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Saturday, June 1, 2013

Cultural innovation, genes, and the origin of language

Simon Fisher and Matt Ridley have argued, mainly on the basis of new DNA sequencing data, that cultural factors were far more significant in driving genetic changes in the evolutionary history of our species – such as those that led to the development of language – than was previously thought.

"The common assumption is that the emergence of behaviorally modern humans [sometime] after 200,000 years ago required – and followed – a specific biological change triggered by one or more genetic mutations."

But the "prevailing logic in the field may put the cart before the horse. The discovery of any genetic mutation that coincided with the 'human revolution' must take care to distinguish cause from effect. Supposedly momentous changes in our genome may sometimes be a consequence of cultural innovation. They may be products of culture-driven gene evolution."

Fisher and Ridley quote obvious, uncontroversial examples where culture has driven genetic change – like lactase persistence amongst dairy-farming communities, and alcohol-tolerance amongst Europeans (who generally drank more alcohol than Asians, for example).

The question of language origins is much more complex, of course, but there is mounting evidence – relating, for example, to variations in the FOXP2 gene in humans and other species – that cultural factors were the drivers of change.

FOXP2 is known to play an important role in human language abilities, but, in considering the roles of FOXP2 in human evolution, it is important to recognize that it has a deep evolutionary history.

"Animal studies indicate ancient conserved roles of this gene in patterning and plasticity of neural circuits, including those involved in integrating incoming sensory information with outgoing motor behaviors. The gene has been linked to acquisition of motor skills in mice and to auditory-guided learning of vocal repertoires in songbirds. Contributions of FOXP2 to human spoken language must have built on such ancestral functions.

"Indeed, further data from mouse models suggest that humanization of the FOXP2 protein may have altered the properties of some of the circuits in which it is expressed, perhaps those closely tied to movement sequencing and/or vocal learning.

"Given these findings, it seems unlikely that FOXP2 triggered the appearance of spoken language in a nonspeaking ancestor. It is more plausible that altered versions of this gene were able to spread through the populations in which they arose because the species was already using a communication system requiring high fidelity and high variety. If, for instance, humanized FOXP2 confers more sophisticated control of vocal sequences, this would most benefit an animal already capable of speech. Alternatively, the spread of the relevant changes may have had nothing to do with emergence of spoken language, but may have conferred selective advantages in another domain.

"FOXP2 is not the only gene associated with the human revolution. However, it illustrates that when an evolutionary mutation is identified as crucial to the human capacity for cumulative culture, this might be a consequence rather than a cause of cultural change. The smallest, most trivial new habit adopted by a hominid species could – if advantageous – have led to selection of genomic variations that sharpened that habit, be it cultural exchange, creativity, technological virtuosity, or heightened empathy.

"This viewpoint is in line with recent understanding of the human revolution as a gradual but accelerating process, in which features of behaviorally modern human beings came together piecemeal in Africa over many tens of thousands of years."

The accumulating evidence alluded to by Fisher and Ridley certainly makes Noam Chomsky's suggestion that language appeared all of a sudden and was the direct result of a genetic mutation look naïve and implausible.

But it also challenges the more mainsteam approaches still favored by many linguists who (influenced, like Chomsky, by traditional rationalism) see the human language faculty in absolute and ahistorical terms.

Descartes saw "la raison" [reason] as being "toute entière en un chacun" [entirely and equally present in each of us], and many linguists still see language in a similar – and strangely metaphysical – way.