I am sure that pretty much everyone has been amazed at stories like the following, of identical twins who had been separated at birth and then reunited as adults.

Thirteen days before the start of the Second World War, a 35-year-old unmarried immigrant woman gave birth slightly prematurely to identical twins at the Memorial Hospital in Piqua, Ohio and immediately put them up for adoption. The boys spent their first month together in a children’s home before Ernest and Sarah Springer adopted one – and would have adopted both had they not been told, incorrectly, that the other twin had died. Two weeks later, Jess and Lucille Lewis adopted the other baby and, when they signed the papers at the local courthouse, calling their boy James, the clerk remarked: ‘That’s what [the Springers] named their son.’ Until then they hadn’t known he was a twin.

The boys grew up 40 miles apart in middle-class Ohioan families. Although James Lewis was six when he learnt he’d been adopted, it was only in his late 30s that he began searching for his birth family at the Ohio courthouse. In 1979, the adoption agency wrote to James Springer, who was astonished by the news, because as a teenager he’d been told his twin had died at birth. He phoned Lewis and four days later they met – a nervous handshake and then beaming smiles.
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Both Jims, it transpired, had worked as deputy sheriffs, and had done stints at McDonald’s and at petrol stations; they’d both taken holidays at Pass-a-Grille beach in Florida, driving there in their light-blue Chevrolets. Each had dogs called Toy and brothers called Larry, and they’d married and divorced women called Linda, then married Bettys. They’d called their first sons James Alan/Allan. Both were good at maths and bad at spelling, loved carpentry, chewed their nails, chain-smoked Salem and drank Miller Lite beer. Both had haemorrhoids, started experiencing migraines at 18, gained 10 lb in their early 30s, and had similar heart problems and sleep patterns.

Incredible, no?

Or take a look at these two stories.

Oskar Stöhr and Jack Yufe were identical twins born in Trinidad in 1933, to a German mother and a Jewish-Romanian father, but they were separated six months later when their parents’ relationship broke down. Oskar was raised Catholic by his mother in Germany and joined the Hitler Youth. Jack was raised as a Jew in Trinidad by his father. They met briefly at 21 and were reunited at 47. Although they had very different world views, their speech patterns and food tastes were similar, and they shared idiosyncrasies, such as flushing the toilet before using it, and sneezing loudly to gain attention. The other sidebar is devoted to the ‘Giggle twins’, Daphne Goodship and Barbara Herbert, identical twins adopted into separate British families after their Finnish mother reportedly killed herself. They reunited, aged 40, in 1979. Unlike their adoptive families, they were both incessant gigglers, had a fear of heights, dyed their hair auburn, and met their husbands at town hall Christmas dances.

Stories such as these have been used to argue for the powerful influence of genes, that hereditary factors are much more powerful than the environment is shaping who we are. This in turn has led to racist eugenics theories that have caused immense harm.to groups of marginalized people, by arguing that their lot is largely due to their genes and that it is thus fairly futile to expend resources on improving them. Many of these studies have compared identical and fraternal twins separated at birth.

But as Gavin Evans (the author of the article from which the above passages were taken) argues, these arguments are spurious. Careful studies have revealed the the role if genes is much less than these astounding examples might suggest, coupled with the fact that there has been much shoddy science and outright fraud by some of the true believers in the power of genes.

But what about the cases presented above? How does one explain them? The fact is that each of our lives comprise a vast number of characteristics, events, and incidents. If we trawl through all that data we can find many things that are similar in the lives of others, and media reports are quick to seize upon these and ignore all the differences because they make a good story, and the twins themselves sometime subtly change to make their stories more similar.

More recently, two pairs of Colombian identical twins were raised as fraternal twins after being mixed up in a hospital error: one pair was raised rurally in a poor family near La Paz, the other pair grew up in a lower-middle-class family in cosmopolitan Bogotá. When they met in 2014, initial reports focused on their similarities. But when Yesika Montoya, a Colombian psychologist, and Nancy Segal, an American academic psychologist who’d once been Bouchard’s lead researcher, persuaded all four men to sign up for a batch of interviews, IQ tests and questionnaires, they discovered that the twins were even less alike than anticipated.
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Yet it is all too easy to pounce on those similarities and overstate their significance, and then brush aside differences. The Jim Twins are an example. There are clear genetic links to heart problems, migraines, weight gain, sleep patterns, nail-biting and probably to maths preference too. Other parallels can be explained at least in part by the Jims’ similar home environments, including shared holiday destinations, job overlaps and car choices. But what about both smoking Salem cigarettes, owning dogs called Toy, and having wives called Linda and Betty? Pure chance. In nearly 2,000 studies of twins raised apart, coincidences inevitably emerge, but no studies uncovered anything like the level of overlap found with the two Jims.
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Even the Jim Twins, raised by similar families, in the same part of the same state, have their own stories to tell because of their unique upbringings. Focus on these, and a different picture emerges. When they first met, they had distinct hairstyles and facial hair (one a bit Elvis, the other more Beatles) and different kinds of jobs. Their children were of different ages and most had different names. Springer stayed with his second wife, Betty, while Lewis married a third time. More significantly, they displayed marked character differences, noticeable to anyone who met them: Springer, the more loquacious of the brothers, called himself ‘more easy-going’ and said Lewis was ‘more uptight’. Lewis was reticent in public and, in private, he preferred to write down his thoughts.

There is a lot of magical thinking surrounding the study of twins and heredity, and we should be careful when we read such stories. Given a large enough dataset about the lives of two individuals, the probability of finding a dozen or so close similarities is not small.