Restrictions on biological adaptation in language evolution

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.Baldwin effect ͉ coevolution ͉ cultural evolution ͉ language acquisition

The evolution of cognitive mechanisms in response to cultural innovations

“…The real question is not whether or not it did, but rather what aspects were affected and how. For example, Chater et al have pointed out correctly that many aspects of human language change too fast for genetic evolution to respond (56). The authors used computer simulations to show that even in the presence of genetic variation, cultural conventions of language are like "moving targets" for natural selection, making the evolution of genetic adaptations to specific languages highly implausible.…”

“…The authors used computer simulations to show that even in the presence of genetic variation, cultural conventions of language are like "moving targets" for natural selection, making the evolution of genetic adaptations to specific languages highly implausible. However, although this analysis makes a convincing argument against strong nativism (the claim that there is a significant innate component to human language), it also implies that genes for language can evolve if they serve general skills for language learning that are stable over time (49,56,57). In other words, the need to learn a language may still select for many general cognitive abilities, such as better memory, computational abilities, or greater attention to verbal input.…”

What genes can't learn about language

“…However, as is well known (2, 3), this entrainment linking learning to genomic encoding works only if there is a close match between the pace of external change and genetic change, even though gene frequencies change only relatively slowly, plodding generation by generation. Applied to language evolution, the basic idea of Chater et al (1) is to use computer simulations to show that in general the linguistic regularities learners must acquire, such as whether sentences get packaged into verb-object order, e.g., eat apples, as in Mandarin, or object-verb order, e.g., apples eat, as in Hindi, can fluctuate too rapidly across generations to be captured and then encoded by the human genome as some kind of specialized ''language instinct.'' This finding runs counter to one popular view that these properties of human language were explicitly selected for, as argued in refs.…”

“…To be sure, computer simulations can still establish boundary conditions on evolvability via the Balwin-Simpson effect or set directions for further inquiry, and Chater et al (1) succeed admirably. Nonetheless, we should remain ever alert that there are always restrictions on restrictions, that neither this study nor others like it can tell us how human language actually evolved.…”

“…The right answer must therefore cut a fine line between sufficient genomic constraint guaranteeing that every child will successfully develop an adult language and sufficient lability guaranteeing that no matter where they are born each child will acquire the language of its caretakers. Now a new study in a recent issue of PNAS (1) promises to shed light on this fine balance between cultural experience and genetic entrenchment to language's design, all within the context of biological evolution. It maintains that the linguistic particulars distinguishing Mandarin from Hindi cannot have arisen as genetically encoded and selected-for adaptations via at least one common route linking evolution and learning, the BaldwinSimpson effect (2).…”