Impact of inter-individual and inter-group variation on language evolution

Languages diversity is influenced by many factors, including cultural and environmental ones, as well as variation in anatomy and physiology. While recent research has focused on variation in the vocal tract and its impact on language sound systems, it remains unclear whether this applies to other aspects of language, such as language lexicons. Therefore, the first part of this PhD research focuses on the influence of perceptual variation on language lexicons, particularly in the color domain. Specifically, we explore the hypothesis that UV incidence, through its impact on eye physiology, affects the perception of blue colors, potentially explaining why populations with high UV exposure often lack a specific term for the color blue. Two methods are employed: a cross-cultural statistical analysis and a natural (quasi-)experiment comparing color perception between participants from France and the Himba ethnic group. The findings suggest that color lexicons are shaped by a combination of environmental and cultural factors, and variation in color perception may play a role in accounting for the observed diversity. While these patterns of variation manifest at the group level, our analyses also revealed substantial variation among individuals within the same group, prompting us to ponder the extent to which language adapts to the idiosyncrasies of its speakers. Thus, the second part of this PhD aims to understand the precise mechanisms by which inter-individual variation affects language evolution. First, we conducted a laboratory experiment to study language evolution in groups of four individuals, with one participant deliberately biased. Second, we used Bayesian agent-based models to explore how a shared language emerges in heterogenous groups and how network structure contributes to language variability. The results suggest that the emergent shared language of the whole community is influenced by the language idiosyncrasies carried by a minority of biased agents, and put forward the crucial role of network structure in shaping inter-individual variation in language.Overall, this PhD research highlights that variation in languages can only be understood in the context of their cultural, biological, and physical environments and sheds light on the processes through which inter-individual and inter-group variation affect language evolution.