Here's my best guess: we alone evolved a simple computational trick with far reaching implications for every aspect of our life, from language and mathematics to art, music and morality. The trick: the capacity to take as input any set of discrete entities and recombine them into an infinite variety of meaningful expressions.That belief is more fully articulated in this paper by Hauser, Chomsky, and Fitch. There they put it like this (from the abstract):
We hypothesize that FLN [Faculty of language—narrow sense] only includes recursion and is the only uniquely human component of the faculty of language. We further argue that FLN may have evolved for reasons other than language, hence comparative studies might look for evidence of such computations outside of the domain of communication (for example, number, navigation, and social relations).In other words, the only feature of human language that distinguishes it from all nonhuman communication systems (and, in fact, nonhuman cognition in general) is recursion, and thus recursion can explain everything about human language that we don't see in nonhuman communication systems. I imagine that seems like an oversimplification to most non-linguists, but hey, Hauser, Chomsky, and Fitch are really smart guys (Hauser was givent tenure at Harvard after being an assistant professor there, so you know he's smart), so they must have good reasons for thinking this. If you want to know them, read the paper. It's short, and fairly easy to read (which is a clear indication that Chomsky didn't do much of the writing).
I would offer you arguments against it, but like I said, people who are much smarter than me have already done so. The long counterarguments can be found in this excellent paper by Steven Pinker (who I was also hard on in the previous post, but who has Ray to bring him down to Earth in this paper) and Ray Jackendoff. Here is the gist of what they have to say about the "recursion-only hypothesis" (from the abstract):
We find the hypothesis problematic. It ignores the many aspects of grammar that are not recursive, such as phonology, morphology, case, agreement, and many properties of words. It is inconsistent with the anatomy and neural control of the human vocal tract. And it is weakened by experiments suggesting that speech perception cannot be reduced to primate audition, that word learning cannot be reduced to fact learning, and that at least one gene involved in speech and language was evolutionarily selected in the human lineage but is not specific to recursion.Some of you may not want to read the entire paper, which is not short. It's heavy on empirical evidence, contains a somewhat extended section on Chomsky's Minimalist Program, requiring at least a passing familiarity with the MP, and includes references to other works (e.g., Paul Bloom's work on word learning) that might require further reading. If you're one of these people, then you're in luck, because someone else who's smarter than me has a blog post about this really bad idea. In that post, the discovery of a hypothetical new species of humans, Homo Hemingwayensis, is announced. This species' communication system is relevant to the debate because it doesn't involve recursion:
The only thing is, the communication system of H. hemingwayensis appears to have absolutely no recursion whatsoever. "Nouns" can be modified, but only in the parallel "big bad wolf" sort of way. There is no (syntactic) clausal subordination, and no relative clauses. There are no sentential complements, though pronouns and some noun phrases ("that idea", "his argument") can be used to refer to explicit or evoked propositions. When you translate one of their stories, it comes out just like Thurber's imitation of Hemingway:
From this hypothetical, we get the following conclusion:It was Christmas eve. The grove was very quiet. No creatures were stirring in the grove. There weren’t even any rodents stirring. The baskets had been hung carefully from the upper branch. Saint Nicholas would come fill them. The children had that hope, anyhow.
There you have it. Smart people who aren't named Hauser, Chomsky, or Fitch agree with me: the "recursion-only hypothesis" is pretty silly. I have to admit, I do derive some satisfaction from the times when smart people agree with the things I say. It doesn't happen often, but when it does, you can bet that I'll post about it, just to gloat a little.
Let me say that I don't think my H. hemingwayensis scenario is very plausible. It's hard for me to believe that any creature could develop anything much like human language without at least some limited form of recursive compositionality. By my hypothesis, H. hemingwayensis does have compositional syntactic and semantic structures up to the clausal level, and analogous sorts of structures at the discourse level. Given that much, I'd be surprised not to see some use of syntactic embedding that goes at least a step or two in the direction of recursion (though whether this is implemented by fully recursive mechanisms is another matter).
But it seems preposterous to claim that syntactic recursion "is the only uniquely human component of the faculty of language". As we've observed in other contexts, sometimes it takes a really smart person to have a idea like that.