Although languages vary, they share many universal structural properties. Where do these universals come from? A great deal of research has proceeded under the assumption that this is essentially a biological question: that languages have the structure they do because of our innate faculty for acquiring and processing language.They suggest:
...that there are serious problems with this orthodox evolutionary/biolinguistic approach. It treats language as arising from two adaptive systems, individual learning and biological evolution, but in doing so misses a third: cultural transmission. The surprising consequences of taking all three adaptive systems into account are that strong universals need not arise from strong innate biases, that adaptation does not necessarily imply natural selection, and that cultural transmission may reduce the selection pressure on innate learning mechanisms. Our conclusions call into question the existence of strongly constraining biological predispositions for language, and the prominence of adaptationist explanations for the structural properties of languages.Here are two useful figures from the paper, and the details of the Bayesian model they use you can find in the PDF of the article.
Fig. 1. (Click to enlarge) The structure of language arises from the interactions between three complex adaptive systems. As individuals, we acquire language using learning mechanisms that are part of our biological endowment (characterized in this paper in terms of prior bias). This learning machinery acts as the mechanism by which language is transmitted culturally through a population of individuals over time. Ultimately, this process of cultural transmission leads to a set of language universals (which can be expressed as a distribution over types of languages). The relationship between learning machinery and consequent universals is nontrivial but can be uncovered using the framework developed here. Finally, the structure of languages that emerge from this process will affect the fitness of individuals using those languages, which in turn will lead to the biological evolution of language learners, closing the loop of interactions.
Fig. 2. (Click to enlarge). The link between biological predispositions and language structure. Genes (in combination with the nonlinguistic environment) give rise to mechanisms for learning and processing language. These determine our innate predispositions with respect to language (our prior linguistic bias). Bias is a property of an individual, but the (universal) structure of human language emerges from the interaction of many individuals over time. Therefore, cultural transmission bridges the link between bias and universals. Although genes code for bias, biological fitness will in part be governed by the extended phenotype (i.e., language structure). To understand language evolution, we must understand this linking mechanism.