Mutants (26 page)

When we consider the male and female body we see in each, without pausing to think about it, an identity, a homology, to the other. A heart is a heart no matter which gender it sustains. Genitals are not so obvious. Their fleshy intricacies seem less versions of each other than organs of radically divergent construction which, somehow, miraculously enough, work together. Below the navel, we are mostly interested in the differences.

Anatomists, however, have other tastes. Confronted with diversity, their instinct is to simplify and unify, to search for schemes that will yoke together the most unlikely structures. This theme – the finding of homologies – runs throughout this book. But here we’re concerned with something a little different: not homology among species that have long evolved apart, but rather between the two sexes. The first reasonable account of the correspondence between male and female genitals was given in 1543 by Andreas Vesalius, the founder of a great school of Renaissance anatomists at the University of Padua. Ovaries, he argued, were equivalent to testicles. And each female fallopian tube was equivalent to a male vas deferens, as was the uterus to the scrotum, the vulva to the foreskin, while the vagina, a hollow tube, was the female version of the penis itself. For Vesalius,
then, female sexual organs were the same as those of males, but merely located internally. This theory seemed to explain everything. To give it maximum effect he illustrated it with a depiction of the vagina, cervix and uterus as male genitals in a state of perpetual semi-erection.

F
EMALE INTERNAL GENITALIA
. F
ROM
A
NDREAS
V
ESALIUS
1543
De humani corporis fabrica
.

Sex-education manuals invariably depict the male and female reproductive systems in some detail, often as two-toned tangles of labelled tubes. Unappetising though such diagrams may be, they are reasonably accurate. The reader who recalls one of the female reproductive tract will immediately observe that it bears
little resemblance to Vesalius’. A close look at his diagram, figure twenty-seven from the fifth book of
De fabrica
, shows that it is wrong in a host of details. Vesalius showed the vagina as a long, stiff, rod-like structure, but it is not; nor does it have a swelling at its tip where the glans would be. And though the scrotum may be divided into two halves (by the raphe – the point of fusion between the two foetal genital folds), the uterus is not. Some of Vesalius’ errors were surely simply made in haste. His diagram was based on the remains of a Paduan priest’s mistress that had been illegally exhumed by his students, and suggests a swift and brutal dissection. Even so, the errors are puzzling; Vesalius is usually so meticulous. One cannot help but think that the vagina he drew is as much a product of what he saw on his dissecting table as it is of his theory of the unities between male and female.

That such unities – homologies – exist is certain; it’s just that they’re quite different from what Vesalius thought they were. But Vesalius’ errors were not merely a matter of a bump more or a groove less. Allowing that it is difficult for us to see the world as a sixteenth-century anatomist did – to truly know what he did and did not know – as one looks at Vesalius’ diagram, one senses that something is awry with the whole thing; that something is simply missing. Indeed, that is so. Intimate though his knowledge of the female reproductive tract was, Vesalius failed to put his finger on the most important bit of all.

It was another Paduan anatomist, Renaldus Columbus – the same Columbus who got into trouble over an extra rib – who, in 1559, discovered what Vesalius missed: the clitoris. He called
it ‘the Sweetness of Venus’, and his description is evocative, ecstatic, and imprecise: ‘Touch it even with a little finger, semen swifter than air flows this way and that on account of the pleasure even with them unwilling … When women are eager for a man’, he continues, it becomes ‘a little harder and oblong to such a degree that it shows itself a sort of male member.’ But then he places this delightful organ in the uterus. And it is by no means clear that Columbus was really that original. Rival anatomists accused him of naming a structure that was already known to the Greeks.

Even Columbus failed to find all there was to the clitoris. In 1998, to the delight of all who have ever perceived that there is more to sex than the titillation of what is, after all, a tiny piece of flesh, the clitoris more than doubled in size. A team of Australian anatomists (headed, perhaps unsurprisingly, by a woman) working on fresh, young cadavers rather than the preserved, elderly ones that are the usual fare of medical students, revealed that the clitoris is not merely the smallish stalk of anatomy textbook and sexological dogma, but a large fork-shaped structure that surrounds the urethra and penetrates the vaginal wall.

It seemed a remarkable discovery; perhaps even the incarnation of Sigmund Freud’s much derided vaginal orgasm. In Britain, newspapers hailed the discovery and wondered how so marvellous a thing could have been missed for so long. Of course, it hadn’t been. The new, improved, clitoris is merely an old and well-described landmark that has been repositioned and reassessed. It is a structure long known as the vestibular bulbs,
two obscure lumps of spongy tissue deeply riven with blood vessels. The seventeenth-century Dutch anatomist Jan Swammerdam thought they were part of the clitoris, but the greatest of all students of the genitals, Georg Ludwig Kobelt (author of
Die Männlichen und Weiblichen Wollusts-Organe des Menschen und Einiger Saugetiere
, 1844), considered them with care and decided, on balance, that they were not. The issue turns on whether these bulbs have the kind of rich innervation that the glans clitoris and the glans penis both have. If so, then perhaps it is reasonable to label them as part of the clitoris. Nerves there are, indeed, but it is still not clear what, if any, sort of sensations they transmit. And that is surely the critical point: an expanded clitoris that is devoid of feeling is probably unworthy of the name.

C
LITORIS AND VESTIBULAR BULBS
. F
ROM
G
EORG
L
UDWIG
K
OBELT
1844
Die Männlichen und Weiblichen Wollusts-Organe des Menschen und Einiger Saugetiere.

