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By following the comments to another question about the evolution of Khoisan languages, I learned that there is a heated debate in Evolutionary Linguistics about the origin of language. Some quick research on Wikipedia shows that there are two major, competing hypotheses:

  • The monogenesis hypothesis, which holds that there was a single proto-language, estimated to have originated between 200,000 and 50,000 years ago.

  • The polygenesis hypothesis, according to which languages evolved as several lineages independent of one another.

What is the current state of this debate? What are the most recent (and compelling) pieces of evidence in favor of each side?

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As interesting as this questions is, it still feels like trying to infer the shape of an elephant's trunk from the skeleton. –  Mitch Oct 4 '11 at 13:59
    
Joe Martin makes the excellent point in his answer below that we know that as a bare minimum there were at least two instances of language genesis. Even if all spoken languages are related and we count them as one instance of genesis, the genesis of another language has been documented in very recent history, Nicaraguan Sign Language. So either we know this hypothesis is false, or we should change the question to ask only and specifically about spoken languages. For more see Joe's answer. –  hippietrail Apr 2 '12 at 11:44
    
There's actually two questions here: the origin of the human language faculty; the origin of spoken languages. It is quite possible that the language faculty developed once, but spoken languages developed many times (ie as with signed languages). –  Gaston Ümlaut Oct 6 '12 at 2:25
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4 Answers

up vote 15 down vote accepted

I'm not sure there really even is a "current state of the debate." Most linguists seem to view it as a question that we don't have appropriate models or analyses to address. To start, I would like to bring up some finer points:

  1. "Genetic relatedness" of language isn't even really well-defined. It is entirely possible that throughout the past many millennia, languages had a tendency to borrow very differently than today.

    • For instance, suppose you were one of a group of a dozen young women from tribe B who married into tribe C, which has about a hundred people, all at the same time. If tribe B had pronouns, and tribe C did not, but inflected verbs for person, say, only in perfective aspect, you all might start using the pronouns from tribe B; if the people in tribe C like the idea enough, they might start using them. Meanwhile, if tribe A had recently imported grammatical number from tribes elsewhere and lent it to tribe B, you might carry that with you through to tribe C.

    • What we have, in sum, is a mess. Linguists working on pidgins, creoles, and creolization may be our best bet to provide breakthroughs in this.

    • This often brings me to the analogy of genetics in a biological sense: when we look at DNA within the nucleus of a eukaryotic cell, we're definitely able to determine relatedness; however, in a colony of bacteria/organisms that may not exist anymore, the fact that one organism can "eat" a plasmid from another and maybe even splice it into its own principal DNA ring screws up the notion.

  2. "Human language" isn't really well-defined. It's easy enough to separate what is human language from what isn't, in most cases, in the present day, but the tools we've developed for that from our present-day experience probably aren't adequate to evaluate the situation, say, 300 000—40 000 years ago, or even describe it well. The burden then falls to the inquirer, what is it precisely are you wondering originated once or multiple times?

  3. What if there really was polygenesis of language, but those of the present day all come from a single source (assuming we could even define what we meant by that, and it wasn't silly)? If the last language not from the same source was, say, some North American language isolate that went extinct in the 18th century, after being sparsely documented? This leads to more interesting questions, such as what if, grammatically, it wasn't all that out-of-the-ordinary?

But as long as we're speculating, my bet is that the real answer is a mixture of mono- and polygenesis: there were many periods when tribes maintained close contact with each other, borrowing heavily across the grammatical spectrum throughout a dialect continuum for centuries, and then underwent periods of individuation, due to geographical or cultural effects; during one of these periods, perhaps you would say one of these speech patterns would finally qualify for whatever formal definition you have of "language," and during the next period of mixture, maybe it was borrowed from more than it borrowed. But then, say, a thousand years later, a dialect half a continent away, to which only a small portion of those innovations filtered, innovated enough on its own to where you could call it a "language." This whole scenario is to bear out the point that what we really have is a mess.

(I know I've employed a nonstandard usage of "dialect"; I just didn't want to use the word "language" above, for obvious reasons.)

