Years ago, a woman in her 60s whom I had just met pulled out a stack of photos to show me how she had celebrated her dog’s birthday: in a neighborhood bar, with balloons and beer for the humans and a little cake made of Milk-Bones and chicken liver for the dog. Everyone, including the dog, looked like they were having a nice time. “Is this your only child?” I asked jokingly. She looked at me with a combination of scorn and pity. “He’s my dog, honey. I raised all my kids already.” I thought of that moment recently when...