According to archaeologists and anthropologists and geneticists, the human population went through a genetic bottleneck about 70,000 years ago. The event was probably connected to the eruption of Mt. Toba around that time. A stable, sizable population of humans, living in a hot, wet world, was decimated. Reduced to approximately 40-300 reproductive females (and a total population of perhaps 3000 humans), this bottleneck changed who we are.
A great deal of genetic diversity was lost. At such a low population, genetic drift is inevitable. For some hundreds of generations, the population slowly recovered, even as it was slowly altered, living now in a colder, drier world. We took a turn during that time, for better or worse, from who we were going to be to who we turned out to be. The humans that emerged from the catastrophic near-extinction had to be different than the humans who had existed before.
When a small group of humans left Africa, they experienced a similar bottleneck on the other side; when hunter-gatherers in Siberia crossed into the Americas, that population went through another; more recently, the settlers of Iceland created their own bottleneck of low genetic diversity. If a thousand people leave the earth on a Wall-E style ship, looking for a new home, our descendants will look different than us. It can't be helped. Only so much diversity can squeeze through.
Literature went through such a bottleneck. In fact, for most of the history of writing, literature has been stuck in one long, narrow bottleneck. Very few humans could read at any point in history. Few of those cared to write. Those who wrote did so laboriously, and copies were made by hand. During Europe's Middle Ages, new books could be counted on your hands each year (or nearly so). After the invention of Gutenberg's printing press--credited with the "democratization" of knowledge--the number of published books jumped.
The works that we read surely are a subset of all the works that might have been written and copied and published; they are a subset, in fact of the books that were written and published. We only have those which survived. Our literary heritage might have turned out very differently. When books are counted in the hundreds instead of the millions, every new book exerts undue influence.
And now, for the first time in history, millions and millions of people have a chance to write something that might persist for thousands of years. Like a human population emerging from a long bottleneck, we are experiencing an explosion of literary diversity, emerging from the constriction of the publishers and other gatekeepers. Variety that was impossible when the only books in existence were those copied by monks in a scriptorium is now commonplace. Books are available everywhere, written by authors around the world, of all ages and skills and imaginations. Like the Cambrian Explosion of 4.5 billion years ago--or the spread of hunter-gatherers from Alaska to Tierra del Fuego in a couple dozen generations--new books are filling every niche that authors can think to exploit. Most derive from the literature of our recent past, surely, but others are exotic, unique. There is no limit on what is possible.
This great flowering will undoubtedly be followed by a great pruning. But don't you wonder what books will look like in a hundred years? Where will this newest democratization of literature lead us?