The Transmission of Language: models of biological and cultural evolution
Theories of language evolution typically attribute its unique structure to pressures acting on the genetic transmission of a language faculty and on the cultural transmission of language itself. In strongly biological accounts, natural selection acting on the genetic transmission of the language faculty is seen as the key determinant of linguistic structure, with culture relegated to a relatively minor role. Strongly cultural accounts place greater emphasis on the role of learning in shaping language, with little or no biological adaptation.
Formal modelling of the transmission of language, using mathematical or computational techniques, allows rigorous study of the impact of these two modes of transmission on the structure of language. In this thesis, computational models are used to investigate the evolution of symbolic vocabulary and compositional structure. To what extent can these aspects of language be explained in terms of purely biological or cultural evolution? Should we expect to see a fruitful interaction between these two adaptive processes in a dual transmission model?
As a first step towards addressing these questions, models which focus on the cultural transmission of language are developed. These models suggest that the conventionalised symbolic vocabulary and compositional structure of language can emerge through the adaptation of language itself in response to pressure to be learnable. This pressure arises during cultural transmission as a result of 1) the inductive bias of learners and 2) the poverty of the stimulus available to learners. Language-like systems emerge only when learners acquire their linguistic competence on the basis of sparse input and do so using learning procedures which are biased in favour of one-to-one mappings between meanings and signals. Children acquire language under precisely such circumstances.
As the second stage of inquiry, dual transmission models are developed to ascertain whether this cultural evolution of language interacts with the biological evolution of the language faculty. In these models an individual's learning bias is assumed to be genetically determined. Surprisingly, natural selection during the genetic transmission of this innate endowment does not reliably result in the development of learning biases which lead, through cultural processes, to language-like communication -- there is no synergistic interaction between biological and cultural evolution. The evolution of language may therefore best be explained in terms of cultural evolution on a domain-general or exapted innate substrate.
Full thesis (4.6MB)
Chapter 1 (Introduction)
Chapter 2 (Models of cultural transmission)
Chapter 3 (The cultural evolution of communication)
Chapter 4 (The genetic and cultural evolution of communication)
Chapter 5 (The cultural evolution of compositionality)
Chapter 6 (The evolution of compositionality in populations)
Chapter 7 (Conclusions)
Appendix A (Mathematical models of transmission)