all great work in art, literature, or science take place
unconsciously, or at least unwittingly. It is an interesting
question to ask whence comes the energy of which this work is the
expression. There are two chief possibilities: one, that it is
derived from the instinctive tendencies which, through the action
of controlling forces, fail to find their natural outlet; the
other, that the energy so arising is increased in amount through
the conflict between controlled and controlling forces.”--W. H.
RIVERS.
The biology of sex is a vast subject. Not only are there questions of
sex-determination, but the whole sexual selection problem has to be
considered, together with the evolutionary function of sex, and its
first origin. I can only attempt, in the short space at my disposal, to
deal with one or two of the chief points, and only in so far as they
bear on questions of human sex psychology.
In the first place, then, we have to consider the evolutionary history
of sex. Of its origin we can say only that it is veiled in complete
obscurity. Once present, however, it appears to have a definite
function by making possible, through sexual reproduction, all the
various combinations of any heritable variations that may arise
in different individuals of a species, and so conferring greater
evolutionary plasticity on the species as a whole.[28]
Primarily, sex implies only the fusion of nuclei from two separate
individuals; there is no need for sex differences to exist at all. Sex
differences, however, are almost universal in sexually-reproducing
organisms, and represent a division of labour between the active male
cell and the passive female cell, the former taking over the task of
uniting the two, the latter storing up nutriment for the new individual
that will result from that union.
The subsequent history of sex is, roughly speaking, the history of its
invasion of more and more of the organization of its possessors. First
the male as a whole, and not merely its reproductive cells, tends to
become organized for finding the female. The female’s whole type of
metabolism is altered to produce the most efficient storage of reserve
material in her ova, and later she almost invariably protects and
nourishes the young during the first part of their development, either
within or without her own body. Appropriate instincts are of course
developed in both male and female.
At the outset there is enormous waste incurred in the liberation of
sperms and ova into the water, there to unite as best they may.
Congress of the sexes eliminates the major part of this waste, and is
universal above a certain level. This is in itself the basis for other
changes. As the mind, or shall we say the psycho-neural organization,
becomes more complex, the sexual instinct becomes more interwoven with
the general emotional state; and a large number of animals appear not
to mate unless their emotional state has been raised to a certain
level. The result of this is that special actions, associated generally
with bright colours or striking structures, with song or with scent,
come into being.
The exact mechanism of the appearance of these courtship-displays is a
much-vexed point; but it is undoubted that they only occur in animals
with congress of the sexes and with minds above a certain level of
complexity, and that they are employed in ceremonies between the two
sexes at mating-time. There can subsist no reasonable doubt that there
exists some causal connection between the associated facts.
An important point, which has been commonly overlooked, is that such
characters and actions may be either developed in one sex only, or in
both. In a large number of birds, such as egrets, grebes, cranes, and
many others, the courtship-displays are mutual, and the characters used
in them developed to a similar extent in both sexes. Such characters
are therefore often not secondary sexual differences, and we had best
use Poulton’s term _epigamic_ for them, whether they are developed in
one or in both sexes.[29]
The human species, in accordance with its complexity and flexibility
of brain, has epigamic characters of both kinds. Some, like voice and
moustache, are different in the two sexes, others, such as colour of
eyes and lips, the hairlessness of the body and grace of limbs and
carriage, are common to both.
In the vertebrate stock, two main lines of evolution as regards
sexual relationships may be traced. The first is predominant in
mammals: here, in most species, the female will not receive the male
except at fixed times, which are determined by a purely physiological
mechanism, the internal secretion of the gonad (reproductive organ).
Here we consequently find that the rule is for the males to fight for
the possession of the females, not to display before them. In the
monkeys, presumably as a result of a lessened dependence of mental
upon physiological processes, bright colours and special adornments of
various parts of the body are frequently developed.[30]
In the birds, on the other hand, although here too the internal
secretion of the gonad delimits a period in which alone congress of
the sexes can occur, it does not act for such a sharply-limited time
as in the mammal, nor is it so intense as completely to override
other components of the mind. As a result, general emotional stimulus
may play an important part in inducing readiness to pair, and we
accordingly find display of some sort, either by the male alone or by
both sexes, present in the great majority of species. It is at least
partly in correlation with this that beauty of voice and brilliant
appearance is far commoner in birds than in mammals.
The monkeys represent in some way a transitional stage towards that
seen in man, in whom the conditions have come to resemble those found
in birds, with consequent great development of epigamic characters and
actions of one sort and another, both physical and mental. Thus we see
that sex, after invading and altering the conformation of the body,
finally invades and alters the conformation of the mind.