Some references:

Polygenesis, convergence, and entropy (1996), by Lutz Edzard, takes a comparable view

In Language Polygenesis: A probabilistic model (1995), David Freedman and William Wang point out the flaws in the usual probabilistic argument for monogenesis

Addendum:

(let me know if I should create another question or something):

An article in the New York Times, World's Farmers Sowed Languages as Well as Seeds (2003), bears out the relationship between the success of the comparative method and the presence of agriculture in the cultures being studied. (This relates to my point about dialect continua/grammatical innovation/"membranes" and leads into a response to MatthewMartin's answer.)

+1 to MatthewMartin for mentioning a vital element of the "debate" Otavio Macedo was referring to. Greenberg conducted some of the most groundbreaking and notable research in linguistic taxonomy of the past hundred years, including but by no means limited to the establishment of Niger-Kordofanian and Afro-Asiatic. There always seems to be a lot of unhelpful, not-so-under-the-surface vitriol in many reactions to the Greenberg/Ruhlen research. On the other hand, when in the Amazon review of Ruhlen's book, Larry Trask says

of the 13 Basque items presented on page 65 (as 'language B'), four are wrong, and two more are not even native Basque words, but are words borrowed from Latin or Spanish. And there are also some profound problems concerning the origins and earlier forms of several of the others,

this is a factual objection, which can easily be verified. Similarly, in A Siberian link with Na-Dene languages (which I feel is the most notable finding in linguistic taxonomy of the twenty-first century so far, but that's beside the point), we read

The first person to claim a genetic link specifically between Yeniseic and Athabaskan-Tlingit (Eyak was then unrecognized as a Na-Dene language) was the Italian linguist Alfredo Trombetti (1923). Since that time, many other linguists, notably Merritt Ruhlen (1998) have repeated the same suggestion, though typically including Haida in Na-Dene

and

Merritt Ruhlen's (1998) proposed cognate sets contain several genuine cognates, among over 75% coincidental look-alikes. These are Ruhlen's comparisons for: head, stone, foot, breast, shoulder/arm, birch/birchbark, old, and burn/cook, and possibly a few others. The correct identification of cognate words for "birch/birchbark" is particularly noteworthy, as this basic vocabulary item is specific to families of the northern latitudes. The finding of these cognates, though it was impossible to confirm them as such in the absence of much more investigation, represents an important contribution,

in other words, (1) Greenberg and Ruhlen are correct that Na-Dené and Yeniseian are relatives, (2) Ruhlen's wordlist is partially correct and helpful, but (3) Haida is not part of their linguistic unit, and (4) 75% of Ruhlen's correspondences turned out to be invalid.

This is getting a little long, so I'll summarize the rest. After his Africa research, Greenberg traveled to Papua New Guinea and to South America (IIRC; if anyone can source this I'd be grateful) and collected Swadesh-type word lists from hundreds of tribes. This, too, is incredibly important research, of a nature not many have had the constitution to undertake. The results of it are, too, very important.

What's the conclusion? More research of this sort needs to be done, to get a lower error rate on the words in the lists. Sound changes need to be added back into the equation with gusto, so that we can find more correct correspondences and throw out more of the ones that don't actually hold.

And on those pronouns: they certainly do hint at the possibility of Eurasiatic (for instance) as a linguistic unit. But what if, again, there were an era where pronouns were the new hot item? Then they could all reduce to loanwords. Again, the conclusion is more research needs to be done.

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I'm pretty sure Greenberg did not collect PNG material himself, and in fact my understanding is that he collected very little primary material himself. –  Gaston Ümlaut Oct 6 '12 at 2:19
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I thought I'd follow up Daniel's excellent comment by giving an example of the problems faced by language reconstruction.

One of the best tools we have for establishing a relationship between two languages is the comparative method. This was developed in the 17th century after people started noticing some deep similarities between Sanskrit, Greek, and some other languages. They hypothesized that they all shared a common ancestor, which they called "Proto-Indo-European". By comparing the way one concept is expressed in different languages, you can come up with correspondences. If you can generalize this correspondence, you can establish a relationship between the two languages.

Let's say you discover a new island, Ba and on this island are two distinct cultures with there own distinct language, Tamo and Danu. We suspect that they share a common linguistic ancestor; the island is so isolated that we don't expect multiple migrations. Still, we can't rule it out.

