Why are we so fascinated by identical twins?

o re twins are being born now than ever before. The number has soared in the past 20 years, according to the Twins Trust, a UK organisation which supports twins and their families, with two of the suggested factors for this being the rising use of IVF and the fact more people are starting their families later in life: multiple embryos are often implanted in IVF and older mothers tend to have elevated follicle stimulating hormone (FSH) levels, both things which make the chance of having twins more likely. However the number of identical twin births has not climbed so dramatically. The likelihood of having identical twins is about one in 250 (or 0.5%). Their relative rarity is just one of the reasons why identical twins have fascinated writers through history.

Identical twins (also called monozygotic twins) result from the fertilisation of a single egg by a single sperm, with the fertilised egg then splitting into two. Identical twins share the same DNA, the same physical features and the same sex. From an artistic perspective, the idea of two people who appear the same in every way, and are impossible to tell apart, raises many interesting questions – about the nature of the self, and what makes us the people we are, our genes or our upbringing.

Identical twins are central to the plots of two of Shakespeare's plays – Comedy of Errors and Twelfth Night – and Greco-Roman mythology is replete with them. One of the most enduring sets of identical twins in literature is in German writer Erich Kastner's novel Lottie and Lisa. Published in 1949 under the original title Das Doppelte Lottchen (The Double Lottie), it tells the story of two identical girls who meet at summer camp. "What a nerve, turning up here with your face!" says one of Lisa's friends, in disapproving terms about Lottie, when she sees them together. The girls discover they are in fact twin sisters whose parents separated them when they were babies. One has grown up with her mother in Munich, the other with her father in Vienna, and they were never told of the other's existence. They hatch a plan to swap places and meet the parent they have never met.

An enduring comedy

Kastner's book has been filmed and staged multiple times over the past 70 years – perhaps most famously as Disney movie The Parent Trap, starring Hayley Mills in the 1961 original and Lindsay Lohan in the 1998 remake – and remains a mainstay of German popular culture. It's also the basis for Identical, a new musical written by George Stiles and Anthony Drewe – the songwriting duo whose hit shows include the stage adaptation of Mary Poppins. Helmed by veteran director Trevor Nunn, Identical begins previews tonight at the Nottingham Playhouse in central England (and, if successful, will likely transfer to the West End and beyond). "This sense that there is somehow another half of you out there somewhere, [from which you have] been torn apart, is a very potent one," says Stiles of the novel's appeal. "The way the two girls are written is that they are really one complete human when they're together, but apart they're quite [contrasting] as individuals. One is quite swotty and one quite artsy. One gets good grades and one is a bit more of a troublemaker."

"Although they have identical DNA, they've been raised differently. Their characters are completely different. It's nature versus nurture," adds Drewe

Shakespeare used twins both as source of comic mistaken identity, but also, later on, yearning and loss – Dr Will Tosh

While The Parent Trap films transplanted the novel to the US and the UK, Identical retains Kastner’s original European setting and the 1950s time period. "The stage design will have the look of an old family photograph album from the 50s," explains Drewe. Without today's ease of communication, it's more plausible that the twins could have lived so long without knowledge of each other.

According to Nunn – who has previously directed both Shakespeare’s twin plays, and who says he has a fascination with twins – Kastner’s "inventive genius provides us with a narrative that takes twinship to a whole further level of comic complexity".

In the book, the girls are able to swap places and fool those around them. Even their parents can't tell them apart. This ability to play pranks, and assume the identity of the other twin, is part of what people find compelling about twins – and why mistaken identity forms the core of many twin narratives. "We're fascinated by the fact two people look so identical that they can fool people, including their parents, into not knowing which one is which," says Drewe. Though Twelfth Night's Viola and Sebastian are not technically identical twins, given their different sexes, they are apparently similar enough to baffle onlookers. "An apple, cleft in two, is not more twin than these two creatures," declares Antonio on finally seeing them together.

Though it hinges on the unarguably cruel separation of the twin girls as infants – "it's a pretty wicked thing to do," says Drewe – Kastner's book is ultimately "a story of joy and reconciliation." The duo hope the songs they have written for the show highlight "that healing is possible, even after the worst of events". The story was conceived during World War Two, and written just after it. "I think Kastner wanted to say that one can make amends if you want to," says Drewe.

Shakespeare was himself a father of non-identical twins, Judith and Hamnet, the latter of whom died aged just 11 years old, something movingly explored in Maggie O'Farrell's Booker prize-winning 2020 novel Hamnet. This might explain, says Nunn, why he was originally drawn to Plautus's play about twins, Menaechmi, on which he based Twelfth Night. Dr Will Tosh, a research fellow at Shakespeare's Globe, explains that Shakespeare used twins both "as source of comic mistaken identity, but also, later on, yearning and loss". It's tempting to "play armchair psychologist", he says, when looking at the use of twins in both Comedy of Errors and Twelfth Night, when you know that the former was written before the death of Hamnet, and Twelfth Night afterwards. The tone of the latter play was much more bittersweet, with its "fantasy of children being reunited which we also see in the later plays".

