We have by now grown used to reports suggesting that there exist genes which encode for gayness, the tendency to put tea or milk into the cup first, and myriad other manifestations of human behaviour. The hypotheses are often interesting, but much of the work remains speculative, and some of it is highly contentious.
Going against the popular trend that sees genes behind everything are cognitive scientists Nick Chater, Florencia Reali and Morten Christiansen. In a soon to be published paper (see footnote), Chater and his colleagues show that genetic adaptation to language is highly unlikely as cultural conventions change more rapidly than genes can evolve. The biological hardware upon which language is built appears to predate the emergence of language.
A phenomenon known as the Baldwin effect, or ontogenic evolution, occurs when a biological trait becomes innate as a result of being learned. In this case, learned behaviour becomes genetically encoded over many generations, because organisms with a predisposition to acquire particular traits have an evolutionary advantage over others.
Some scientists question the very existence of the Baldwin effect, which was proposed over a hundred years ago by psychologist James Mark Baldwin in an attempt to place on a rigourous Darwinian footing the already discredited Lamarckian thesis that an organism can pass on learned behaviour directly to its offspring. Much of the controversy in evolutionary psychology and sociobiology comes down to the existence or otherwise of the Baldwin effect.
In their language and genes study, Chater and co-workers explore the circumstances under which properties of language could become genetically assimilated. By modelling the way in which genes that encode language-specific properties could have co-evolved with language, the researchers found that the genes for language could have co-evolved only within a highly stable linguistic environment. But as we know in an age in which dictionaries require updating every few years, language is by its nature highly dynamic. It is therefore unlikely that humans possess a genetic ‘language module’ that evolved through natural selection.
Chater asks whether the uniqueness of human language stems from biology or culture:
“This question is central to our understanding of what it is to be human, and has fundamental implications for the relationship between genes and culture. Our paper uncovers a paradox at the heart of theories about the evolutionary origin and genetic basis of human language – although we appear to have a genetic predisposition towards language, human language has evolved far more quickly than our genes could keep up with, suggesting that language is shaped and driven by culture rather than biology.”
Co-evolution between genes and culture can occur, and Chater cites lactose tolerance as a classic example. Tolerance to cows’ milk appears to have co-evolved with dairying, but dairying involves a stable change in the nutritional environment that positively selects the gene for lactose tolerance. In the case of language, co-evolution can occur only when language is offset by strong genetic pressures. Language then evolves to reflect pre-existing biases.
“[C]o-evolution only occurs when the language is already almost entirely genetically encoded. We conclude that slow-changing genes can drive the structure of a fast-changing language, but not the reverse.”
If universal grammar did not evolve through natural selection, then the conclusion is that language is a culturally-determined system, not a product of biological adaptation.
Further reading: “Restrictions on biological adaptation in language evolution”, Chater et al., PNAS, in press, 2009 (this paper should appear on the PNAS website as soon as the journal workers have recovered from their post-Obama inauguration hangovers).