As regards the other great biological question, of the determination of
sex, a very few words will suffice. In the first place I have no time
to consider plants or lower animals. In almost all higher animals that
have been investigated, however, there has been found some hereditary
mechanism for ensuring a rough constancy of sex-ratio. This mechanism
resides in the so-called _chromosomes_ of the nucleus. These exist
for the most part in similar pairs in both sexes: but one pair is
dissimilar in one sex. In mammals and man this sex is the male. Man
possesses one chromosome less than woman. He possesses only one member
of this pair of special sex-chromosomes, whereas she possesses two. All
her ova are alike in possessing one, whereas half his sperms possess
one, half possess none. Therefore, when the former kind of sperms
fertilize an ovum, two sex-chromosomes are present in the fertilized
egg and a female results; when the latter, only one, and the offspring
is male.[31]
Putting the matter in the broadest terms, we can say that there is a
different balance of hereditary factors in male and female, and that
this difference of balance dates from the moment of fertilization, and
normally determines sex.
Various agencies may alter the balance. The chromosomes themselves may
vary in what we must vaguely call their potency; or external agencies
may affect it. As a result, we sometimes obtain strange abnormal
individuals, in which the balance has been upset; in them development
results sometimes in organisms permanently intermediate between male
and female, sometimes in a change of sex at some period of development.
In insects the chromosomes appear to be predominant throughout life.
In vertebrates, however, they seem to play their chief rôle in early
development, ending by building up either a male or a female gonad in
the early embryo. This, once produced, takes over what remains of the
task of sex-determination. It secretes a specific internal secretion
which in a male acts so as to encourage the growth of male organs and
instincts, to suppress those of females; and vice versa in a female.
As a result of this difference we find that castration in insects, even
followed by engrafting of a gonad of opposite sex, produces no effect
upon other sexual characters; whereas it exerts a profound effect upon
mammals or birds.
As a second result, we find that in vertebrates the gonads form part
of what has been called the chemical directorate of the body--the
interlocking system of endocrine glands, each of which is exerting an
effect upon the rest. The importance of this is seen in the experiments
of Steinach, Sand, Voronoff, and others, who have been able to obtain
a rejuvenating effect in senile mammals by increasing, by various
methods, the amount of secreting reproductive organ in the body.[32]
To what then has our rapid survey led us? The actual origin of sex
is lost to us in the mists of a time inconceivably remote. Its
preservation once in existence, and its present all-but-universal
distribution seem to be definitely associated with the biological
advantage of the plasticity which it confers. Later, the primary
difference between male and female--their power of producing different
sorts of reproductive cells--leads on to secondary differences.
These differences may be biologically speaking non-significant, mere
accidents of the primary difference. Or they may be in the nature
of a division of labour between the sexes, this division of labour
usually concerning the protection of the embryo or the care of the
young, or more rarely the preservation of the individual itself. Or,
finally, they may concern the more efficient union of the gametes;
such differences may merely affect the ducts and apertures of the
reproductive system, and be more or less mechanical; or they may
concern the use of these systems, in the form of still mechanical
instincts, or they may be concerned in some way or other with the
emotional side of the animals, and consist in characters and actions
which stimulate the emotions of the other sex, characters which we have
termed epigamic.
It is only in higher groups that these emotion-stimulating sexual
characters arise, for only in them has mind reached a sufficient degree
of perfection. But even though detailed study reveals in a bird or a
mammal a mental life of a complexity far more considerable than the
average man would imagine, yet on the whole it is straightforward and
its currents run fairly direct from stimulus to fulfilment.
When we reach man, however, the whole aspect of the matter changes.
The change is most marked, naturally, in his mental organization.
Through his powers of rapid and unlimited association, any one part of
his experience can be combined with any other; through his powers of
generalizing and of giving names to things, his experience is far more
highly organized than that of any animal; through speech and writing he
is inheritor of a continuous tradition which enormously enlarges his
range of experience. Again, he can frame a purpose and thus put the
objective of his actions far further into the future than can lower
organisms.
There are, however, also changes of considerable biological importance
on the physical side. Man brings with him from his animal ancestors
the endocrine secretory mechanism of the reproductive organs: but his
life is not subordinated to it in such an iron-bound way. To start with
he has gradually lost all semblance of a breeding-season. Traces of
it survive in some primitive races, but in civilized communities all
one can say is that the number of births may show a slight seasonal
variation; and the reproductive organs are capable of function in all
twelve months of the year--a state of affairs known, I believe, in no
other vertebrate, or at least in no wild species.[33]
In the second place, there has been in the female a further
emancipation of the sexual life. In all other mammals the female will
only receive the male at certain well-defined periods, which in their
turn depend on cyclical changes in the ovaries. In man this restriction
has been overcome, and, in spite of the survival of a certain degree
of cyclical change in feeling, neither sex is restricted any longer
to certain physically-determined periods for the consummation of its
sexual life. This is, we may say, a triumph of mind over matter in the
human organism, of the mental elements of the sexual life over the
purely physical elements.