We proceed by constructing a lexicon of the two languages using basic words, something called a swadesh list, which contains all the words we expect a language to have. So we've done this and developed a reliable list along with their pronunciations. It might look something like this:

 Word     Tamo     Danu 
—————————————————————————
'Man'     /tam/    /dan/
'Woman'   /tami/   /dani/
'Dog'     /kɔd/    /god/
...       ...       ... 

So on and so forth.

We immediately notice that these words look similar. 'man' is very similar in both languages: an alveolar stop, /a/, nasal, and rounded back vowel. But, there are some variations. It's a voiced stop in Danu and an unvoiced stop in Tamo. But look: we get the same pattern with 'dog', a voiced alveolar stop in Danu and an unvoiced one in Tamo. If this holds up across a lot of words, then that is strong evidence these languages share a common ancestor, which we might call 'proto-ba'.

There are lots of things that can go wrong with this. Word-borrowings, crib words, and convergent happenstance can all contrive to make two languages appear related when they are not. You can get over excited about your discovery, and start noticing similarities that aren't there. You'll want to do a lot of heavy research about the language and the people that spoke it. Who have they had contact with? Where did they come from? Have there been any major migrations that might have affected the language?

Another problem is that after a certain point, this method stops being useful. Language changes can build up over time, complicated each other or wipe each other out. Our knowledge about the language becomes less and less reliable, and we start losing important pieces to the puzzle. There is a lot of controversy about how Japanese is related to Chinese, for instance, and no one knows where Basque came from.

We'd be fighting through 50,000 years of language change, most of it without any written records and a bare sketch of population movements, and that's a conservative estimate for the age of language. It's really easy to under appreciate just how long a time that is. Proto-Indo-European, for instance, started to split up around 6000 years ago. The invention of writing is around the same age.

There are some linguists that have tried to come up with a sketch of 'proto-world', but they have been met with intense skepticism. Just google "proto-world" and click around on a few of the links.

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Merritt Ruhlen is has a good popularly accessible book on the issue and my answer is based on my reading of his book.

The anti-monogensis stance is by and large based on the proto-indo-european research agenda and their methods. It is not controversial that those techniques fall apart at about 5000 maybe even 10000 years worth of inferences. A pretty good accessible book about this research agenda and how it agrees with the archeological record for IE, "The horse, the wheel and language." The story for PIE is pretty convincing and the reconstructions almost look like a ghost of the original speakers might be able to understand it, albeit this is hardly the level of proof you get in physics or math.

Ruhlen makes the case that

  • going further back uses different techniques, e.g. focus on the evolution of pronoun systems, ignore step by step transformations, and these techniques are different than used for reconstructing PIE
  • has more modest goals, classification is a much more modest goal (i.e. will not result in a PIE type reconstruction of protoworld)
  • has turned into exercise of academics flinging feces at each other (my words, and darn if it isn't appropriate)
  • this isn't the first time the academic community reacted violently against a superfamily and then more or less accepted it, using Greenbergs research on the Bantu languages as an example.

And now for my personal opinion-- some of the most vociferous opponents are American Indian language researchers. In that community, so many competing crackpot ideas have been advanced in the past (e.g. the Indians are the lost tribe of Israel and that Amerind languages are some type of Hebrew) that the whole field has irrationally turned against the idea that Amerind languages can be rationally classified into superfamilies.

Now in other fields, genetics, archaeology and anthropology-- the researchers are coming to the same conclusions or coming to conclusions supported by the other fields. The classification of superfamilies is matching the migrations of ancient humans.

I think someone in the world of Economics (Keynes maybe?) said progress in academia is made when there are funerals. I guess that makes sense because no one wants to retract a research paper that they wrote a long while back to take into account a major shift in the understanding of the world.

