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.

I for one welcome these developments: there is always more room at the genre table. Ten years ago the only hip-hopera mainstream America knew was Carmen; now there is an embarrassment of riches, hip-hoperatically speaking. The important thing to do is compare them and declare a winner, so that each generation remains always at the other's throat.

Can this new genre be pegged to the success of young adult literature?

Coming of old age:

A new genre is born, a pendant to Young Adult literature, with one difference: Baby Boomer novels address "coming of old age" issues just as Young Adult novels are concerned with just coming of age.

New adult:

They've labeled this category "new adult" - which some winkingly describe as Harry Potter meets "50 Shades of Grey" - and say it is aimed at 18-to-25-year-olds, the age group right above young adult.

Boomer lit isn't "just like" coming of age literature: it's better. Point Boomers.

Is the market growing? Extra points for vagueness.

Coming of old age:

With a huge and growing market of some 70 million boomers - technically, all those born between 1946 and 1964 - Hollywood was the first to notice the change in its audience.

New adult:

Although most booksellers PW spoke to had not heard the term "new adult," there are some who are recognizing the growing swath of books that are sort of young adult, but not really.

"There are some...but not really." Masterfully opaque. Point new adults!

Can you draw unsubstantiated comparisons with existing media properties?

Coming of old age:

Recent Baby Boomer movies, such as RED, Hope Springs, or The Best Exotic Marigold Hotel, have all been smashing successes.

Yet most movies are based on books and perhaps, historically, the first book that led to a hugely successful movie, was Louis Begley's About Schmidt in 2002. The movie was only loosely based on the novel, but Jack Nicholson's star performance made it memorable. And it certainly opened the way to the new Baby Boomer genre.

New adult:

The goal is to retain young readers who have loyally worked their way through series like Harry Potter, "The Hunger Games" and "Twilight."

Coming of old age goes for a reach, dropping unrelated movie titles and a 10-year-old film in the same breath, but Harry Potter/Hunger Games/Twilight makes for an unbeatable hat trick. Point new adults.

Is it sexy? Make it sexy.

Coming of old age:

Now boomers have moved on. They are 50+, still vigorous and dynamic, and their interests have also changed. Fiction needs to follow them and provide protagonists who deal with issues of concern to baby boomers.

New adults:

In the "Twilight" books, for instance, readers are kept out of the bedroom when Bella and Edward, the endlessly yearning lead characters, finally consummate their relationship.

Providing more mature material, publishers reason, is a good way to maintain devotion to books among the teenagers who are scooping up young-adult fiction and making it the most popular category in literature, with a crossover readership that is also attracting millions of adults.

Coming of age starts out promising with "vigorous" and "dynamic" but fails to follow through with specifics. A "still sexual" or "unapologetically frank" could have tipped the scales, but this is another point for new adults.

Who's buying more books?

Coming of old age:

Generation Y, readers born between 1979 and 1989, spent the most money on books in 2011, taking over the book-buying leadership from baby boomers, according to Bowker's just released 2012 U.S. Book Consumer Demographics & Buying Behaviors Annual Review.

New adults:

Generation Y spending more money on expensive titles for school or work than other age groups. Generation Y was the only age group whose spending was higher than its proportion of the overall population.

At first glance it seems that Millenials have clearly outstripped Boomers as a purchasing power bloc, but then Publisher's Weekly slips the old knife between the ribs: they're just buying more textbooks. Point Boomers.

Victors by a single point, the coming-of-old-age crowd can enjoy their victory in the wary knowledge that new adults are coming for them. Heavy is the head that wears the crown.

Representative titles in the definitely-real New Adult genre include Hahaha what's money?? where did my dreams go, A Shot-by-Shot Recap of Every Show That Ever Aired On Nickelodeon Between 1987 and 1998, Recession Pies, and Kickin' It With Kidults. Kickin' It With Kidults is a four-thousand-page book that lists every person between the age of 23 and 27 living in America in order of how much they still owe in student loans. It will be sold exclusively in gelato shops.

Representative titles in the coming-of-old-age genre include My Marriage Isn't Very Good Anymore But Maybe I Expected Too Much, I Don't Know, It's Not Bad Really I Guess, Just Empty, I Will Never Be Able To Retire, Raising Kidults With Devices and a collection of printed-out TED talk transcripts called [Untitled Fixing Africa With Innovation Project].

[Image via AP]