The memory of having been double remains. From time to time we seek it out. In siblings, in friends, in lovers, and finally in children of our own. The sibling is in many places the first figure to replace the parent. Perhaps just for a few minutes to begin with (“look after your brother”), and then hours or days or years.

There are few words for the kind of care a sibling gives to another. There is no word in English for losing a brother or a sister. And yet it is an experience of loss that shapes many people.