The oldest known depiction of a pair of conjoined twins is a statue excavated from a Neolithic shrine in Anatolia. Carved from white marble, it depicts a pair of dumpy middle-aged women joined at the hip. Three-thousand years after this statue was carved, Aborigines inscribed a memorial to a dicephalus (two heads, one body) conjoined twin on a rock that lies near what are now the outskirts of Sydney. Another two-thousand years (we are now at 700 BC), and the conjoined Molionides brothers appear in Greek geometric art. Eurytos and Cteatos by name, one is said to be the son of a god, Poseidon, the other of a mortal, King Actor. Discordant paternity notwithstanding, they have a common trunk and four arms, each of which brandishes a spear. In a Kentish parish, loaves of bread in the shape of two women locked together side by side are distributed to the poor every Easter Monday, a tradition, it is said, that dates from around the time of the Norman conquest and that commemorates a bequest made by a pair of conjoined twins who once lived there.
This is the iconographic tradition from which Shelley Wilson’s latest exhibition derives. Enter Joint Account, and you are at once a participant in that tradition of wonder and prurience – the two are scarcely separable – that have made conjoined twins the object of the artist’s gaze since the beginnings of art itself, a tradition that reached its most exuberant manifestation in Hieronymous Bosch’s Garden of Earthly Delights and its most chilling in Tod Browning’s Freaks.
But Joint Account is no freak show. It is a pathology museum, albeit one whose specimens have escaped their jars of alcohol and are now running the place. Indeed, Wilson’s medium – modelling wax – recalls the anatomical models made by Ercole Lelli, Anna Morandi, and Clemente Susini in the 18th and 19th Century and that can now be seen in all their grisly glory at La Specola in Florence. For Wilson, as for these great artist-scientists, wax captures perfectly the tortured dynamics of muscle-clad bone arranged in unnatural ways while giving the surfaces sheen and tints of human skin.
Yet there is a critical difference between the Florentines’ wax models and Wilson’s statues. Where the anatomical models were deliberately stripped of human warmth the better to display their clinical attributes, Wilson’s are imbued with the reality of life lived under the shadow of deformity. Some, such as her Cephalothoracoileopagus remind one of the terror and sadness of a young woman who has given birth to infants who die – as they must – upon reaching air. Others, such as her Craniopagus are inspired by the Pennsylvania twins, Reba and Lori Schappell – one of whom works in a laundry, while the other makes a living as a country and western singer. Her statues are, then, small essays on chance and its power to shape human lives in ways that most of us can scarcely imagine.
And they are more. For even these readings of conjoined twins – as marvels, as pathology, as essays in lived experience – do not exhaust their significance. More than any other kind of human deformity, conjoined twins have been imbued with meaning. In the 16th century, they were allegories of divine approval or wrath. Go to the Wellcome Trust’s library and ask for the magnificent manuscript of Histoires prodigieuses that its author, Pierre Boaistuau, gave to Elizabeth I of England in 1560. Here, in the greatest of the Renaissance monster-and-marvel encyclopedias you can see, amid plates of demonic creatures, wild men and fallen monarchs, one devoted to two young women standing in a field on a single pair of legs, flaming red hair falling over their shoulders, looking very much like a pair of Botticelli Venuses who have somehow become entangled in each other. For Boaistuau, however, they were not merely a pretty picture: they were allegories of political union. Another pair of Italian twins, Boaistuau notes with satisfaction, had been born on the very day that the warring city-states of Genoa and Venice had finally declared a truce – no coincidence there.
Yet the allegory-mongers weren’t to have it their own way for long. In his Essays (c. 1580) Montaigne describes a pair of conjoined twins that he encountered as they were being carted about the French countryside by their parents. He considers the idea that the children’s joined torsos and multiple limbs might be a comment on the ability of the King to unify the various factions of his realm under the rule of law, but then rejects it. He continues, ‘Those whom we call monsters are not so with God, who in the immensity of his work seeth the infinite forms therein contained.’ Conjoined twins did not reflect God’s opinion about the course of earthly affairs. They were signs of his omnipotence.
