THE LAW OF SIMILARITY
A powerful instinct keeps animals from pairing with individuals
belonging to another species than their own. “L’animal,” says
M. Duvernoy, “a l’instinct de se rapprocher de son espèce et de
s’éloigner des autres, comme il a celui de choisir ses aliments et
d’éviter les poisons.”[1629] Among Birds, there are found a small
number of wild hybrids, nearly all of which are in the order of
Gallinae, and most of which belong to the genus Tetrao.[1630] But among
Insects, Fishes, and Mammals, living in a state of nature, hybridism
is unknown or almost so.[1631] And, even among domesticated mammals,
some tricks are often required to deceive the male, and so to conquer
its aversion to a female of a different species. The stallion, for
instance, who is to cover a she-ass, is frequently first excited by the
presence of a mare, for which, at the proper moment, the she-ass is
substituted.[1632]
We may be sure that, were it not for this instinctive feeling, many
more animal hybrids would be naturally produced than is the case. In
the vegetable kingdom, where the play of instincts is altogether out
of the question, bastards occur much more frequently;[1633] and in
captivity a considerable number of animal hybrid forms are produced
that are never met with in a state of nature.[1634] Yet, according to
Mr. Darwin, there are good grounds for the doctrine of Pallas, that
the conditions to which domesticated animals and cultivated plants
have been subjected, generally eliminate the tendency towards mutual
sterility, so that the domesticated descendants of species which
in their natural state would have been in some degree sterile when
crossed, become perfectly fertile.[1635]
The origin of this instinct, which helps to keep even closely allied
species in a state of nature distinct, seems to be sufficiently clear.
The number of species which have proved fertile together are very
limited, and the fertility of the hybrid offspring is almost constantly
diminished, often even to a very great extent. Of course, no one
now talks of the sterility of hybrids as a moral necessity—hybrids
being _animalia adulterina_,—or as the result of a special divine
decree, that new species should not be multiplied indefinitely.[1636]
M. Isidore Geoffroy has shown not only that hybrids may be fertile,
but that “infertile” hybrids are, properly speaking, merely the
hybrids which are most rarely fertile, their sterility never being
absolute.[1637] Moreover, as has been pointed out by Mr. Wallace, in
almost all the experiments that have hitherto been made in crossing
distinct species, no care has been taken to avoid close interbreeding;
hence these experiments cannot be held to prove that hybrids are
in all cases infertile _inter se_.[1638] But looking to all the
ascertained facts on the intercrossing of plants and animals, we may
with Mr. Darwin conclude that some degree of sterility in hybrids is an
extremely general result.[1639] This being the case with the hybrids of
our domesticated animals, it must be so all the more with animals in a
state of nature, which generally live under conditions less favourable
to mutual fertility. It is easy to understand, then, that instincts
leading to intercrossing of different species, even if appearing
occasionally, never could be long-lived, as only those animals which
preferred pairing with individuals of their own species, gave birth
to an offspring endowed with a normal power of reproduction, and thus
became the founders of numerous generations that inherited their
instincts.
The relative or absolute sterility characterizing first crosses and
hybrids depends upon a biological law which might be called the “Law
of Similarity.” The degree of sterility, in either case,[1640] runs,
at least to a certain extent, parallel with the general affinity of
the forms that are united. Thus, most animal hybrids are produced by
individuals belonging to the same genus, whilst species belonging to
distinct genera can rarely, and those belonging to distinct families
perhaps never, be crossed.[1641] The parallelism, however, is not
complete, for a multitude of closely allied species will not unite,
or unite only with great difficulty, though other species, widely
different from each other, can be crossed with facility. Hence Mr.
Darwin infers that the difficulty or facility in crossing “apparently
depends exclusively on the sexual constitution of the species which
are crossed, or on their sexual elective affinity, _i.e._, the
‘Wahlverwandtschaft’ of Gärtner.” But as species rarely, or never,
become modified in one character, without being at the same time
modified in many, and as systematic affinity includes all visible
resemblances and dissimilarities, any difference in sexual constitution
between two species would naturally stand in more or less close
relation with their systematic position.[1642]
With regard to the instinct in question, man follows the general rule
in the animal kingdom. Our notions of morality are closely connected
with the instinctive feelings engraved in our nature; and bestiality
is commonly looked upon as one of the most heinous crimes of which man
can make himself guilty. Several passages both in ancient[1643] and
modern writers[1644] prove the occasional occurrence of this crime, but
always under circumstances analogous to those under which single birds
sometimes form connections against nature,[1645] _i.e._, either because
of isolation, or on account of vitiated instincts.[1646]
* * * * *
Supporters of the hypothesis that the several races of man are distinct
species of the genus Homo, assert that an instinctive aversion similar
to that which keeps different animal species from intermingling, exists
also between the various human races.[1647] It may be noted by the
way that, even if this were true, the idea that mankind consists of
various species might be controverted; for certain races of domestic
or semi-domesticated animals seem to prefer breeding with their own
kind and refuse to mingle with others. Thus Mr. Bennett states that
the dark and pale coloured herds of fallow deer, which have long been
kept together in the Forest of Dean and two other places, have never
been known to mingle. On one of the Faroe Islands, the half-wild native
black sheep are said not to have readily mixed with the imported white
sheep. And in Circassia, where six sub-races of the horse are known and
have received distinct names, horses of three of these races, whilst
living a free life, almost always refuse to mingle and cross, and will
even attack each other.[1648] As for man, there are many races who
dislike marrying persons of another race, but the motives are various.
