Words and bones. Combining linguistic and phenotypic data to probe deep history

Reconstructing the deep history of human diversity draws on combined evidence from linguistics, genetics and biological anthropology. Early explorations on the association between languages and genes suggested that patterns of linguistic diversity paralleled those of genetic diversity. Most of these early studies used pairwise distance measures of genetic and linguistic dissimilarity to statistically compare the significance of their association (Derish and Sokal 1988 and much subsequent work). Other work on the phylogenetic structure of genetic and linguistic data assessed similarities in the topology of generated trees (Cavalli-Sforza et al. 1988; 1992). The general conclusion drawn from this body of work was that when human populations separated and became genetically differentiated, their languages followed a similar evolutionary pattern.

Recent work using quantitative measures of linguistic diversity (Creanza et al, 2015; Longobardi et al., 2015, among others) largely confirm the gene-language correlation.

Likewise, skeletal morphology has been shown to be correlated with genetic signals (Harvati and Weaver 2006, among others). However, some anatomical regions are better suited for this type of analysis than others: the shape of the neurocranium (brain case) and cranial base, as measured either by 3-D geometric morphometric data or by conventional linear measurements, appear to track population history relatively closely. The face, on the other hand, was found to respond to selection pressures caused by environmental factors such as climate or subsistence patterns.

In an ongoing study, we compared phenotypic distances related to different aspects of cranial morphology to linguistic distances. The latter were derived from word lists from the Automatic Similarity Judgment Program (Wichman et al., 2013). The study used cranial data from ca. 150 populations around the world. Quite surprisingly, we found that linguistic distances show a stronger and more robust correlation with the face than with the neurocranium. This suggests that linguistic diversity cannot adequately be explained by population diversification alone.

In the talk I will deploy phylogenetic comparative methods combined with causal inference --- especially path equation modeling --- to disentangle the vertical and horizontal processes governing phenotypic and linguistic diversity and their causal structure.