Abstract:One of the most well studied ecological patterns is Rapoport's rule, which posits that the geographical extent of species ranges increases at higher latitudes. However, studies to date have been limited in their geographic scope and results have been equivocal. In turn, much debate exists over potential links between Rapoport's rule and latitudinal patterns in species richness. Humans collectively speak nearly 7000 different languages, which are spread unevenly across the globe, with loci in the tropics. Cause… Show more
“…We believe that the mechanisms shaping the patterns of diversity of human languages will also be variable in their impact and context dependent. For example, patterns of species richness are strongly influenced by the overlap of ranges, but the ranges of human languages tend not to overlap in space, as we see in the Australian case presented here (Gavin & Stepp, ). Instead, the forces that determine language range sizes shape spatial patterns in language richness, with smaller ranges leading to greater richness per unit area.…”
Aim Two fundamental questions about human language demand answers: why are so many languages spoken today and why is their geographical distribution so uneven? Although hypotheses have been proposed for centuries, the processes that determine patterns of linguistic and cultural diversity remain poorly understood. Previous studies, which relied on correlative, curve-fitting approaches, have produced contradictory results. Here we present the first application of process-based simulation modelling, derived from macroecology, to examine the distribution of human groups and their languages.Location The Australian continent is used as a case study to demonstrate the power of simulation modelling for identifying processes shaping the diversity and distribution of human languages.Methods Process-based simulation models allow investigators to hold certain factors constant in order to isolate and assess the impact of modelled processes. We tested the extent to which a minimal set of processes determines the number and spatial distribution of languages on the Australian continent. Our model made three basic assumptions based on previously proposed, but untested, hypotheses: groups fill unoccupied spaces, rainfall limits population density and groups divide after reaching a maximum population.Results Remarkably, this simple model accurately predicted the total number of languages (average estimate 406, observed 407), and explained 56% of spatial variation in language richness on the Australian continent.Main conclusions Our results present strong evidence that current climatic conditions and limits to group size are important processes shaping language diversity patterns in Australia. Our study also demonstrates how simulation models from macroecology can be used to understand the processes that have shaped human cultural diversity across the globe.
“…We believe that the mechanisms shaping the patterns of diversity of human languages will also be variable in their impact and context dependent. For example, patterns of species richness are strongly influenced by the overlap of ranges, but the ranges of human languages tend not to overlap in space, as we see in the Australian case presented here (Gavin & Stepp, ). Instead, the forces that determine language range sizes shape spatial patterns in language richness, with smaller ranges leading to greater richness per unit area.…”
Aim Two fundamental questions about human language demand answers: why are so many languages spoken today and why is their geographical distribution so uneven? Although hypotheses have been proposed for centuries, the processes that determine patterns of linguistic and cultural diversity remain poorly understood. Previous studies, which relied on correlative, curve-fitting approaches, have produced contradictory results. Here we present the first application of process-based simulation modelling, derived from macroecology, to examine the distribution of human groups and their languages.Location The Australian continent is used as a case study to demonstrate the power of simulation modelling for identifying processes shaping the diversity and distribution of human languages.Methods Process-based simulation models allow investigators to hold certain factors constant in order to isolate and assess the impact of modelled processes. We tested the extent to which a minimal set of processes determines the number and spatial distribution of languages on the Australian continent. Our model made three basic assumptions based on previously proposed, but untested, hypotheses: groups fill unoccupied spaces, rainfall limits population density and groups divide after reaching a maximum population.Results Remarkably, this simple model accurately predicted the total number of languages (average estimate 406, observed 407), and explained 56% of spatial variation in language richness on the Australian continent.Main conclusions Our results present strong evidence that current climatic conditions and limits to group size are important processes shaping language diversity patterns in Australia. Our study also demonstrates how simulation models from macroecology can be used to understand the processes that have shaped human cultural diversity across the globe.
“…Yet, there are broad geographic patterns in the distribution of languages, suggesting a strong role for environmental determination of language diversity. The most notable of these patterns are latitudinal gradients: language diversity increases towards the equator 4â11 , and languages in the tropics tend to be restricted to smaller areas than languages at higher latitudes 4,6,8 .Fig. 1Global distribution of language diversity.…”
Language diversity is distributed unevenly over the globe. Intriguingly, patterns of language diversity resemble biodiversity patterns, leading to suggestions that similar mechanisms may underlie both linguistic and biological diversification. Here we present the first global analysis of language diversity that compares the relative importance of two key ecological mechanisms â isolation and ecological risk â after correcting for spatial autocorrelation and phylogenetic non-independence. We find significant effects of climate on language diversity, consistent with the ecological risk hypothesis that areas of high year-round productivity lead to more languages by supporting human cultural groups with smaller distributions. Climate has a much stronger effect on language diversity than landscape features, such as altitudinal range and river density, which might contribute to isolation of cultural groups. The association between biodiversity and language diversity appears to be an incidental effect of their covariation with climate, rather than a causal link between the two.
“…To distinguish between the three scenarios we treated spatial proximity and inheritance as potential confounds and carried out a partial RDA to control their effect (Supplementary Information). As societies and languages placed far from the equator tend to display larger spatial ranges( 58 ), we represented the territory of each society with areas rather than points and sample random spatial locations from within these areas. The partial RDA reveals strong evidence against the recent contact scenario: spatial proximity fails to explain both associations (Fig.…”
Culture evolves in ways that are analogous to, but distinct from, genetic evolution. Previous studies have demonstrated correlations between genetic and cultural diversity at small scales within language families, but few studies have empirically investigated parallels between genetic and cultural evolution across multiple language families using a diverse range of cultural data. Here we report an analysis comparing cultural and genetic data from 13 populations from in and around Northeast Asia spanning 10 different language families/isolates. We construct distance matrices for language (grammar, phonology, lexicon), music (song structure, performance style), and genomes (genome-wide SNPs) and test for correlations among them. After controlling for spatial autocorrelation and recent contact, robust correlations emerge between genetic and grammatical distances. Our results suggest that grammatical structure might be one of the strongest cultural indicators of human population history, while also demonstrating differences among cultural and genetic relationships that highlight the complex nature of human cultural and genetic evolution.
Significance StatementComparing cultural traits to the genetic relationships of populations can reveal the extent to which cultural diversification reflects population history. To date, this approach has been mostly used to compare genetic relationships with the linguistic relationships that hold within language families, thereby limiting time depth to considerably less than 10,000 years. Here, we compare the genetic relationships of 13 populations in and around Northeast Asia to linguistic and musical relationships spanning different language families, thereby probing potential effects of population history at deeper time depths. We find that after controlling for geography, similarities in grammatical relationships reflect genetic relationships, suggesting that grammatical structure captures deep-time population history.
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