This is not to deny that the sexual life of man is dependent upon
the reproductive hormones. It is apparently necessary for proper
activation of the sexual centres in the brain that there should occur
a continuous liberation of secretion from the reproductive organs
into the blood. Again, the mental activities of man are so much more
important than those of other forms that even the cessation of activity
of the reproductive organs, for instance in the female at the change of
life, or even their total removal, need not prevent the continuation,
albeit in a modified form, of the sexual life in its varied indirect
manifestations.
Before attempting to probe the intricacies of the mental side of the
subject, we had better see what we can learn of the physical. Let
us first remind ourselves of one or two facts gained from animal
experimentation. In the first place, in mammals the activation of the
sexual instincts of one or the other sex appears to be completely
or almost completely under the control of the internal secretions
of the reproductive organs. Steinach and others have taken new-born
male guinea-pigs and have removed their testes and grafted ovaries
in their place. The result has been an animal almost completely
feminized both as regards body and mind. In some of the animals milk
was secreted, and when this occurred they would act as foster-mothers
to new-born guinea-pigs of other parents. The reverse operation, the
masculinization of females, was equally successful, the animals growing
large and showing all the instincts of a normal male and none of those
of a normal female.
A similar dependence of behaviour on gonad is seen in fowls. Here
nature makes a number of experiments, which have recently been studied
by Dr. Crew of Edinburgh. When the ovaries of a hen are affected by a
certain type of tumour, the bird stops laying, her comb and wattles
enlarge to the size of a cock’s, her spurs grow, she begins to crow,
her plumage changes at the moult and becomes cock-like, and finally
she becomes indistinguishable from a male. Indistinguishable, even in
behaviour: her years of feminine routine in laying and brooding are
forgotten: the secretion of the altered ovary now apparently resembles
that of a testis and stimulates centres of the brain which would
otherwise have remained permanently dormant. She struts and crows,
fights and mates, and the memory of the previous part of her life is
for all practical purposes lost, since the centres for female activity
are no longer stimulated at all.
Various workers have even experimentally produced a state of
hermaphroditism in mammals by simultaneous grafting of portions of
testes and ovary: the behaviour here oscillates between male and
female.[34]
It is quite clear from these and other facts that in higher vertebrates
there are present in every individual of either sex the nervous
connections which give the possibility of either male or female
behaviour; but that normally only one of these two possibilities is
realized, since for the potentiality of action given by the nervous
connections to become actual as behaviour it is necessary for the
nervous system to be activated by the secretion of one or other of
the reproductive organs. Castrated animals fail to realize either
possibility of normal sex-behaviour, although their nervous machinery
is untouched.
There are, further, some facts of observation which, even if they have
not yet been fully analysed by experiment, still throw light on the
matter. Although many of the most familiar birds--fowls, pheasant,
peacock, duck, finches, and so forth--have bright-coloured males and
drab females, with marked difference of behaviour between the sexes,
there are, as we have seen, many others, such as herons, divers, swans,
grebes, moorhens, and auks, in which the sexes are alike in plumage
and furthermore show what may be called a “mutual” courtship in which
both male and female play similar rôles. In this latter class it seems
clear that the secretions of the male and female reproductive organs
must be more alike than in the markedly dimorphic species: and this
is borne out by some strange facts regarding not merely the courtship
but the actions concerned with pairing itself. In the crested grebe
and the little grebe, for example, close observation has shown that
either member of the pair may assume the passive “female” attitude or
the active “male” attitude in pairing: and in the moorhen we meet with
the still more extraordinary phenomenon of double pairing, in which an
act of pairing with male and female in normal position is immediately
followed by a second act in which the normal position is reversed.[35]
It would appear in such cases that the similarity of male and female
internal secretion is so great that quite slight changes in nervous or
metabolic activity can cause the nervous centres for the opposite sex’s
mode of behaviour to become activated.
