One afternoon in Los Angeles, Chrysta Bilton had a party; a family reunion, of sorts. Her mother, Debra, arriving in tears, told her the party was a terrible idea. Her sister, Kaitlyn, was worried a guest might steal something. It was 2019, Bilton was 34, a decade into her new understanding of what a family might look like. “Kait,” said Bilton, “if the worst thing that comes from this weekend is that one of our siblings, who we have never met, steals something from my house, I will consider it a rousing success.” And so, in they came, one by one, dozens of new brothers and sisters, all of whom shared (they learned that day in the backyard) the same big toes, the same dimple, the same inability to keep their phones charged – and all the same father. But it was more complicated than that.

Bilton arrives early to our Zoom, her large dog roaming by her feet, her small sons asleep in the room next door. She’s excited, a little nervous, to discuss the story she’s been trying to write since she was 17 – . It’s a memoir called A Normal Family, and it’s a book about anything but. “On the one hand I’ve written a story about” – she takes a deep breath – “discovering in my 20s that I had dozens, and most likely hundreds, of biological siblings growing up all over the US. And that the man I knew only as my dad, who has struggled with homelessness and drug addiction, was secretly one of the most prolific sperm donors of the California Cryobank.”

In 2005, the New York Times ran an article about two teenagers who had met on the newly launched Donor Sibling Registry, which allowed parents and offspring to search for others by sperm bank and donor number – both were the product of Donor 150. In Venice, Los Angeles, Bilton’s father, Jeffrey, saw a…