Specializations > Language Acquisition



Mighty interesting!

http://www.ncbi.nlm.nih.gov/pmc/articles/PMC4385736/ (Open and free access)


Song-learning birds and humans share independently evolved similarities in brain pathways for vocal learning that are essential for song and speech and are not found in most other species. Comparisons of brain transcriptomes of song-learning birds and humans relative to vocal nonlearners identified convergent gene expression specializations in specific song and speech brain regions of avian vocal learners and humans. The strongest shared profiles relate bird motor and striatal song-learning nuclei, respectively, with human laryngeal motor cortex and parts of the striatum that control speech production and learning. Most of the associated genes function in motor control and brain connectivity. Thus, convergent behavior and neural connectivity for a complex trait are associated with convergent specialized expression of multiple genes.

Vocal learning is the ability to learn to produce vocalizations by imitating a model. This complex trait convergently evolved in a few lineages of mammals and birds (fig. S1). These include humans, cetaceans (whales and dolphins), pinnepeds (seals and sea lions), bats, and elephants among mammals, and songbirds, parrots, and hummingbirds among birds (1). Although nonhuman primates have a limited ability to modify their innate vocalizations, no strong evidence exists that they learn novel vocalizations (1–3). Vocal-learning species also share the presence of babbling, deafness-induced deterioration of learned vocalizations, dialects, and forebrain circuits that control production and learning of vocalizations (1, 4–6). These circuits include a corticostriatal loop and a unique direct connection from motor cortical areas [human laryngeal motor cortex (LMC) and songbird robust nucleus of the arcopallium (RA)] to brainstem vocal motor and respiratory neurons for phonation. 

Although I am not very competent in genetic literature, and therefore have only partially understood the whole paper, two questions (perhaps two NON-questions, for cleverer people than me) seem to be bothering me since I made the effort to read the article. Let me try and attempt to expose them here just in case someone wishes to answer them, even though we are in August, probably on holidays, and who the Hell cares about my (probably senile) misgivings …

(1)   If I have understood evolution theory, one thing seems to be certain: there is no previous intelligent design in the course it takes. Therefore, as in vision, species have developed different systems which have the same effect for each of them: to be aware of the world around by “seeing” it.

However, if I read the abstract right, in this case, there is a striking similarity between the genetic paths that allow humans and song-learning birds to acquire their faculty. How come? Does that mean that once a pertinent path has been found out (Ok, by chance, of course!), Nature is clever enough to admit it is a good scheme and uses it right away for other species? I can hardly believe this (an intelligent planning) to be the conclusion one should arrive at. If not, then WHAT is the correct conclusion?

(2)   In the second part of the abstract, it says that all species show some similar traits, among them, the formation of dialects. Now, the formation of dialects might be thought of as a stage in the history of a language (or of a singing system, I take it). In language, in my theoretical frame at least, there is the evident fact that when communicating, we do a lot more than coding and decoding a linguistic element, i.e., we perform a lot of inferencing on top of it. Therefore, the possible mismatch of the coded material in use when communicating does not prevent fluent communication, which, in turn, is what allows for the claim that our languages change into dialects and eventually into different languages.

If bird-songs do show dialectal differences, as the second part of the above abstract seems to state, a question arises: does communication of birds by using their songs also rely on inferencing (perhaps at a smaller scale than human language, but still…), or does it? If it does not, then, how come there are different dialects of the same bird songs?

1) This is known as convergent evolution. It's widespread, beyond any discussion of linguistics. By chance, because it happens to work well, different species sometimes converge on similar evolutionary "strategies" with similar results both in form and function. But what is unusual here is that some of the most evolved vocal systems appear to also have convergent evolution genetically. In most cases of convergent evolution, I believe, the overlap between different species is a rare case, although it does happen, among the many other cases where things differ.
Some examples that are often given include: squid eyes and human (etc.) eyes. Completely distinct evolutionary paths, but remarkably similar visual systems (fits into your example above); and marsupial mammals that look almost exactly like others around the world-- some look like dogs, some look like moles, etc. Another even broader example we could consider would be endoskeletons (vertebrates) and exoskeletons (arthropods, for example). I'm not certain they're entirely distinct from an evolutionary perspective (did vertebrates evolve out of having exoskeletons somehow?) but certainly the final result for both groups is different but structurally similar these days-- some sort of strong body-long support system for the weaker parts of the body. Whether that is remarkable, on the other hand, would be a matter of opinion.

2) Dialects:

--- Quote ---does communication of birds by using their songs also rely on inferencing (perhaps at a smaller scale than human language, but still…), or does it? If it does not, then, how come there are different dialects of the same bird songs?
--- End quote ---
What is the communicative purpose of bird songs? Inferencing is a tool used by humans to convey meanings pragmatically. If bird songs don't function the same way, I don't see why they'd need pragmatics at all really. But to the degree that any non-human species has meaningful communication, I expect inferencing is at work. Probably for birds in some cases also. Even identifying their own group/species by the sounds they hear is in some sense inferencing. That might be the primary purpose of bird song dialects: identity, as in human dialects.

Thanks, Daniel.

You are unique!

I'll have to think about your answers for a while. If I have further misgivings, I will let you know. Thanks again!


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