The main weakness of culture that is transmitted by word-of-mouth is that if the chain breaks in enough places, it could die out for good, unlike culture that can be stored in a medium.
Normally, we think of such threats to oral culture as pressures to assimilate to some other culture, such as a linguistic minority group. Growing up, the young people will pay little attention to the language of their parents, and more to the language of the world they will actually have to make it in. Slowly but surely, the language disappears.
I think, though, that there's a whole 'nother source that drains an oral culture from a community, namely when the members begin cocooning themselves from one another. We never need an outside threat to undo our culture -- we're perfectly capable of undoing it ourselves. Once we stop speaking so often to each other, there it goes.
It may not ever go quite that far -- like, we still speak to others now, but it's much more guarded than it used to be. There's an unspoken understanding not to just let it all hang out anymore. It has to be more canned, superficial, and delivered at an emotional distance. A thriving oral culture requires not being so alert, allowing spontaneity, and letting your guard down, as well as accepting it when others let theirs down. It takes two to tango.
Think of something as simple as telling jokes -- if the other person doesn't trust you or feel like being on the same wavelength as you, they might not respond at all, or give a polite social laugh, signaling that they will not spread the joke on to anyone else. And not because the joke isn't truly funny -- if you heard it from someone, they probably heard it from someone, who heard it from someone, and so on. By the time you hear it, it's passed a survival of the fittest test. For your own inventions, of course, your mileage may vary.
And don't you notice how hardly anyone tells jokes anymore? Let alone within a larger "cycle," like the dead baby jokes, Polack jokes, and blonde jokes of the not-so-distant past. You're allowed to make sarcastic remarks, rant about what pisses you off, etc., but you can't actually participate in the give-and-take of joke-telling in real life these days. I remember one day a few years ago, some of the cashiers at Whole Foods were asking customers to tell them a joke -- any joke -- as though they were begging travelers to share the details of the exotic lands they had only heard about.
Then there's the decline in legend-telling and folksong. Those were some of the first things I noticed when I stumbled onto the cultural effects of a rising vs. falling crime rate. Here are quantitative data on the death of the urban legend culture, and here is a qualitative review of the disappearance of children's subversive rhymes and songs.
There are actually even more telling signs at a more fundamental, phonological level. In a rich oral culture, the participants employ all sorts of devices to make sure that the items will be remembered later on -- they can't just be looked up, re-downloaded, or played back. As predicted by my theory that ornament is for memory, this need for easy recall leads to linguistic ornamentation in the form of repetition (with variation). The most common examples are rhyming (repetition of the sounds in the stressed vowel and everything after), alliteration (repetition of the initial consonants of stressed syllables), and reduplication (repetition of an entire syllable or word).
Right now I'm combing through a dictionary on mostly 20th-century English slang, and will have quant data to relate in a day or so. But in the meantime, try to think of how rare it is for current, commonly used slang to involve rhyming, alliteration, or reduplication. It's there, but just rare -- cockblock, Facebook friend, bling-bling... not a whole lot more.
I read through a book on youth slang as heard from 1972 to 1989, and what a reminder it was! It's hard not to find a page that didn't have some kind of repetition-for-memory device. Pedal to the metal, balls to the walls, space case, take a chill pill, bodacious bod, boom box, Suzie Sorority, stylin' and profilin', fake and bake, and on and on. Even us kids were being as creative as we could -- witness our playground game called smear the queer, and our use of metonymy in names like barf-breath, fart-face, and metal-mouth.
After the early '90s, I can only think of a couple examples, aside from the 2000s-era ones listed above. There was, Ain't no thing but a chicken wing, See ya -- wouldn't wanna be ya, Chillin' like a villain (or like Bob Dylan)... and that's about it. I read through a historical overview of 20th-C slang (organized by decade, not the dictionary mentioned earlier), and didn't come up with anything else either. There's probably a bit more from the '90s that doesn't spring to mind, but in any case way less than from the '80s.
To wrap up this scattershot examination, let's look at pop song titles. They usually are what's repeated the most, whose sounds have to pique our interest before even hearing them, and that afterward stick in our minds the most. Maybe I'll go through the decades more systematically later, but keeping for now to the recent shift, I'll just compare 1984 to 1994.
That's long enough for the decline to have really set in after the late '80s / early '90s, and it isn't even that far-apart of a time-frame. This should show just how fast the signs of a rich oral culture vanished into thin air. Those years are also emblematic of what people think of as '80s and '90s music. And most importantly, it prevents the lame technological argument that this is all due to widespread adoption of the internet and text messaging (which anyway is a free choice, and itself a sign of cocooning). The decline began well before that stuff.
Going to the Billboard Year-End Hot 100 singles chart, for 1994 we find 4 titles with repetition: Any Time Any Place, Mmm Mmm Mmm Mmm, Cantaloop (Flip Fantasia), Gin and Juice.
Turning to the good ol' days of 1984, we find 12 titles: Say Say Say, Karma Chameleon, Dancing in the Dark, Time After Time, Hard Habit to Break, Caribbean Queen, Sad Songs (Say So Much), Miss Me Blind, Dance Hall Days, Round and Round, Head Over Heels, New Moon on Monday.
Have things gotten better since 1994? No, there are only 5 titles from the 2011 year-end charts: We R Who We R, Tonight Tonight, 6 Foot 7 Foot, Barefoot Blue Jean Night, God Gave Me You.
This has only scratched the surface, but you see what I mean, jellybean. I'll have more quantitative and in-depth posts up later -- at least that's the plan, Stan. Till then, see you later, alligator.