If there is one thing that brings joy to my heart, it is charting the growth of newly invented genres. You can argue over whether trend pieces about "new adult" fiction or "baby boomer" literature are describing truly original developments or ginned-up marketing terms with no relation to measurable changes in book-buying practices (in fact, our very own Katie Baker has already done so in a very neat analysis). But at a certain point the distinction becomes meaningless; talk about "new adult" fiction long enough and Amazon will eventually dedicate a department to it.