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Explore the brain/language relation,
This review is from: The Symbolic Species: The Co-Evolution of Language and the Brain (Hardcover)
Three reasons to read "The Symbolic Species". 1) Deacon describes how neuroscience is finally producing results that deal with the issue of how brains make human language possible. 2) Deacon presents a theory of brain/language co-evolution that stresses the importance of behavioral innovations that alter the human environment leading to subsequent genetic adaptation. 3) Deacon explores ways by which Philosophy of Language can be refined by incorporation of results from the scientific study of human language.
This three-fold enterprise depends on the neuroscience results discussed in Part Two of "The Symbolic Species". For example, Figure 7.8 draws our attention to the idea that prefrontal cortex is disproportionately large in the human brain. Deacon suggests that changes in the relative sizes of brain regions during human evolution is a mechanism for adaptations that allow humans to better perform language tasks. Figure 8.3 pictorially illustrates an evolutionary trend in anatomical connections towards more direct cerebral cortex control over the motor neurons that are involved in vocalizations. These examples illustrate the fact that Deacon's theory of brain/language co-evolution is heavily dependent on comparative studies of brain anatomy. Deacon tries to convince us that the major anatomical changes during human brain evolution are the precise types of changes in an ape brain that would facilitate human language behavior. According to Deacon's theory, early humans started using language as a social innovation and then the human brain changed so as to make it easier to use human language. The fact that human social interactions are a huge part of the human environment guarantees that there has to be some truth in Deacon's theory, but is it just part of a larger story?
A specific issue that Deacon touches on is the fact that non-human apes are able to learn the basics of human language simply by being exposed to a social environment where human language is being used. Why do non-human apes learn the basics of language rapidly and then stop developing more sophisticated language behavior just at the developmental stage where human children are taking off with a huge vocabulary and increasingly complex syntax? The best that Deacon's theory can suggest is that humans, unlike chimps, have had 2 million years of language use and subsequent brain evolution in response to selective pressure for larger brain regions that aid in symbolic thought. I agree that it would be astounding if certain brain regions such as the adult human prefrontal cortex is not more useful for human language tasks than is the chimp prefrontal cortex, but is this really the most important thing we need to know about the relationship between brains and language?
Is there another way of looking at the difference between human and chimp brains? One that might better inform us about the functional differences between human and chimp brains that give humans superior language skills? Deacon mentions an alternative in Chapter 6, "...the rate of human brain maturation...is prolonged compared to other primates..." In fact, most human brain growth happens after birth while most chimp brain growth happens before birth. What does this have to do with language behavior?
Perhaps everything. Why DO humans have big brains? Even though Deacon correctly points out the fact that, in the case of brains, bigger does not mean better, his whole theory ends up depending on the idea that by making some brain regions bigger, you get an ape that is better at learning human language. Deacon tries to gloss over this contradiction by assuring us that his theory is really making use of a powerful mechanism for evolving a more language-competent brain, the mechanism of "parcellation", which he claims can mechanistically explain data such as those given in Figure 8.3. Can parcellation really do all the explanatory work that his theory demands or is there a need for additional mechanisms?
Why DO humans have big brains? What if big human brains are just a side effect of some other more important aspect of brain physiology? What if larger human brain size is just a side effect of evolutionary selection for prolonged synaptic plasticity during human childhood? Maybe if we could alter a few genes in bonobos so as to prolong postnatal brain growth in certain bonobo brain regions like the anterior cingulate cortex, just maybe we would give bonobos a longer window for developing sophisticated language skills.
There is a whole tradition within neuroscience that started with behavioral studies of associative learning and led to studies of the cellular and molecular mechanisms of learning and memory. This branch of neuroscience research is almost completely ignored by Deacon. We have to wonder if Deacon's focus on neuroanatomy has provided him with a limited data set which paints his theory of brain/language co-evolution into a corner.
So my advice is that people who are interested in language should read Deacon's book, but recognize the limitations of his perspective. In the next few decades the rest of the story of how brains make human language behavior possible will come rolling in. Deacon has provided us with a working model of how to apply this hard-won knowledge of the brain to our understanding of human language, but Deacon's is just an early pass at this kind of empirically-anchored theoretical neurolingustics. Much more is yet to come. Even scientists should heed Wittgenstein's warning not to be too quick to formulate grand theories of language while so much data remains to be collected.