Her Fearful Symmetry
By Audrey Niffenegger
Jonathan Cape £18.99, 390 pages
FT Bookshop price: £15.19

26a
By Diana Evans
Vintage £6.99, 232 pages
FT Bookshop price: £5.59

The Twin
By Gerbrand Bakker
Translated by David Colmer
Vintage £7.99, 283 pages
FT Bookshop price: £6.39

Twin Study: Stories
By Stacey Richter
Counterpoint $14.95, 261 pages

“An apple, cleft in two, is not more twin than these two creatures.” So it is that Shakespeare presents Viola and Sebastian, his twin stars of Twelfth Night. For Shakespeare, as later for Dickens and other writers, identical and near-identical twins recur, presenting an opportunity to twist a traditional story, or a case of mistaken identity revealed only at the end.

Identical twins are a visual rhyme that we see again and again in fiction of every age and genre. Tweedledum and Tweedledee inhabit the surreal world Alice finds through Lewis Carroll’s Looking Glass; identical cousins act as a comic foil in PG Wodehouse. Twins enact gory experiments in sci-fi novels, they form invincible or evil pairings in children’s literature, and swap lives and lovers in bonkbusters.

In the real world, twins are now more common than ever before. Increased use of fertility drugs, a rise in older women giving birth and better prenatal care mean that the number of twins born in Britain and America since the 1980s has nearly doubled. One in 34 babies in the UK is a twin or triplet.

Despite their increasing prevalence, however, twins – particularly identicals – remain a subject of fascination. In what form, then, do we now find twins in fiction?

At the centre of each of four recent books is a set of identical siblings. These works all reflect on platonic love – now a less fashionable theme than romantic love – as they consider a moment that occurs in every life, twin or not, when a child nears adulthood and steps away from the family.

In the 19th century, family was a prevailing literary theme: the impact of birth was inescapable; an individual’s fortunes rose and fell with their kin, and the actions of one family member affected the whole.

Now society – and fiction too – is more atomised. Post-colonial novelists such as Salman Rushdie or Khaled Hosseini do explore the centrality of family to the self. Most modern British or American works, however, probe the choices individuals make for themselves. Even modern biography often succumbs to this trend, emphasising the “personal life” of a historic figure, rather than upbringing. Literature has shaken off the chains of family; we are all post-Freudians now.

The mini-genre of twin-lit exploits the tension between these two ways of seeing the world: familial determinism and unfettered individualism. All twin fictions are by default tales about upbringing. Yet these stories all find nature and nurture pitted against each other. The reader is asked to judge to what extent an individual’s will or imagination can triumph over their DNA. And the importance of that question is not limited to those whose genes match their sibling’s.

Audrey Niffenegger’s Her Fearful Symmetry delves into this idea through not just one but two sets of identical twins. For 21 years, Elspeth has been estranged from her double. Now on her deathbed, she writes: “It’s impossible to conjure the world without you, even though we’ve been apart for so long.” Elspeth’s dying wish is for her sister’s daughters to inherit her worldly goods – her first-edition novels, her money. This young pair, Julia and Valentina, are mirror twins: one is left-handed, the other right-handed; Valentina’s heart is on the right, the mirror of her sister.

The bestselling author of The Time Traveler’s Wife is no stranger to the fantastical storyline. And this book consciously pays homage to its historic antecedents – the title alludes to a William Blake poem; the novel’s ghost story recalls Henry James.

Yet this is also a modern work about identity. The young twins move into their aunt’s flat when they turn 21. Away from home for the first time, each character develops. In a progression repeated in the other twin novels, the two gradually pull apart.

The crippling bind of sisterly love forms the best moments in this book. “I wish I could leave her,” Valentina says of Julia. Her boyfriend replies: “You’re not married to her. You can do what you like.” But he is not a twin; he does not understand.

Can you be with another person and really be yourself? This question is at the heart of each of these books. Where other authors distinguish between romantic and platonic bonds, however, these novels deny that separation. “I’ve never been in love. With a boy,” says Julia at one point. Later she notes a friend “feels for his wife what I feel about Valentina”, wanting to be known while wanting to hide the real self in case it doesn’t match up to the image.

Her Fearful Symmetry crafts the early stages of crisis well but, as it progresses, it commits the ultimate sin for a twin novel: it fails to distinguish between two identicals. And part-way through, the narrative suddenly shifts from a love story about family to an increasingly erratic plot about haunting by the dead aunt. Niffenegger succumbs to the temptation to make this a novel about romantic love – rather than the more complex and less scrutinised bonds and boundaries of sibling love.