By the early eighteenth century, this humanist impulse had arrived at its logical conclusion. In 1706 Joseph-Guichard Duverney, surgeon and anatomist at the Jardin du Roi in Paris, dissected a pair of twins who were joined at the hips. Impressed by the perfection of the join, Duverney concluded that they were without doubt a testament to the ‘the richness of the Mechanics of the Creator’ who had clearly designed them so. After all, since God was responsible for the form of the embryo, He must also be responsible if it all went wrong. Indeed, deformed infants were not really the result of embryos gone wrong – they were part of His plan. Bodies, said Duverney, were like clocks. To suppose that conjoined twins could fit together so nicely without God’s intervention was as absurd as supposing that you could take two long-case clocks, crash them into each other, and expect their parts to fuse into one harmonious and working whole.
Others thought this was ridiculous. To be sure, they argued, God was ultimately responsible for the order of nature, but the notion that He had deliberately engineered defective eggs or sperm as a sort of creative flourish was absurd. If bodies were clocks, then there seemed to be a lot of clocks around that were hardly to the Clockmaker’s credit. Monsters were not evidence of divine design: they were just accidents. Just accidents? Not quite – for even as divine law receded as an explanation for the protean geometry of conjoined twins, natural law advanced.
In 1829, Ritta and Christina Parodi, a pair of Sardinian twins were brought to Paris by their parents in the hope of exhibiting them. Forbidden to do so by the Parisian authorities, the twins’ parents took them to live in a garret on the outskirts of Paris where they died from bronchitis a few months later. Their dissection at the Museum d’Histore Naturelle was one of the scientific events of the year. Heading the anatomical charge was Geoffroy Saint Hilaire, Professor at the Muséum, the most important anatomist in France. For Geoffroy, the twins were not mere abnormalities. They were, instead, the consequence of laws that regulate the construction of the human body. Conjoinedness, Geoffroy argued, was simply a reflection of what normally happens in a single embryo. The organs of an embryo develop from disparate parts that are then attracted to each other by a mysterious force rather like gravity. The intimacy of conjoined twins is caused by this same force, but misapplied so that the parts of neighbouring embryos fuse instead to one another.
Geoffroy was deeply enamoured of this deduction and, in the positivist fashion of his day, made a law of it: le loi d’affinité de soi pour soi – the law of affinity of like for like. In later years he elevated it into a fundamental law of the universe not unlike Goethe’s notion of ‘elective affinities’ to which it is related. This hubristic vision has ensured that the soi pour soi is, today, quite forgotten. This is a pity, since although Geoffroy’s law is unsatisfactorily vague, and wrong in detail, it conveys something important about how human embryos are built. It was the first scientific explanation of connectedness.
What makes twins conjoin? Aristotle, characteristically, covered the basic options. In one passage of the Generation of Animals he argues that conjoined twins come from two embryos that have fused. That, at least, is where he thought conjoined chickens (which have four wings and four legs) come from. But elsewhere he suggests that they come from one embryo that has split into two.
To modern ears his notion of how an embryo might split sounds odd, but it is a sophisticated account all of a piece with his theory of how embryos develop. Having no microscope, Aristotle knows nothing of the existence of sperm and eggs. Instead he supposes that embryos coagulate out of a mixture of menstrual fluid and semen, the semen causing the menstrual fluid to thicken rather as – to use his homely metaphor – fig juice causes milk to curdle when one makes cheese. Sometimes, says Aristotle, there is simply too much of the pre-embryonic mix. If there is only a little too much, you get infants with extra or unusually large parts such as six fingers or an overdeveloped leg; more again, and you get conjoined twins; even more mix, separate twins. He uses a beautiful image to describe how the mix separates to make two individuals. They are, he says, the result of a force in the womb like falling water: ‘…as the water in rivers is carried along with a certain motion, if it dash against anything two systems come into being out of one, each retaining the same motion; the same thing happens with the embryo’.
Until recently, the origin of conjoined twins has been debated in much the terms that Aristotle used: they are the result either of fusion or fission. Most medical textbooks plump for the latter. Monozygotic (identical) twins, the argument goes, are manifestly the products of one embryo that has accidentally split into two; and if an embryo can split completely, surely it can split partially as well. This argument has the attraction of simplicity. It is also true that conjoined twins are nearly always monozygotic – they originate from a single egg fertilised by a single sperm. The latest ideas suggest, however, that Aristotle’s dichotomy – fission or fusion – is illusory. The making of conjoined twins is, first, a matter of making two embryos out of one, and then of gluing them together. Moreover, the way in which two embryos are made out of one is nothing so crude as some sort of mechanical splitting of the embryo. It is, instead, something more subtle and interesting.
