Assessing the relative impact of historical divergence and inter-group transmission on cultural patterns: a method from evolutionary ecology

Cultural transmission of traditional songs in the Ryukyu Archipelago

Geographic patterns of cultural variations are affected by how cultural traits are transmitted within and between populations. It has been argued that cultural traits are transmitted in different manners depending on their characteristics; for example, words for basic concepts are less liable to horizontal transmission between populations (i.e., borrowing) than other words. Here we examine the geographic variation of traditional songs in the Ryukyu Archipelago, southwestern islands of Japan, to explore cultural evolution of music with a focus on different social contexts in which songs are sung. Published scores of 1,342 traditional songs are coded using the CantoCore song classification scheme and distances between the songs are calculated from the codings. Neighbor-Net graphs of regions/islands are generated on the basis of the musical distances, and delta scores are obtained to examine the treelikeness of the networks. We also perform analysis of molecular variance (AMOVA) to evaluate the extent of musical diversification among regions/islands. Our results suggest that horizontal transmission between populations has played a greater role in the formation of musical diversity than that of linguistic diversity in the Ryukyu Archipelago and that the social context in which songs are sung has an effect on how they are transmitted within and between populations. In addition, we compare the observed patterns of song diversity among regions/islands with those of lexical and mitochondrial-DNA (mtDNA) diversity, showing that the variation of songs sung in the "work" context are associated with the linguistic variation, whereas no association is found between the musical and genetic variation.

The potential to infer the historical pattern of cultural macroevolution

Phylogenetic analyses increasingly take centre-stage in our understanding of the processes shaping patterns of cultural diversity and cultural evolution over time. Just as biologists explain the origins and maintenance of trait differences among organisms using phylogenetic methods, so anthropologists studying cultural macroevolutionary processes use phylogenetic methods to uncover the history of human populations and the dynamics of culturally transmitted traits. In this paper, we revisit concerns with the validity of these methods. Specifically, we use simulations to reveal how properties of the sample (size, missing data), properties of the tree (shape) and properties of the traits (rate of change, number of variants, transmission mode) might influence the inferences that can be drawn about trait distributions across a given phylogeny and the power to discern alternative histories. Our approach shows that in two example datasets specific combinations of properties of the sample, of the tree and of the trait can lead to potentially high rates of Type I and Type II errors. We offer this simulation tool to help assess the potential impact of this list of persistent perils in future cultural macroevolutionary work. This article is part of the theme issue 'Foundations of cultural evolution'.

Tangsa and Wancho of North-East India Use Animals not only as Food and Medicine but also as Additional Cultural Attributes

Cultural and ritual uses of animals beyond those for food and medicine should not be dismissed if we wish to understand the pressure that wildlife is under. We documented such uses for the Tangsa and Wancho tribals of Eastern Arunachal Pradesh (India). Group discussions with assembled members of 10 accessible villages in each of the tribal areas were carried out in 2015 and 2016. Vernacular names of culturally important species were noted and details of hunting practices were recorded. The different uses of animals and their parts during rituals and festivals and their significance in decorations and adornments, in supernatural beliefs and in connection with tribal folklore (stories) are documented. Folklore helps us understand why some species are hunted and consumed while others for no apparent reason are killed or simply ignored. Similarities as well as differences between the two tribes were recorded and possible reasons for the differences are given. The roles that the government as well as the tribal leaders play to halt or slow down the erosion and gradual disappearance of traditions that define the two cultures without losing already rare and endangered species are highlighted.

The popularity spectrum applied to a cross-cultural question

We investigate a new approach for identifying the contribution of horizontal transmission between groups to cross-cultural similarity. This method can be applied to datasets that record the presence or absence of artefacts, or attributes thereof, in archaeological and ethnographic assemblages, from which popularity spectra can be constructed. Based on analytical and simulation models, we show that the form of such spectra is sensitive to horizontal transmission between groups. We then fit the analytical model to existing datasets by Bayesian MCMC and obtain evidence for strong horizontal transmission in oceanic as opposed to continental datasets. We check the validity of our statistical method by using individual-based models, and show that the vertical transmission rate tends to be underestimated if the datasets are obtained from lattice-structured rather than island-structured meta-populations. We also suggest that there may be more borrowing of functional than stylistic traits, although the evidence for this is currently ambiguous.