In New York Times Magazine, Susan Dominus tells the riveting story of two pairs of Colombian identical twins raised as fraternal twins — how they found each other and what happened after they met.
However, there’s a science story here, and it involves twins researcher Dr. Nancy Segal, who is studying the four brothers.
But first, a little preface from Dominus’s piece about why the study of twins is important for the rest of us:
Identical twins don’t make obvious evolutionary sense; fraternal twins at least have the benefit of genetic diversity, improving the odds that at least one might survive whatever misfortune comes their way. And yet, in their utter inexplicability, identical twins have helped elucidate our most basic understanding of why, and how, we become who we are. By studying the overlap of traits in fraternal twins (who share, on average, 50 percent of their genes) and the overlap of those traits in identical twins (who share 100 percent of their genes), scientists have, for more than a century, been trying to tease out how much variation within a population can be attributed to heredity and how much to environment.
Nancy Segal, by the way, is not one to do her studying from afar:
William had only one condition for his participation: He insisted that Segal and Montoya visit the home in which he grew up in Santander. Without that, he thought, they could never really understand who he was. He did worry, however, that if he told Segal and Montoya how long it would take to get to Santander, they would never agree to go. So he dodged and evaded whenever the subject of travel time came up. It’s a four- or five-hour drive, William would say, and then add, almost as an afterthought, that when the road could get them no closer to their destination, they would get out and walk. For how long? A little while, William would say; it might be a little muddy. How muddy? Maybe, he would suggest, it would be easier if at that point Segal traveled by horse. Would she, by any chance, rather ride a horse? Segal, a woman in her early 60s who grew up in the Bronx, said no.
And a few words about the science, quoting from Dominus:
The casual observer is fascinated by how similar identical twins are, but some geneticists are more interested in identifying all the reasons they might differ, sometimes in significant ways. Why might one identical twin be gay or transgender and not the other? Why do identical twins, born with the same DNA, sometimes die of different diseases at different times in their lives? Their environments must be different, but which aspect of their environment is the one that took their biology in a different direction? Smoking, stress, obesity — those are some of the factors that researchers have been able to link to specific changes in the expression of specific genes. They expect, in time, to find hundreds, possibly thousands, of others.
…Before she left for Bogotá, Segal contacted Jeffrey Craig, who studies epigenetics at Murdoch Childrens Research Institute in Australia, to ask if he would analyze the epigenetics of Carlos, Jorge, Wilber and William, using saliva swabs she would obtain while she was there.
Craig has analyzed the epigenetic profiles of 34 identical and fraternal twins at birth, collecting swabs from their inner cheeks. To Craig, it was noteworthy that in some cases — not many, but some — the epigenetic profile of one newborn twin was more similar to an unrelated baby than to the identical twin with whom that baby shared a womb. Structural differences in the womb could possibly account for it, Craig says — a thicker umbilical cord for one than the other (there are, in fact, two cords) or an awkward site of connection for the umbilical cord on the placenta. But he recognizes that there could be additional factors still in the realm of guesswork. Perhaps one twin is farther from the sound of the mother’s heart, its reassuring steady beat, sending that child on a slightly different life course.
Segal and Craig were eager to see the epigenetic results for the Colombian twins. Whose epigenetic profile, they wondered, would look more alike? The biologically unrelated twins who shared an environment — Segal calls them virtual twins — or the ones whose DNA was the same?
A sample of four subjects could only raise questions, not answer them. But epigenetic testing on larger samples of twins reared apart could one day provide a valuable resource for epigenetic science, says Kelly Klump, who is the co-director of the Michigan State University Twin Registry. ‘‘You can’t look at how the environment will change the function of the genome without holding constant the genome,’’ she says. ‘‘Identical twins allow you to do that.’’ Given how hard it is to find identical twins raised apart, twins researchers working in epigenetics have mostly been focusing on the identical twins who show difference. Tim Spector, a professor of genetic epidemiology at King’s College London, is generating a huge global registry for identical twins in which only one twin has, for example, diabetes or autism.
And Segal’s findings, also quoted from Dominus’s piece:
Before starting her research, Segal would not have been surprised if each young man tested similarly to his identical twin, despite their different environments. But her preliminary results, she said, show that on a number of traits, the identical twins were less alike than she initially anticipated. ‘‘I came away with a real respect for the effect of an extremely different environment,’’ Segal said.
Perhaps the results merely indicate that people raised in deeply rural environments, with little education, take tests in a wholly different manner from those who attended a university. William, who managed a small business with competence, at times seemed overwhelmed by the test. But Segal considered the young men’s story a case history that might provoke further research, inspiring others to seek out more examples of twins reared apart with significantly different upbringings, whatever they were.
Do read the whole compelling story in New York Times Magazine.