The different ideas of beauty no doubt play an important part. Mr.
Winwoode Reade does not think it probable that negroes would prefer
even the most beautiful European woman, on the mere grounds of physical
admiration, to a good-looking negress.[1649] A civilized race does not
readily intermingle with one less advanced in civilization, from the
same motives as those which prevent a lord from marrying a peasant
girl. And more than anything else, I think, the enmity, or at least,
want of sympathy, due to difference of interests, ideas, and habits,
which so often exist between distinct peoples or tribes, helps to keep
races separate. But such reasons as these have nothing in common with
the instinctive feeling which deters animals of distinct species from
pairing with each other. Hence, when two races come into very close
mutual contact, especially if they are at about the same stage of
civilization, their dislike to intermarriage commonly disappears.
Mongrels form, indeed, a large proportion of the inhabitants of the
world. It is doubtful whether there are any pure races in Europe; not
even the Basques can pretend to purity of blood.[1650] M. Broca found,
when investigating the subject of stature, that nineteen-twentieths
of the whole population of France presented, in various degrees, the
characters of mixed races.[1651] In North America, different races
intermingle more and more every day. In Greenland, according to Dr.
Nansen, in the course of a century and a half there has been such
an intermixture of races that it would now be extremely difficult,
if not impossible, to find a true Eskimo throughout the whole of
the west coast; and the Europeans, far from being disliked by the
native women have succeeded in inspiring them with so much respect
that the “simplest European sailor is preferred to the best Eskimo
seal catcher.”[1652] In Mexico, the Spanish mixed breeds constitute
two-thirds or three-fourths of the whole population;[1653] and South
America, to quote a French writer, is “le grand laboratoire des
nations hybrides ou métisses modernes.”[1654] Of twelve millions of
mongrels, which is the estimated number of mongrels on the face of
the globe, no fewer than eleven millions are found there.[1655] Even
in remote Tierra del Fuego, according to Mr. Bridges, some mongrels of
European fathers and indigenous mothers have appeared during the last
few years.
In Asia there are numberless instances of intermixture of breed between
the Tartars, Mongols, and Tunguses, and the Russians and Chinese,
&c.[1656] In India there are many Eurasians; in the Indian Archipelago
Chinese and Malays intermarry;[1657] and, in the Islands of the South
Sea, the mongrels of European fathers amount to a considerable number.
In Africa, the eastern Soudan is a great centre of mixed breeds between
races much removed from one another. And, in Southern Africa, the
Griquas—the offspring of Dutch colonists and Hottentot women—form a
very distinct race.
