Modelling the transition to complex, culturally transmitted communication
Ritchie, Graham R S
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Human language is undoubtedly one of the most complex and powerful communication systems to have evolved on Earth. Study of the evolution of this behaviour is made difficult by the lack of comparable communication systems elsewhere in the animal kingdom, and by the fact that language leaves little trace in the fossil record. The human language faculty can, however, be decomposed into several component abilities and a proposed evolutionary explanation of the whole must address (at least) the evolution of each of these components. Some of these features may also be found in other species, and thus permit use of the powerful comparative method. This thesis addresses the evolution of two such component features of human language; complex vocal signalling and the cultural transmission of these vocal signals. I argue that these features make a significant contribution to the nature of human language as we observe it today and so a better understanding of the evolutionary processes that gave rise to them will contribute to study of the evolution of language. This thesis addresses the evolution of these features firstly by identifying other communication systems found in nature that display them, and focusing in particular on the song of the oscine passerines (songbirds). Bird song is chosen as a model system because of the wealth of empirical data on nearly all aspects of the behaviour and the variety of song behaviour found in this group. There also appear to be some striking similarities in the development of language and song. I argue that a better understanding of the evolution of complex signalling and cultural transmission in songbirds and other species will provide useful insight into the evolution of these features in language. This thesis presents a series of related formal models that investigate several issues in the evolution of these features. I firstly present a simple formal model of bird song acquisition and use this in a computational model of evolution to investigate some ecological conditions under which vocal behaviour can become more or less reliant on cultural transmission. I then present a pertinent case study of two closely related songbird sub-species and develop a computational model that demonstrates that domestication, or a similar shift in the fitness landscape, may play a surprising role in the evolution of signal complexity (in some sense) and increased vocal plasticity. Finally, I present several models that investigate the plausibility and consistency of the ‘developmental stress hypothesis’, an important hypothesis drawn from the biological literature that proposes that song learning and song complexity may serve as a sexually selected mate quality indicator mechanism. These models provide the first theoretical support for this important but complex hypothesis and identify a number of relevant parameters that may affect the evolution of such a system.