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+1 for the book references. Already added to my personal reading list! –  Otavio Macedo Oct 4 '11 at 17:47
    
+1 for the quote. I did a bit of googling, and came up with "Science advances one funeral at a time." by Max Planck –  Andrew Grimm Oct 14 '11 at 13:00
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The vast majority of linguists, and especially historical linguists, do not agree with Ruhlen's methods or results. I suggest you read the review of his book by Robert Larry Trask on the Amazon page you link to. –  Gaston Ümlaut Oct 17 '11 at 5:03
    
Democracy doesn't work in science. It's a feces flinging academic fight and enjoyable to watch. Theories that seem to be saying we have no choice but to throw up our hands and say, "Well, we'll never really know" sound too much like religious mysticism to me (God works in mysterious ways, stop asking hard questions!). I'll take a theory that has a high probability of being wrong, but says something over a theory that says, "Well, we just can't know." What is to be learnt from this is the sociology of academics, not so much about the history of language. –  MatthewMartin Oct 17 '11 at 14:22
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The monogenesis hypothesis, which holds that there was a single language from which all other languages of the world came out, is false. The languages of the world include several hundred signed languages, which one can no more ignore than Austronesian or Agglutinating languages. It is beyond doubt that these signed languages arise spontaneously under certain conditions and have done so many times1,2. In at least one case, ISN of Nicaragua, researchers have documented every step of the mechanism of language creation, not “from nothing”, but by reanalyzing and reorganizing gestural communication into the hierarchical linguistic structure of human language3. At bare minimum, language provably arose without input from any existing human language, signed or spoken4, once in the 1980s and once in prehistory.

A weaker version of monogenesis for spoken languages only, would be more interesting and would:

  1. explain how this known mechanism of language genesis would generate spoken language, with its obligatory gestural components; or
  2. propose some alternative to this known mechanism, and
  3. explain why it would only operate once in the case of spoken language.

1: Goldin-Meadow, S. The resilience of language: What gesture creation in deaf children can tell us about how all children learn language. New York: Psychology Press, 2003.
2: Tomasello, M (2003) Constructing a Language: A Usage-Based Theory of Language Acquisition, Harvard University Press.
3 Hurford, James, 2001. The Origins of Grammar: Language in the Light of Evolution II. Oxford University Press.
4 Kegl, J., A. Senghas, and M. Coppola 1999 Creation through contact: Sign language emergence and sign language change in Nicaragua In M. DeGraff, (Ed.), Language Creation and Language Change: Creolization, Diachrony, and Development. Cambridge MIT Press, 179-237.

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The answer is hidden in your post: there's no reason to claim signed languages descend from spoken languages, which is why the theory is only limited to spoken: because the two evolved separately. I didn't understand your point 2. –  kamil-s Mar 28 '12 at 19:16
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Nobody suggested AFAIK that signed languages actually descend from spoken languages. But what people do suggest is that the development of ISN mirrors that of spoken creoles and therefore prima facie both modes of language will have the same sort of constraints on their genesis, and so the existence of a new sign language ab initio strongly implies that new spoken language can readily arise ab initio. –  Colin Fine Mar 30 '12 at 12:38
    
@ColinFine (I'm not taking sides in the discussion. Just a remark to your remark.) You are sure right. But I don't think any of this reasoning is necessary. After all, we do now have a language, so it must have, at some point, arisen ab initio. QED. But, it doesn't mean it must have arisen more than once. Just like life, whether it arose on Earth or came on a meteorite, only needed to appear once. I don't see how signed languages are relevant to the discussion. –  kamil-s Mar 30 '12 at 20:43
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@KamilS. Because if you broaden the scope from "Spoken language" to "Spoken or signed language" then we have evidence that it appeared more than once. The only way you can assail this is by asserting that signed language is something so different from spoken language that this is irrelevant to any question of genesis of spoken language. That position is logically perfectly self-consistent, but I think it is materially difficult to justify. –  Colin Fine Mar 31 '12 at 0:07
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@ColinFine The entire discussion, for all I know, cannot be justified materially. But the logic part is interesting. The fact alone that spoken languages now exist is evidence that they can arise ab initio. There is no necessity to include signed languages in the proof, no matter how parallel a case they are. My position was that of Ockham: if there is no necessity to assume language has arisen more than once, we shouldn't. But after I read what you wrote, I realized that if we look at it from the other end, Ockham's razor would be 'don't assume a genetic link where it can't be proven'. –  kamil-s Mar 31 '12 at 7:25
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