Just what was discovered by a young German scientist in 1923. The experiment she carried out was deceptively simple: she transplanted a piece of tissue from one newt embryo onto another. The results, however, were momentous, for when Hilda Pröscholdt’s surgically enhanced newt embryos grew up she found that instead of one newt she had two – and they were joined together. She had made conjoined-twin newts.
Hilda Pröscholdt had discovered the “organizer”. A tiny piece of tissue located near the embryo’s future anus, it is the source of order in the embryo. It tells the surrounding tissues what to become: a head or a tail, a back or a front. It does so by secreting a plethora of molecules that signal to the surrounding cells information about where they are and so what they should become. It is something that every vertebrate embryo – newt, fish, chicken, mouse, human – has, indeed must have, if it is to have all its parts in the right place. Human conjoined twins are probably the result of a natural accident that simulates what Pröscholdt did by surgery. They are very likely the result of an embryo that has two organizers instead of the usual one. Why the organizer should sometimes double itself is a mystery – human conjoined twins occur so rarely (about one in every hundred-thousand live births) and unpredictably that there is no obvious way to find out – and yet it’s easy to see in principle how it could happen. Where Pröcholdt gave her embryos that extra anomalous organizer by some deft surgical manipulation, modern biologists do it by simply switching on various “master-control” genes in their embryos. The making of two embryos out of one may, therefore, be simply a matter of one of these master control genes being turned on the embryo where it normally is not.
Whatever the ultimate cause of conjoined twins, the ‘two-organiser’ theory, while a neatly plausible account of how to get two embryos out of one is, in itself, not a complete explanation for their existence. The theory has nothing to say about their essential feature: the fact that they are glued together. For that we need something like Geoffroy’s soi pour soi – and we have it. For, just as Geoffroy inferred, there is a law of attraction at work in the embryo. As the embryo develops, its various organ primordia must find each other and fuse (that they do so almost unerringly is one of the marvels of embryogenesis). This glueing-together is not, however, the result of some gravitational force, but instead comes from the action of thousands of different molecules that are attached to the surface of cells and are, as it were, signals of their affiliation, that permit other cells to recognise them as being of like kind. These are the cell-adhesion molecules; molecular biologists speak of them as the Velcro of the body: weak individually, but collectively strong. It is their action, albeit misapplied, that glues conjoined twins together in the womb. And their power is startling – you can see it in Shelley Wilson’s Cephalothoracoileopagus. Oriented belly to belly, their faces are deflected 90o relative to their torsos so that they gaze, Janus-like, in opposite directions. What is remarkable about these children is that each apparent face is composed of half of one child’s face fused to the opposite half of his brother’s. The developing noses, lips, jaws, and brains of these two children have found each other and fused perfectly – twice.
There is one final source of meaning that can be sought in Joint Account – and its presence in the Old Operating Theatre tells us what it is. Today, conjoined twins are not examined for their allegorical significance, nor even for the biological insights that they can yield; they are, instead, a medical and legal matter. In 1974 Clara and Altagracia Rodriguez became the first conjoined twins to undergo successful surgical separation. Since then, the birth of each new pair – Mpho and Mphonyana (b. 1988, South Africa), Katie and Eilish (b. 1989, Ireland), Angela and Amy (b. 1993, USA), Joseph and Luka (b. 1997, South Africa), Maria Teresa and Maria de Jesus (b. 2002, Guatemala) – to name but a few, has been the occasion of a miniature drama in which surgeons, judges and parents have been called upon to play the part of Solomon. Should conjoined twins be separated? Increasingly, many think not – at least not when both twins have a reasonable chance of survival. They argue that surgeons have been too enraptured by the technical problems that conjoined twins present; too eager to exhibit their skills by separating the inseparable. Lori Schappell is quite clear on the matter: “We never wanted to be separated, we never do want to be separated and our families never ever wanted us separated because we fully believe that God made us this way and He had a purpose for us and you do not ruin what God has made.” Any biologist would substitute “nature” for Lori’s “God”. Even so, looking at Shelley Wilson’s Joint Account, it’s easy to see what she means.