In human beings we are confronted with various grades of sexual
organization and behaviour besides the typically feminine and the
typically masculine. In the first place it is matter of common
knowledge that many women, who so far as their physical reproductive
capacity goes are perfectly normal, show various mental traits which
are more characteristic of men, and vice versa. What is more, the
“masculinoid” woman (to use the current jargon) tends physically
also to be less feminine, to have the feminine secondary sexual
characteristics in stature, form of skeleton, distribution of fat,
breasts, etc.--less strongly developed than normal, while the
“feminoid” man shows the reverse tendency.[36]
In trying to analyse these facts further, we are brought up against new
depths of complication. It is becoming ever clearer that the gonads do
not operate as independent organs, but in conjunction with the whole
of the rest of the endocrine system--thyroid, pituitary, adrenal, and
the rest. In the first place, it seems to be established that the
reproductive organs must be in some way activated by other ductless
glands before they become normal, just as they in their turn must
activate the sexual centres in the brain. This phase of the matter is
being investigated by many workers to-day; provisionally we may say
that pituitary and adrenal cortex are especially concerned. In the
second place the gonads, once activated and in normal working order,
react upon the other ductless glands. It thus comes about that the
relative proportion or relative activity of the parts of the whole
ductless gland system is different in male and female. Blair Bell is
the protagonist of this view. A woman is a woman, he says, not merely
because of her ovaries, but because of all her internal secretions, of
her endocrine balance as a whole.
It cannot be said that we have any certainty on the details of this
subject. It is clear, however, that some such fundamental difference
does exist, and it is therefore further probable that if a woman has a
thyroid, say, or an adrenal which for some reason (and there are many
possible reasons) is producing an amount of secretion abnormal for a
woman but more like that which is produced by a man, she will, in spite
of her ovaries, be more masculine in tendency.
I will content myself with one example. The cortex of the adrenal
gland, if active beyond a certain measure, assists the development
of male, prevents the development of female, characters. Women with
adrenal tumours frequently develop moustache and beard and other
appanages of the male. One presumes that a slight preponderance of the
adrenal cortex in the normal endocrine make-up will lead to a less
feminine type of woman than normal. I repeat that we are but on the
verge of the matter and that premature speculation is certainly risky
and probably fallacious. But all the same, there is very little doubt
that we are on the right track, and that we shall have to search for
the finer shades of temperamental difference between man and woman
not so much in differences in the quality of the secretion of testis
or ovary as in differences of balance in what the Americans call the
“endocrine make-up.”[37]
There is, however, also the possibility of difference in the quality
of gonad secretion, and of recent years Steinach and his followers
have been claiming that this may be at the bottom of many cases of
so-called “perversion of sexual instinct.” The latest claim of this
school is that homosexual men may be rendered heterosexual in instinct
by removal of their testes and implantation of a testis from a sexually
normal person--from a man, for example, who is being operated on for
cryptorchidism. It is frankly impossible as yet to say whether their
conclusions are well founded: a very much larger series of cases
will be necessary, and the possibility of suggestion’s action must
be eliminated. It is well to remember, however, that there is no
theoretical objection to the possibility. We know that in various
lower animals, such as moths and flies, the balance between the
male- and female-determining factors in the chromosomes may be altered
in certain crosses, and that this altered balance in the constitution
is reflected in some cases in a state permanently intermediate
between male and female, in others by a reversal of sex at some point
during development. For various reasons we should not usually expect
reversal in mammals; but if such abnormal balance should exist in the
constitution, as it well might, we should expect a gonad secreting an
abnormal, intermediate secretion. This we might also expect as the
result of certain accidents of embryonic life, as actually happens in
the abnormal female cattle known to farmers as free-martins. These
animals are always born co-twin to a male, and their abnormality is due
to the blood-systems of the embryonic membranes of the twins having
fused, so that the secretion of the developing male’s gonad acts upon
the developing female.
Further light on abnormally-directed sex-instinct is thrown by recent
analysis of abnormal domestic animals by Crew.[38] In both goats and
swine he finds that by far the commonest form of sexual abnormality is
one in which the external appearance, at least in youth, is so nearly
female as to raise no question in the mind of the casual observer;
about the time of maturity, however, male secondary sex characters
begin to develop, including male instincts; and dissection reveals
the presence of a double set of ducts--the female uterus and vagina,
the male epididymis and vas deferens, but only a single uniform
reproductive organ, and that always a testis. The simplest explanation
(although it is admittedly tentative) appears to be that the testis
has not been activated during embryonic and juvenile life, and that
therefore until puberty the animal, though really male, has been
physiologically in a neutral state, which permits the growth of the
internal apparatus proper to both sexes. Externally, the “neutral”
condition approximates more closely to the female type, and the animal
is thus first classed as a female. Some other gland is then responsible
for the second activation at puberty, and this occurs in a normal
manner.