Bob Berwick sent me this article
on songbird and human brains. The paper is a pretty hard slog form someone with
my meager biological and computational talents, however, the abstract is
relatively comprehensible even to someone like me. Plus, Bob was good enough to
hold my hand and explain what the whole thing meant. Here’s how Bob explained
the results to me:
The paper appeared in Science
December 12, the lead author Andreas Pfenning, was in Erich Jarvis’ bird lab at
Duke.[1]
As its title says, it’s about the convergence of specialized gene
transcriptional factors in vocal learners – birds vs. us/
They sifted through thousands of genes and gene expression profiles in
the brains of songbirds, parrot, hummingbird, dove, quail, macaque, and us,
attempting to correlate distinctive expression profiles against a sophisticated
hierarchical decomposition of known brain anatomy in all the species,
attempting to find out whether subregions where certain genes were expressed
more highly matched up to each other across species lines in the case of vocal
learners (songbirds, parrot, hummingbird, us) as opposed to non-vocal learners
(dove, quail, macaque). And the answer
was Yes: the same transcriptional profiles could be aligned across all vocal
learners, but not in vocal learners vs. non-vocal learners.
I am lucky because that first
author, who did a lot of the computational work as part of his PhD under
Jarvis, Andreas Pfenning, is now a post-doc here at MIT working on genomics,
just 2 floors below me. So I had him walk me through the article and this is
what he told me: The bottom line (see Fig. 1 and Table 1 of the article) is
that the sets of regulatory elements – stuff that gets genes “read”
(transcribed) faster or slower in song learning birds and humans are the same
across both sets of species – about 50 or so genes being regulated. That’s
pretty amazing considering that birds and us are separated by at least 310
million years from a common ancestor. That’s a lot of evolutionary time. Yet, both sets of species converged on the
same solution for vocal learning. Now, it might be that there are just not that
many ways to build a vocal learning system and it’s all been highly conserved,
a lot like the eye. And going a bit further, it’s not hard to imagine that all
vertebrates have the same basic toolkit for vocal learning, and then it’s
switched on by just a few regulatory changes and voilà, you’ve got a song to
sing. Now as to why it’s not switched on
in other primates – who knows? But what it does hint is that it might not take
that long to get the “input/output” peripheral device built, a key part of “externalization”. And if so, then maybe that doesn’t take a lot
of gene tweaking – perhaps as few as 1 or 2 genes out of the 50 – and it all
gets done a lot faster than updating the MBTA subway trains (currently 1/2
disabled because they are more than 50 years old and run on DC current. Sorry,
I couldn’t help myself, there’s nearly 2 meters of snow here and the mass
transit has broken down). So, evolving externalization might not be as hard as
Chomsky has thought. And there you go:
something for us to think about for evolang.
Oh – they found an intriguing nonassociation:
between the birds’ Pallium or HVC areas, and their putative counterparts in
human, Broca’s and Wernicke’s areas. Big caveat 1: all these results are associations – correlation, not
causation. There’s a lot of work now to
figure out what they actual “genetic circuitry” is – what actually causes what,
what the implicated genes actually do, etc. They do a bit of that in the full
paper, and there are several more interesting results that I won’t cover
here. Big caveat 2: just because they
didn’t find associations, doesn’t mean they aren’t there, as they say.
So, it looks increasingly likely
that songbird brains are goodish neuro models for human brains when it comes to
the study of vocalization. Berwick, Beckers, Okanoya and Bolhuis
already noted the “linguistic” similarities between bird song and
phonology. It now looks like this behavioral convergence might rest on
convergence in brain organization rooted in exploitation of the same genetic
mechanisms.
As Bob notes, this sure looks like (but note his caution
here) another case of the eyeless
gene. In other words, it looks like there is effectively one way to get
vocalization off the ground biologically and all vocal species use the same
basic genetic tricks to get this capacity in place. Moreover, given that
vocalizers are scattered across phyla and clades it also looks like this trick
is a biological option that can be pressed into service under the right
conditions (whatever these happen to be, and, from what I can tell, what these
conditions are is quite obscure. After all, not all birds sing, nor all apes, nor… And the question is why not if
indeed this really is an available option. In other words, what are the down
sides of vocalization such that every animal doesn’t blather away all the
time?).
To my mind, this makes Chomsky’s conjecture that Natural
Language is Meaning with sound
(rather than meaning and sound) quite
attractive.[2]
Vocalization is something that natural selection can call on under the right
circumstances, and coupling a recursive FL (which enhances thought) to an
externalization mechanism which would leverage this capacity by allowing
communication of these thoughts, seems like a plausible candidate for a “right
circumstance” (all of this is very
speculative, of course). Note, that given the spotted ubiquity of vocalization
(i.e. across very different animals: birds, mice, whales, humans) it would seem
that the causal line that Chomsky suggested (Recursion then externalization)
makes sense. At the very least, the capacity to communicate (if we identify
this with vocalization) does not bring with it the kind of grammatical system
we find in humans. Biologically, it seems, there is a plausible story taking
you from Merge to externalization, but none from externalization to Merge. Or,
to put this another way: that humans vocalize is not that surprising given that
this is the sort of capacity that seems to be just sitting there genetically
for the taking. What is not just there for the taking is hierarchical
recursion. Given the latter, there is plausibly further evolutionary utility to
being able to vocalize. Hence, Chomsky’s conjecture: Merge first,
externalization second.
Of course, if this is correct, it lends some support for the
view that core parts of FL did not arise for communicative ends or in response
to the advantages for communication. Communication was an add on with core
properties of FL arising first and then the extra benefits of being able to communicate
the thoughts that the newly e”Merge”nt mechanisms made available coming on line
manifest. To repeat, all of this is highly speculative, but it is intriguing to
see that one standard mechanism for communication (i.e. vocalization) seems is
effectively the same system in birds and people (and, I would bet, mice and
whales and…) and that it seems to be latently sitting there ready for service.
Interesting stuff. Thx Bob.
