The Test Said My Twin Wasn't My Twin

My brother Sam and I have been twins our whole lives. Same birthday, obviously; raised in the same cot, the same class at school, the same 'the twins' at every family gathering for thirty-one years. Fraternal twins, we were always told — non-identical, which explained why we look nothing alike, one of us fair and lanky, the other dark and square, a difference the family joked about but never questioned. Why would you question it? We were the twins. It was the most basic fact of both our lives.

We did the DNA tests as a lark, at Sam's suggestion, expecting the mild fun of comparing our heritage pie charts and confirming, with science, the twinhood we'd never had cause to doubt. The heritage results came back different in ways that were already a little odd. But it was the relatives tab that stopped us, because when the site compared us to each other, it reported that Sam and I share almost no DNA. Not sibling-level. Not even close. The shared segments of two people picked at random off the street. We are, genetically, strangers. And we have the same birthday, and were raised from birth as twins.

There is essentially one way that is possible, and we both arrived at it in the same sick silent minute: we are not related. Two babies, born the same day, somehow both ending up in the same cot, raised as twins by the same two parents — one of whom, at least, cannot be the biological parent of one of us, and possibly of either of us. A swap. An adoption folded silently into a birth. A hospital error never disclosed. Something.