More unnerving depictions

In fictional narratives, identical twins are usually either a source of comedy or, conversely, disturbance. Doppelgängers or spirit doubles exist in many cultures – in Norse and Egyptian myth – and seeing one is often portrayed as a bad omen. One of horror's most iconic images is of the Brady girls in Stanley Kubrick's The Shining (1980), standing in the hotel hallway in their matching dresses and chanting in unison an invitation to young protagonist Danny Torrance to "come and play with us forever and ever". David Cronenberg's Dead Ringers (1988), which starred Jeremy Irons as twin gynaecologists Elliot and Beverly Mantle, and was inspired by the eerie story of real-life twin gynaecologists Stewart and Cyril Marcus, was also deeply unnerving and strange, with the Mantles using the fact no one can tell them apart for malign purposes.

The bond between twins, whether identical or not, is often depicted as intense and claustrophobic, with them sharing an almost supernatural connection with one another. An intense twin relationship is the basis for Diane Setterfield's gothic novel The Thirteenth Tale, while Curtis Sittenfeld's Sisterland features twins who have a telepathic bond. Agnieszka Smoczyńsk's upcoming film The Silent Twins, starring Letitia Wright and Tamara Lawrence, retells the story of June and Jennifer Gibbons, twin girls growing up in Wales in the 1980s who communicated only with each other, and spent many years in Broadmoor high-security psychiatric hospital. The story of the Gibbons twins has already been the basis for a book, a documentary and a stage play. Their intense connection, which ended when one of the twins died, "freeing" the other, seems to captivate people.

The stories we tell about twins tend to end in one of two ways: with the twins parted from one another, in an effort to assert their individuality, or with the twins reunited after a period of separation

In Adaptation, the 2002 film written by Charlie Kaufman and directed by Spike Jonze, Nicolas Cage plays a fictional version of Kaufman as well as his fictitious twin brother Donald, who is less neurotic and more confident with women, the epitome of all Charlie is not. It's a prime example of a twin-centred narrative that, as is often the case, is more interested in questions about identity and the self than the actual condition of being a twin. Donald is less hung up on questions of artistic originality, less self-critical, a facet of Charlie's character – so of course he has to die for Charlie to find resolution.

The musical, Identical, has cast three sets of real-life identical twins in the roles of Lottie and Lisa – "we asked them if they'd ever played pranks and they all said yes," says Drewe. However, on screen in particular, trickery is often used to allow a single actor to play both twins. Split screen was used to enable Hayley Mills to play her own sister in the 1960s, but the technology has improved since then: motion-control cameras allowed the twins in Dead Ringers to walk alongside one another, while Armie Hammer's face was digitally mapped on to another actor to allow him to play the Winklevoss twins in The Social Network. In Shakespeare's time, explains Tosh, costume, wigs and make up were used to create the illusion of sameness. "Sometimes it's less of a challenge to make two actors look identical on stage," he says. This approach was used very effectively in the Globe's 2002 "original-practices" production of Twelfth Night, first performed at Middle Temple Hall, in which Mark Rylance played Olivia, and a very young Eddie Redmayne played Viola, opposite Rhys Meredith's Sebastian; it was hard to tell the latter two actors apart. Though nowadays Viola and Sebastian are less likely to be played by two young men, so there is less concern with making them look identical.

The appeal of Kastner's book has not dimmed over the decades, with the story spreading across cultures. Adaptations of Lottie and Lisa include the 1951 Japanese film Hibari's Lullaby, Emeric Pressburger's 1953 film Twice Upon a Time – the only film he made without Michael Powell – the cheesy 1995 Hollywood movie It Takes Two, starring the Olsen twins, and 2001 Bollywood film Kuch Khatti Kuch Meethi (A Little Sour, A Little Sweet) starring the Indian film star Kajol in the role(s) of the twins. In Germany it remains a cultural touchstone. In the past few years there have been multiple stage adaptations, a TV movie, and most recently, Der Palast, a six-part German TV series directed by Uri Edel that relocated the story to 1980s Berlin and the legendary Friedrichstadt-Palast musical hall. The twins in writer Rodica Doehnert's adaptation are both young women who have grown up on different sides of the Berlin wall, and know nothing of the other’s existence. One is now a showgirl in the GDR, one a businesswoman from Bavaria. The twins represent the respective parts of a divided Germany – East and West – and their story becomes a metaphor for imminent reunification.

Drewe mentions that the plot of Lottie and Lisa is uncannily echoed in Three Identical Strangers, the 2018 documentary directed by Tim Wardle, about the lives of Edward Galland, David Kellman, and Robert Shafran, three men who only discovered they were triplets as teenagers, when one of them was mistaken for the other at college. It turned out they had been deliberately split up as infants and adopted by three separate families as part of a secret psychological study by psychiatrists Peter B Neubauer and Viola W Bernard. Initially they were thrilled to discover there were two other people out there who shared the same face as them, and enjoyed the fame it brought them, but the impact of what had been done to them took a psychological toll over time. It vividly highlights how the tendency to view identical twins – or in this case triplets – as curiosities denies them their individuality, and ignores the fact that their identicalness is only one facet of who they are.

The stories we tell about twins tend to end in one of two ways: with the twins parted from one another in an effort to assert their individuality (in the most extreme example with one twin dead), or with the twins reunited after a period of separation – with order being restored. Writing after World War Two, after a time of global turmoil, Kastner chose the more hopeful outcome, with the twins not only having found one another but having reunited their family too.