As far as we know, there are no human races who, when intermingled,
are entirely sterile. But as regards the degree of fertility of first
crosses and of mongrels, the opinions of different anthropologists
vary considerably. Those who do not believe in the unity of the human
race have been especially solicitous to prove that crosses are almost
inevitably followed by bad results in that respect. Thus Dr. Knox
thinks that the half-breeds, if they were abandoned to themselves
and no longer had access to pure races, would rapidly disappear, the
“hybrid” being rejected by nature as a degradation of humanity.[1658]
Dr. Nott asserts that, when two proximate species of mankind, two
races bearing a general resemblance to each other in type, are bred
together, they produce offspring perfectly prolific; but that, when
species the most widely separated, such as the Anglo-Saxon and the
negro, are crossed, the mulatto offspring are but partially prolific,
and acquire an inherent tendency to run out, and become eventually
extinct, when kept apart from the parent stocks.[1659] The same opinion
is entertained by M. Broca, and by M. Pouchet, who thinks that the
crossed race will exist only if it continues to be supported by the
two creating types remaining in the midst of it.[1660]
On the other hand, Dr. Prichard believes it may be asserted, without
the least chance of valid contradiction, that mankind, of all races and
varieties, are equally capable of having offspring by intermarriage,
and that such connections are equally prolific whether contracted
between individuals of the same variety or of the most dissimilar
varieties. “If there is any difference,” he says, “it is probably
in favour of the latter.”[1661] According to M. Godron, the mongrels
have generally shown a higher degree of fertility than their parent
races;[1662] and M. Quatrefages asserts that mulattoes are as fruitful
as pure breeds.[1663]
It is to be regretted that so little attention has for some time been
paid to this most important question. The result is that the effects
of the intermixture of races are not much better known now, than they
were twenty or thirty years ago. The only thing which may be considered
certain is, that the hypothesis of the depressing influence of crossing
upon fertility, as the theory has generally been propounded, involves
a great deal of exaggeration. It is chiefly owing to M. Broca’s
celebrated essay, ‘Sur l’hybridité,’ that this doctrine has been so
widely accepted. He asserts that the connections of Europeans with
Australian women have proved very slightly prolific, and that the
mongrels resulting from them are almost sterile. “No statistical
writer,” he says, “nor any historian, enumerates cross-breeds among
the Australian population.”[1664] Yet, this land has for a considerable
time been inhabited by European colonists, many of whom have not had
opportunities of marrying wives of their own race. It has also been
shown that the cohabitation of whites and native women is very common
in Australia. But the number of mongrels there is, nevertheless,
exceedingly small, so small that in the native dialects there does not
exist a single word to designate them.[1665]
Supposing that these remarkable statements referred chiefly to the
eastern and southern parts of the Australian continent, I asked Bishop
R. Salvado and the Rev. Joseph Johnston, living in West Australia, to
inform me whether, in that country, any mixed race exists, and, if so,
whether it is fruitful or not. From the former, who has lived among the
West Australian aborigines for more than forty years, and through an
excellent work on their life and customs has gained the reputation of
a first-rate authority, I had the pleasure of receiving the following
answer, dated New Norcia, October 17, 1888:—“With regard to the
sterility of the half-caste natives, of which I had no experience when
I wrote my book, I am able now to deny it altogether, except in cases
similar to those among the Europeans. I know several cases of husband
and wife, half-caste natives, having at present six and seven and even
eight children, and they may in time have more; and I know a good many
Europeans who, having married native women, have several children. In
fact, in the case of one of those marriages there were six children,
and in another seven, and I could give the name of each of them.”
The Rev. J. Johnston writes, “There is a school for half-caste boys
and girls at Perth, and they seem bright and intelligent children,
not unlike Polynesian children. As they grow up, they go out to
service, and some of the youths are employed as post and telegraph
messengers.... At the New Norcia mission, there are several half-caste
families, as well as blacks, and they all have children.” The following
statement of Mr. Taplin referring to the aborigines of the Lower
Murray, goes in the same direction:—“The pure blacks,” he says,
“are not so healthy as the half-castes. Always the children of two
half-castes will be healthier and stronger than either the children of
blacks or the children of a black and a half-caste. When a half-caste
man and woman marry, they generally have a large and vigorous family. I
could point to half a dozen such.”[1666]
These statements of highly competent persons are, I think, quite
sufficient to disprove M. Broca’s hypothesis. They show that, if
a mixed race is almost wanting in certain parts of Australia, this
does not depend upon physiological conditions of the kind suggested.
It should be remembered that the sexual intercourse of Europeans
with savage women is most commonly transitory and accidental, and
frequently takes place with prostitutes or licentious women, who are
generally known to be sterile. And, even when the white settler takes
a native’s daughter to live with him under his own roof as a wife or
a concubine, and accustoms her to a half-civilized manner of living,
her unfruitfulness[1667] may be owing to quite another cause than the
mixture of blood. Mr. Darwin has shown that changed conditions of
life have an especial power of acting injuriously on the reproductive
system. Thus animals, as also plants, when removed from their natural
conditions, are often rendered in some degree infertile or completely
barren, even when the conditions have not been greatly changed. And
this failure of animals to breed under confinement cannot, at least
to any considerable extent, depend upon a failure in their sexual
instincts. “Numerous cases,” says Mr. Darwin, “have been given of
various animals which couple freely under confinement, but never
conceive; or, if they conceive and produce young, these are fewer in
number than is natural to the species.”[1668] It is reasonable to
suppose that savage man, when he moves into more civilized conditions,
is subject to the same law. Indeed, statements have been reported to
me, which tend to show that the indigenous women at the Polynesian
missionary stations have become less fruitful than they were in their
native state. As to the alleged sterility of crosses between the
European and Australian races, it should be observed that the rarity
of mongrels in certain parts of Australia is more or less owing to
the natives themselves habitually destroying the half-castes.[1669]
The Rev. A. Meyer states that, in the Encounter Bay tribe, “nearly
all the children of European fathers used to be put to death;”[1670]
whilst, among the Narrinyeri, about one-half of the half-caste infants
fell victims to the jealousy of their mothers’ husbands.[1671] But
with regard to the West Australian aborigines in the neighbourhood of
Fremantle, the Rev. J. Johnston writes that he does not think it has
been the custom there to destroy the half-caste illegitimate offspring
of black women, as he never heard of such a thing,—a fact which may
account for the comparatively large number of mongrels in that part of
the continent.
