When I was around six years old, I begged my parents for a younger sister. When she failed to materialize, I dreamed up Shelly, who showed up in family portraits I drew in art class with a frilly dress and a Pebbles ponytail. When friends came over, I told them she was with the babysitter. At school, I bragged about my bottle-feeding skills. After my teacher made a concerned phone call about my lies, my mother—a journalist and feminist activist who had me at 42—sat me on her lap, and we had a surprisingly candid conversation about why she wasn’t going to have another baby. In her late 40s, she could have copped out and told me that biology wouldn’t let her. Instead, she brushed a curl from my face and said: “We’re happy with just you.”