Thinking of buying a DNA testing kit for Christmas? You may find out more than you bargained for...

As a story-loving child more likely to be found playing detectives than the now-suspect doctors and nurses, I yearned for a family secret. My parents had both been raised with them: in my mother’s case, her dad’s Jewishness was kept hidden from her; in my father’s, paternity remained an unsolved mystery (Pétainist French Catholic priest or local milkman?).

But I wanted my own, preferably one that, hewing to the family theme, permitted a new and improved pa to step into the frame. Nowadays, I’d have done what every teenage sleuth is presumably doing and ordered a DNA testing kit online. Instead, I fired hopeful questions at my mum as I grew older: had there really been no passionate affair at the time of my conception? Even a tepid indiscretion would have sufficed—my parents met in a commune, after all.

Secrets are as synonymous with families as happiness, the murky flipside of everything that’s supposed to keep us close. Often, they fester in the deep disjuncture between the reality of family life and idealised visions of the same. They can arise from fear, shame, or tragedy, from the desire to protect another or to protect oneself. They can even be born of avoidance, as when the silence that is a family’s way of coping with conflicting values thickens over the years to become unbreachable, the topic unbroachable. When they eventually come to light, as most secrets have a way of doing, they can result in ruptured relationships and radically reconfigured family trees.

But along with so many aspects of the nuclear family, its power as a chamber of secrets is fast diminishing. The astonishing ease with which long-buried information can now be accessed plays a role. So, too, does the mass availability of genetic testing, as American author Dani Shapiro found. Three years ago, her husband told her he was ordering himself a DNA kit and asked if she’d like one. She wasn’t particularly curious—but sure, why not? That casually mailed swab led to a shocking discovery, one that made her feel as if she was looking at a stranger in the mirror. At the age of 54, she learned that the man who’d helped raise her was not in fact her biological father.

As she tells it in her memoir Inheritance, her parents struggled to conceive, eventually consulting an “outlaw” doctor whose impressive results helped couples overlook his shaky credentials. A sperm donor was recruited, but were the Shapiros privy to the secret, or had they, too, been duped?

What’s perhaps most fascinating is just how much of a surprise this is to Shapiro. Much of her parents’ story was already familiar to her—she was aware that they were older than many parents, even that they’d visited a fertility clinic. Strangers had forever been pointing out what she hadn’t allowed herself to see: that she in no way resembled her father’s side of the family.

Many secrets, it seems, are hiding in plain sight. It’s a phenomenon that the psychoanalyst Christopher Bollas calls “the unthought known,” something you know deep down but can never allow yourself to think. This active not-knowing suggests that secrets have the power to shape our lives even when they go unvoiced. We know not to ask the question, but its answer nonetheless exerts a warping presence, palpable through evasions, innuendo and rumours.

Children, especially, are hardwired to intuit when something doesn’t feel right, making the kinds of open secrets that used to be routinely kept from them uniquely corrosive. Laura Cumming wrote about this with breath-catching acuity in her recently published family memoir, On Chapel Sands. It leaves a person feeling exposed, as if others know more about their true self than they do themselves.

We find ourselves in a culture in which emotional openness is viewed as a force for moral good, and the idea that there could be such a thing as oversharing seems positively prudish. Even if we cared to try to keep secrets, we’d be hard-pressed not to leave a trail of digital breadcrumbs. From a literary viewpoint this seems a little sad. The narrative thrills to be had from the revelations that begin with the discovery of yellowing newspaper clippings hidden in attics or vintage photos depicting unknown features are irresistible. As even Shapiro admits in Inheritance, for all the trauma unleashed by that DNA test, it’s given her “a great story.”

And what of the secret-keepers? Psychotherapists largely preach that they can be set free only by the truth. They may injure a precious relationship in the process, but there will be relief in the end, they’re assured. Like so much therapy culture, it seems tinged with selfishness. In unburdening themselves, isn’t the secret-keeper merely transferring the load? What if there isn’t enough time left in a life for revelations to be fully absorbed? What of the ruined memories? The phrase let sleeping dogs lie comes to mind. As to those DNA testing kits, maybe think twice before buying them for the whole family this Christmas.