Niffenegger’s novel implicitly explores whether it’s possible to escape one’s family – can the self exist without its shapers? Its answer is emphatically, and tragically, “no”.

The idea recurs, to better effect, in Diana Evans’ debut, 26a. This is the story of Georgia and Bessi, born 45 minutes apart. Like Her Fearful Symmetry, 26a touches on the ideas we voyeuristically expect of identicals: the extraordinary closeness and similarities in the childhood selves. When the twins are put in different school classes, “it felt like being halved and doubled at the same time”. As adolescents they “arrived at breasts and cigarettes” together; they lose their virginity on the same night.

But the move towards self-recognition is both sharp and poignant, perhaps because Evans herself was born a twin. She has lived with the question of oneness in twoness her whole life.

The two novels have surprising similarities, particularly with regard to love. Both conclude that the platonic tie of family love can be as glorious, as troubling and as crushing as any other kind. By analysing this idea through twins rather than a romantic couple, however, there is a further question: whether a sense of self can be maintained when the bond is so close.

A French aphorism famously recounts that, in love, there is always a lover and a loved one. Is equality possible in any loving relationship? Evans and Niffenegger both conclude not. And, as any old-fashioned novel will affirm, it is loving, not being loved, that causes problems.

Early in 26a Georgia says of her twin: “She’s the best bit of me. We’re half each.” And this innocent notion plays out to a heartbreaking conclusion. The brilliance of this novel is to make us love each twin and see both sides: we seek both the comfort of Georgia loving Bessi, yet feel Bessi’s desperation to escape twindom and find her own path. This is pure, unsentimental love of the clearest kind; the result is one of the few novels I have cried at even on second reading.

Family ties have a slightly different impact in a third novel, The Twin by Dutch author Gerbrand Bakker. This is the after-story of twindom, the Waiting for Godot of the twin world: Henk dies in an accident nearly 40 years before the novel opens and we meet him only in the memories of his surviving identical brother.

After Henk’s death, Helmer is left to inhabit his twin’s life. He gives up studying in Amsterdam and returns to the family farm to help his father. He doesn’t just look like his brother, he plays the very role his brother was due to fill.

Like all these novels, The Twin cannot resist the visual cues. “The longer Henk is dead, the more I look like him, simply because there is no longer any comparing,” says Helmer.

Though there is a crisis in the twin’s relationship – when Henk falls in love – this is too distant from the novel’s present day to move us. In pace and tone, The Twin instead echoes the boredom of Helmer’s farm life now. Yet this is an interesting example of twin fiction precisely because, despite earlier divergence, one twin literally takes on the other’s life when he dies. In this it follows a storyline that real twins might find frustrating: it refutes the notion that two identical masks must yet follow distinct, inalienable paths.

Reading novels is intrinsically voyeuristic, and the ideas played out in these books are a useful prism for all our lives – we don’t need to be a twin to recognise the emotions. This idea is most explicit in “Twin Study”, a short story by American writer Stacey Richter.

In just a few pages Richter sums up many ideas twin fiction exhibits more generally. Her story follows an identical duo who, from age 12, have been “human specimens” for a California scientific study. The pair now meet every four years at “the same depressing chain hotel in Fresno to be tested, prodded, and poked”.

One sister refers to her twin as her “dark double”, recalling Niffenegger’s title. Richter also emphasises a notion we see more subtly elsewhere – that twin children seem natural and adorable, yet “adult twins seem aberrant, even to me ... a trick of genetics, a dirty trick”.

She again evokes the simultaneous horror and wonder of being a twin. The scientists consider habits, take blood and measure their brains. “They don’t ask what it’s like to wake up to one’s own double image, realizing you’ve just had the same dream about the ocean swallowing the shoreline,” she writes. “They don’t ask about the intimacy, the incredible, terrifying intimacy. Or what it’s like when it’s gone.”

And, for Richter, twindom in children is being replicated all over the world as globalisation makes different places look increasingly the same; in the suburbs she notes the same stores, the same chain restaurants serving the same chain food as elsewhere: “We’re not the only clones.”

In keeping with the setting for the story – a scientific conference – Richter directly asks why people study twins. Her protagonist’s answer? Because “they want to know what we mean for normal people”.

The study in this story is scientific but the conclusion is the same: we look at twins, at doubles, to see what we can learn about being an individual. In twin novels we are viewing life as most of us choose to experience it, in the hope that human will must dominate the genetic code we cannot alter. So we read about twins for the same reason we read any literature: to test the limits and possibilities of life – to read about ourselves.

Rosie Blau is the FT’s books editor