Large or small, Columbus’s identification of the clitoris as ‘a sort of male member’ was accurate, if rather phallocentric. It solved part of the homology problem (clitoris = penis), but left the rest still obscure. What, then, was the female equivalent of the scrotum? And where was the male vagina? It was only in the nineteenth century that embryologists, tracing the development of the embryo’s organs, truly clarified what was homologous between male and female genitals and what was unique to each.

By day 28 after conception the embryo is about half a centimetre long, has four small limb-buds, and a tail. This is when the first external signs of sex appear: nothing remarkable, just a small bump between the lower limb-buds and above the tail. The bump is the genital tubercle and it is soon surrounded by two small sets of folds, one inside the other.

The genital tubercle and its two folds together make the whole of the external genitalia. (The internal genitalia – all those tubes – have other origins.) The genital tubercle rather resembles a pale, dwarfish asparagus elongating in a flesh-coloured furrow. As it grows its fate becomes obvious: a phallus – though whether a penis or a clitoris still hangs in the balance. The innermost set of folds elongate in synchrony with the tubercle to form a kind of groove beneath it, and both – tubercle and fleshy groove – nestle within the outermost folds that are, themselves, expanding to form shallow ramparts.

This is the ground-plan of gender: the developmental events common to both males and females. The differences appear only
at day 63 when the embryo is a few centimetres long and its tail is a mere docked terrier’s stump. If the embryo is male, the tubercle elongates even more and the groove that runs beneath it fuses to form a tube – the ‘genitourinary meatus’ – the viaduct of urine and semen. Below that, the larger external folds fuse to make a sack, the scrotum – but a sack that is still empty. The testes are buried deep in the abdominal wall, and will stay there until day 160 when they migrate down to the scrotum. If the embryo is female, the genital tubercle remains much as it is, but the walls of the groove that run beneath it expand and deepen and become the labia minora. The external folds swell, but do not fuse as they do in males, and become the labia majora. The labia majora continue growing until the rather minute female genital tubercle, now more properly called the clitoris, can hardly be seen.

But what of the vagina? It has no male equivalent. Part of the vagina comes from the same folds that make the labia minora, but the innermost reaches originate from a set of ducts that also make the rest of the female sex organs, but not the male’s. The homologies are now clear: penis and clitoris; scrotum and labia major; urethra and labia minora; and a vagina unique to females. Homologies that also tell us something about what happened at Saint-Jean-d’Angély around April 1838. They tell us how Abel
née
Alexina Barbin could have both a penis, albeit a small one, and a vagina, albeit a shallow one. It is as if, as a foetus, he travelled part of the route to maleness, but stopped before completing the journey. Or else that he missed the molecular signposts pointing the way.

FIFTY-FIFTY

To develop as a female is to travel a highway that is straight and wide. It is the male embryo that takes the exits; should he lose the way, he will find himself back on the route to femininity. The first signpost is the most famous of all: the Y chromosome. The Y was discovered in 1956; three years later it was identified as the master control of human gender. Within the human body, all chromosomes come in pairs matched for size and the number and kind of genes they carry. So do the sex chromosomes, but the pairing is more complex: in females, an X is paired with another X; in males an X is paired with a Y. (Normal males and females are, then, said to have XX and XY chromosomal complements respectively.) The X and the Y are physically ill-matched: the first is large, the second small. They remind one of those apparently odd couples – a large matronly woman and a small dapper man – that one sometimes finds among professionals of the Argentinean tango. The metaphor is an apt one, for no matter how implausible the pairing may seem, the two partners work smoothly together.

In sex determination, as in the tango, the Y commands and the X yields. Indeed, the proof that the Y chromosome determines sex rests upon the fact that its action is dominant over that of the X. That proof came from men who possess a Y but who also, abnormally, possess more than one X (that is, who are XXY, XXXY or even XXXXY). Such people are unambiguously male (and have perfectly normal genitalia), proving that any number of Xs are apparently powerless to curb the action of the
male-making Y. True, this power does wane slightly by adolescence, when such males frequently develop breasts and an uncertain sexual orientation. But in the womb it is clear: the presence of a Y chromosome sets a foetus decisively on the route to masculinity.

The dominant behaviour of the Y is not an arrangement that should give male chauvinists any cause for delight (or ardent feminists cause for chagrin). ‘Dominance’ refers only to the molecular rules that are used to make sex, and not to relative male and female abilities of any sort. The dominance of the Y is also probably just an accident of history. Birds also have sex chromosomes, but they have evolved quite independently of the mammalian ones and are called W and Z rather than X and Y. These avian W and Z sex chromosomes seem to work rather like those of mammals, except that it is the female of the species that has the mismatched pair of chromosomes (WZ), while males have the matched pair (ZZ). In birds, then, the chromosome that is unique to females (W) is dominant over that also found in males (Z). It might have been so in mammals, but it seems that by chance it is not.

The search for the source of the Y’s power to control gender took thirty-four years. The Y may be a dwarf among chromosomes, but it is still forty-odd million base-pairs long. Whittling this vast length of DNA down to manageable proportions took the aid of a small and unusual group of people who seemed to defy the imperious directions of the sex chromosomes. These were men who, bizarrely, seemed to lack Y chromosomes. Identified when seeking treatment for azoospermia (infertility
due to immobile sperm), they were not hermaphrodites since they had testes, perfectly good male genitalia and those alone.