Thursday, February 12, 2009

Language evolved to fit the human brain, rather than the reverse.

I thought this PNAS article from Chater et al. on language evolution was interesting. Here are a few excerpts from their introduction, followed by their abstract (and here is a commentary in a following issue of PNAS):

...the default prediction from a Darwinian perspective on human psychological abilities is the adaptationist view, that genes for language coevolved with human language itself for the purpose of communication...A challenge for the adaptationists is to pinpoint an evolutionary mechanism by which a language module could become genetically encoded. The problem is that many of the linguistic properties purported to be included in the language module are highly abstract and have no obvious functional basis—they cannot be explained in terms of communicative effectiveness or cognitive constraints—and have even been suggested to hinder communication...

A shift from initially learned linguistic conventions to genetically encoded principles necessary to evolve a language module may appear to require Lamarckian inheritance. The Baldwin effect provides a possible Darwinian solution to this challenge, however. Baldwin proposed that characteristics that are initially learned or developed over the lifespan can become gradually encoded in the genome over many generations, because organisms with a stronger predisposition to acquire a trait have a selective advantage. Over generations, the amount of environmental exposure required to develop the trait decreases, and eventually no environmental exposure may be needed—the trait is genetically encoded.
Chater et al. modeled several different simulations of the circumstances under which a similar evolutionary mechanism could genetically assimilate properties of language in a domain-specific module. Here is their abstract:
Language acquisition and processing are governed by genetic constraints. A crucial unresolved question is how far these genetic constraints have coevolved with language, perhaps resulting in a highly specialized and species-specific language “module,” and how much language acquisition and processing redeploy preexisting cognitive machinery. In the present work, we explored the circumstances under which genes encoding language-specific properties could have coevolved with language itself. We present a theoretical model, implemented in computer simulations, of key aspects of the interaction of genes and language. Our results show that genes for language could have coevolved only with highly stable aspects of the linguistic environment; a rapidly changing linguistic environment does not provide a stable target for natural selection. Thus, a biological endowment could not coevolve with properties of language that began as learned cultural conventions, because cultural conventions change much more rapidly than genes. We argue that this rules out the possibility that arbitrary properties of language, including abstract syntactic principles governing phrase structure, case marking, and agreement, have been built into a “language module” by natural selection. The genetic basis of human language acquisition and processing did not coevolve with language, but primarily predates the emergence of language. As suggested by Darwin, the fit between language and its underlying mechanisms arose because language has evolved to fit the human brain, rather than the reverse.


Martin Walker said...

Hello, Deric.

Fascinating stuff, as always.

I have some major concerns about the conclusions being drawn by the researchers, which may simply demonstrate my ignorance:

1. Language has many structural components, surely, some of which change rapidly, others of which do not. I recently heard about a study comparing the way that parents communicate with pre-verbal infants around the world. It found a remarkable similarity and consistency in the intonations used to communicate certain basic relational information to the infant, regardless of language.

2. I'm not quite sure how to understand the conclusion that "language evolved to fit the human brain." What does that mean? Surely the components of language that are not intonation, the conceptual structures encoded in parts of speech, etc., evolved to represent our perception of the world around us.

Fundamental concepts shape the material of language, even as the words and linguistic conventions shift over time and between cultures.

Concepts aren't shaped to fit our brains... One might say more accurately our brains have adapted to recognize and organize concepts to our advantage.


Deric said...

Hello Martin,

I rather passively passed on this piece of work, and agree only in part with its perspective. I can't properly evaluate the validity of their point "Our results show that genes for language could have coevolved only with highly stable aspects of the linguistic environment; a rapidly changing linguistic environment does not provide a stable target for natural selection."....

I think Hauser, Chomsky and Fitch would argue that the genes that enable (in a human developmental context) the brain process of recursion that fundamentally distinguish human from animal 'language' are the core 'genes for language'

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