
sufficiently express our regret at seeing men of undoubted merit
resorting to such means.
2nd. At the present time, perhaps more than ever, those who believe
in species are reproached with being _orthodox_: I could never myself
understand why there should be this mixture of scientific discussions
and dogmatic and anti-dogmatic polemics.
3rd. I shall, moreover, refuse to dispute with those who, rejecting
on their own authority a whole century of work accomplished by the
greatest naturalists, and by a number of men distinguished in botany
and zoology, declare that it is useless to try and discover what
species and race are, and laugh at those who take the trouble to do
so. I say the same to those who regard species and race as more or
less arbitrary groups which may be compared to the genus, family and
order. It will be enough to remark that they themselves incessantly
employ the word _species_ and _race_, and we must not be surprised if
they take one thing for the other.
4th. After what we have said, discussion is useless with those
naturalists who only base the distinction of species upon external
characters. They forget all the experiments made from Buffon to
the two Geoffroys, from Koelreuter to M. Naudin; they forget the
innumerable observations made in our orchards, gardens and stables.
To refuse to abandon morphological considerations, and to neglect the
data of physiology and the lessons of filiation, is clearly going
further back than Ray and Tournefort, and all discussion becomes
impossible.
5th. Some of our opponents allow that things are now what we think
them to be. “But,” say they, “it is possible that at some other
time it was different.” What answer can be given to those who base
their arguments upon _possibilities_? Is modern science composed of
possibilities?
6th. Naturalists have often been reproached with multiplying the
definitions of species. From the variety of terms employed by them in
expressing ideas, it has been inferred that they were not agreed as
to the ideas themselves. We may easily convince ourselves of their
mistake, if we give these definitions a careful reconsideration. We
shall see that their several authors have only endeavoured to express
with greater clearness and precision, the double idea resulting from
the facts of resemblance and filiation. In reality, divergencies only
begin where experiment and observation cease. It is this which caused
Isidore Geoffroy, however interested he might be in discussions of
this nature, to remark—“Such are Species and Races, not only for one
of the schools into which naturalists are divided, but for all.”
7th. It has been asserted that the distinction of species and race
rests upon a syllogistic circle; that naturalists decided _à priori_
upon calling all those groups incapable of intercrossing, _species_,
and all those amongst which crossing was possible, _races_. To appeal
to the difference of the phenomena presented by the hybrids and
mongrels is therefore only solving the question by the question.—This
is an historical error. Naturalists came into contact with species,
races and varieties, before they gave names to them. It was by
experiment and observation that they learnt to distinguish them.
_Knowledge of facts_ preceded _terminology_.
8th. Again, it has been said, that the discussions which are always
arising between naturalists as to whether a species should be
preserved or regarded as a race, as to the genus, family, order, and
sometimes the class in which it should be placed, betray a want of
precision in general ideas.—Those who talk in this manner forget the
immense number of species and races accepted and classified without
discussion. They shut their eyes to all cases except those in which
divergences of opinion occur. If, however, facts of this nature
prove anything against a science and its fundamental data, then even
mathematical theorems must be considered as wanting in precision, for
there are disputes among mathematicians.
9th. I have already replied to the arguments drawn from the fertility
of certain hybrids by showing to what it is reduced. Writers who
insist upon this point invariably forget the lesson taught us by
disordered variation and reversion without atavism. I regret being
obliged to place among them Darwin, who, in his later writings, has
shewn much less reserve than in his earlier publications. In the last
edition of his book, he quotes what I have said of the cross between
the Bombyx cynthia and the Bombyx arrindia; he speaks of the number
of generations obtained, but he forgets to mention that disordered
variation appeared in the second generation, and that reversion to
one of the parental types was almost complete at the termination of
the experiment.
X. Species is then a reality.
Let us take a group of individuals more or less similar, but always
capable of contracting fertile unions, and let us, with M. Chevreul,
trace it in imagination to its origin. We shall see it divided
into _families_, each of which will have risen either mediately or
immediately from one pair of parents. We shall see that the number of
these families decrease at _each generation_, and rising still higher
we shall at length find the initial term of a _single primitive pair_.
Has this really been the case? Has each species indeed arisen from
one single pair, or have several pairs, resembling each other
perfectly both morphologically and physiologically, appeared
simultaneously or successively? These are _questions of fact_ which
science neither can nor ought to approach, for neither experiment nor
observation is able to furnish us with the smallest data requisite
for the solution.
But what science may affirm is that _from all appearances_ each
species has had, as point of departure, a single primitive pair.