Languages change over time, but how fast? Let's say you fall into a coma hearing your
language spoken all around you. You snap awake in the same place but at a
different time. They're still speaking your language, but
you can't understand a word. How long were you out? How long can a language last before it becomes
unrecognizable? Last time we met an eccentric Australian tongue
called Dyirbal, a language where nouns can be edible or harmful, where you have to talk
completely differently around your in-laws, and where speaking vaguely is considered a
serious flaw. And they don't even have a word for language! At least, it used to be that way, because
when linguists came back to visit the Dyirbalŋan decades later, their language had changed. Then we heard from Swadesh, who argued that,
actually, no, all languages change at the same pace, replacing core vocabulary at a
constant rate, keeping over 80% of their most basic words after 1000 years. Swadesh then used his vocabulary lists and
calculations to draw a line marking how long we'd expect to wait before dialects of a single
language evolve into separate tongues. A line in the sand. The elusive moment of change itself. Spot any problems with this idea? These researchers sure did. They grabbed their Swadesh lists and pointed
them at two sibling languages: Norwegian and Icelandic. The basic question they wanted Swadesh to
answer was this: how many years had passed between Old Norse and Norwegian, and how many
between Old Norse and Icelandic? Looking at word lists for replacement, plugging
in that stable rate assumption, it looks like Norwegian diverged 1000 years ago, not a bad
estimate actually, while Modern Icelandic is... 200 something years old. In other words, no one should be speaking
Icelandic right now. Call up Iceland! Your language is a mistake. The numbers don't lie. Today, thanks to debunkings like this, and
the fact that Icelandic exists, historical linguists accept that the rate of language
change varies, and for various reasons. According to this paper, one factor could
be population size. In a computer simulation, smaller populations
borrowed and replaced words faster than bigger communities. The author of that Dyirbal grammar, Dixon
himself, proposed another factor. He called Swadesh's idea "the chimera of glottochronology"
and argued instead that languages have long, stable periods, but then change in punctuated
bursts during moments of social upheaval. So is that why Dyirbal changed so much so
fast? A small population and a quick punctuation? Well, a careful look at the switch from Traditional
Dyirbal to Young Dyirbal suggests another variable, the biggest reason why the language
changed so much in just decades: language death. A few decades before Dixon's grammar, about
30 Dyirbalŋan still lived around the upper Tully River, hanging on to the old ways. But these days, it seems like nobody is learning
Dyirbal, threatening even Young Dyirbal with extinction. It's not just assimilating to Australian English
or turning into a bare-bones pidgin or creole. This researcher tells us it's not that simple. Behind the steep change from Traditional Dyirbal
to Young Dyirbal was a smooth oldest-to-youngest dropoff. Dyirbal has been dying its own death, and
language death is its own variable. With all these complexities, how long do we
have to be out before we wake up to a brand new language? It depends. Some tongues seem to keep their shape over
1000 years, others do indeed change quickly within centuries. But take another look at the question we started
with: how long can a language last before it becomes unrecognizable? Not unintelligible to earlier speakers. Utterly unrecognizable. See, even if a time-traveling Dyirbal speaker
couldn't understand the language, they might be still able to pick out familiar words. How do we know this will happen? Because it has happened. This isn't the first time Dyirbal has evolved. We got a glimpse of its past changes in part
one when we met a relative of Dyirbal where the word for dog is "dog". That word took linguistic know-how to prove
it was actually related to Dyirbal, not English, but other patterns among Australian languages
are easier to recognize. Whatever you think about Swadesh lists, here's
a fun use for them. Compare basic vocabulary from a bunch of Australian
languages and look for cognates. Comparing cognates and sound changes and grammar,
linguists focusing on Australian languages looked far back beyond Dyirbal to recover
its entire family: the Pama-Nyungan languages. There is dissent, Dixon in particular came
to reject this grouping, but the consensus is that Pama-Nyungan constitutes the largest
family on the continent by far. Using various lines of evidence, Pama-Nyungan
is held to be around 4,000 to 5,000 years old. Which is intriguing. Because look what happens when we estimate
the ages of other language families: we get similar time depths. The one aberration here seems to be Proto-Afro-Asiatic,
a story for another time. Some historical linguists warn that they don't
do dates, but some that do see a limit here: comparing languages can only take us several
thousand years into the past. Of course, in my Tower of Babel first language
video, we did meet some mavericks who dare to go even further. So, how long should we keep that hypothetical
linguistics patient under to make sure they wake up to a changed language? Well, within hundreds of years we could expect
degraded intelligibility, with handwaving on dates and how understandable it will be. But within many thousands of years, even distant
traces of the language may have dissolved. Though keep your apologies handy in case this
answer is too vague for the Dyirbalŋan. Hah. Stick around and subscribe for language.
The way this video presents its conclusion is weird. The implication that 5,000 years is a magic number glosses over the fact that it's dependent on the available data. Proto-Basque is only 1,000 years old, because the Basque family is not very diverse. On the other hand, Proto-Afro-Asiatic is old as dirt because there are Afro-Asiatic texts dating back 4,600 years (and because of somewhat lax ideas of what constitutes an identifiable Afro-Asiatic language, but let's not get into that).
At best, the way to keep 5,000 years as a magic number (and you have to to some extent, to explain why many large language families are that age) is to explain it as the maximum amount of time that a language family can remain diverse enough for its proto-language to be reconstructible from its present-day spoken languages. In other words, 5,000 years is a sort of asymptote on reconstructibility parametrized by the ways in which the world limits the spread of cultures and by the power of our reconstructive methods, with Afro-Asiatic's longevity explained away as "cheating" with very old written records.
One "testable" (in a very weak sense of the word) prediction that this model makes is that, given that Indo-European languages spread unusually far and wide in the Early Modern period (even further and wider than in the original Indo-European period), we'd expect the languages that proliferated during that time period to eventually remain reconstructible longer than the typical amount of time. But this is a prediction for over 4,500 years in the future, so the "test" won't have results until then, and who knows what sort of intervening Early Modern Era-esque stuff will happen in the meantime anyway. (Especially given the recent innovation of the internet.)
One problem with it is that it would predict an earlier date for PIE, since we also have very old texts for IE languages (dating back to 3,900 years ago). But between the facts that the Anatolian languages are highly divergent, that the date for PIE is pinned down by archaeology compared to the vagueness of the date for PAA, that PIE is older than 5,000 years anyway, that there are other factors influencing the AA grouping, that PAA isn't really reconstructible anyway, and that the model only predicts a maximum time, not a specific time, it does not seem like a large problem.
In any case, I enjoyed learning that progressive language death can accelerate language change, and I wish the video had gotten into that more with more specific sorts of changes, with examples from Dyirbal and other dying languages.