By their very nature, short stories require the reader either to infer a great deal of unwritten contextual material, or to take a great deal on faith. "When It Changed" requires both; it also provides an excellent example of the economy and efficiency of an accomplished storyteller. The exposition is both revelatory and tricky. An unsuspecting reader may fail to notice that the narrator is female until halfway through the story.

The narrator refers to "my wife" and alludes to "three children between us, one of hers and two of mine." When she first describes the plague to the visiting man, she states, "We lost half our population," but only after further description of post-plague history does she explain that the lost half was all the men. The reader, at this point, must accept the premise that "the merging of ova" is biologically possible, but that is one...