Other statements also, adduced as evidence for the hypothesis of
M. Broca, have proved more or less untrustworthy. Thus the alleged
sterility of the mulattoes of Jamaica[1672] has been disputed by other
writers.[1673] So also v. Görtz’s statement that the children of the
Dutch and Malay women in Java (Lipplapps) are only productive to the
third generation,[1674] has been called in question.[1675]
Yet, although we may consider it certain that the diversities even
between the races which least resemble each other are not so great
but that, under favourable conditions, a mixed race may easily be
produced, I do not deny the possibility of crossing being, to a certain
extent, unfavourable to fertility. The statements as to the rapid
increase of some mixed races do not prove the reverse. For the bad
result of crossing would not necessarily appear at once; and a drop
of pure blood would be sufficient to increase fertility, just as,
when a hybrid is crossed with either pure parent species, sterility
is usually much lessened.[1676] It is a remarkable fact that mixed
marriages between Jews and persons of other races are comparatively
infertile. In Prussia, these marriages have been separately registered
since 1875, and between that year and 1881 there was an average of
1·63 to a marriage, whereas, during the same period, pure Jewish
marriages resulted in an average of 4·41 children or very nearly three
times as many. In Bavaria, between 1876 and 1880, the numbers were
only 1·1 per marriage against 4·7 children to purely Jewish marriages.
And this conspicuous infertility implies greater sterility. Among
fifty-six such marriages, with regard to which Mr. Jacobs ascertained
the results, no fewer than nine were sterile, _i.e._, 18 per cent.,—a
striking contrast to the number of sterile marriages which he found in
seventy-one marriages between Jewish cousins, where the percentage of
sterility was only 5·4 per cent.[1677] Mr. Jacobs, however, informs
me that it has been suggested that this infertility may be due rather
to the higher age at which such marriages are likely to take place.
There is still a strong feeling against them among Jews, which is
only likely to be overcome after independence of thought and position
has been reached. At the same time Mr. Jacobs does not consider this
sufficient to account for the very great discrepancy. But we must not,
of course, take for granted that the crossing of any two races has the
same effects as the crossing of Jewish and non-Jewish Europeans seems
to have.
Even if it could be proved, however, that mixture of races produces
lessened fertility of first crosses and of mongrels, this would not
make it necessary for us to reject the doctrine of the unity of
mankind. It is true that the domesticated varieties both of animals and
of plants, when crossed, are as a general rule prolific, in some cases
even more so than the purely bred parent varieties; whereas species,
when crossed, and their hybrid offspring, are almost invariably in some
degree sterile. But this rule is not altogether without exceptions.
Even Agassiz condemned the employment of fertility of union as a
limiting principle. He considered this a fallacy, “or at least a
_petitio principii_, not admissible in a philosophical discussion of
what truly constitutes the characteristics of species.”[1678] Thus the
red and yellow varieties of maize are in some degree infertile when
crossed, and the blue-and the red-flowered forms of the pimpernel,
considered by most botanists to be the same species, as they present no
differences of form or structure, are, according to Gärtner, mutually
sterile. Moreover, Mr. Darwin’s investigations on dimorphic and
trimorphic plants have shown that the physiological test of lessened
fertility, both in first crosses and in hybrids, is no safe criterion
of specific distinction.[1679] As for animals, Professor Vogt asserts
that, in the opinion of experienced breeders, certain races can with
difficulty be made to pair, and the fertility of the mongrels soon
diminishes, whilst other races pair readily and are prolific.[1680]
Sir J. Sebright says, “Although I believe the occasional intermixture
of different families to be necessary, I do not, by any means, approve
of mixing two distinct breeds, with the view of uniting the valuable
properties of both: this experiment has been frequently tried by others
as well as by myself, but has, I believe, never succeeded. The first
cross frequently produces a tolerable animal, but it is a breed that
cannot be continued.”[1681]