An only child — and the daughter of two only children who died young — Margot Livesey grew up knowing none of her other relatives and adopting a nearby family as her own. Recently, though, DNA testing led her to take a trip to Australia, where she met relatives from her mother’s side, and learned a secret about her maternal grandmother’s parentage. In this moving personal essay, she muses about the differences between adopted family and those to whom we are connected by blood, and finding fragments of ourselves in those who share our genes.