Here’s an interesting study: Apparently the life-expectancy of a bestselling fiction book has been steadily shrinking. Or to put it another way, more and more books are becoming bestsellers — but for shorter and shorter periods.

This data comes from a study conducted by Lulu.com, the online self-publishing company. It found that back in the 1960s, the average bestselling novel remained on the New York Times’ fiction list for 21.7 weeks — and only about three novels a year made it to that exalted status. But in the 2000s so far, the average bestselling novel stays on the Times’ list for a mere 3.3 weeks — but over 18 books each year do this.

In essence, the very concept of a bestseller is changing. A bestseller is no longer big, huge, rare book that dominates the national discourse for months. Instead, it’s a quick hit, a temporary talking point that flares up and then vanishes. As the CEO of Lulu.com puts it …

“The blockbuster novel is heading the way of the mayfly,” says Bob Young, CEO of Lulu.com, referring to the famously short-lived insect.

The culprit here? The 500-channel universe, and its ferocious stepchild, the Internet. The sheer volume and variety of media has so exploded in the last twenty years that it’s easier to make a quick profit aiming for a niche than aiming for the mass public: All those super-short-lived bestsellers were, I’d wager, latching their wagons either to a) some highly quotidian topic — i.e. some trend destined to vanish in a few months, taking the book with it — or b) some specialized audience that will rear up, buy the book en masse, but, being a niche, be unable to infect the broader public with their enthusiasm, thus again producing a narcotically intense but narcotically brief popularity-span for a book.

The wild card here is how the Internet, and social technologies like blogging and Google, affect popularity. As Clay Shirky puts it, the old adage in the cultural industries was “filter, then publish”: I.e. the publishers would sift through 10,000 manuscripts, pick their favorite 10, and publish those books. Ideas, in that world, come along only rarely and are thus mulled over by the public for a good long while. But in the Internet age, the paradigm is inverted: We publish, then we filter.

These days, everyone and their dog sets up a blog and expounds upon cool stuff, and the 10,000-fold torrent of ideas hits the public directly like an avalanche. Ideas aren’t rare any more. To keep from being deluged, we, the audience, do our own filtering, our own editing. We pick from amongst the online offerings by finding stuff on blogs we trust, or emails from friends, or “you may also like this” recommendations on e-commerce sites. In a publish-then-filter environment, we rely less on editors and more on tools that help us filter the opinions of our trusted friends and communities.

That’s the paradigm that’s emerging, anyway. So how is that going to affect what books become popular — and stay that way?