Two new Greenhill Papers

Simon Greenhill has just announced two new papers on applying phylogenetic techniques to the study of culture. No doubt I’ll be blogging about these at some point in the future. Below are the abstracts:

Currie TE, Greenhill SJ, & Mace R (in press). Is horizontal transmission really a problem for phylogenetic comparative methods? A simulation study using continuous cultural traits. Philosophical Transactions of the Royal Society, B:

Phylogenetic comparative methods (PCMs) provide a potentially powerful toolkit for testing hypotheses about cultural evolution. Here we build on previous simulation work by Nunn et al. (2006) to assess the effect horizontal transmission between cultures has on the ability of both phylogenetic and non-phylogenetic methods to make inferences about trait evolution.

We found that the mode of horizontal transmission of traits has important consequences for both methods. Where traits were horizontally transmitted separately PCMs accurately reported when trait evolution was not correlated even at the highest levels of horizontal transmission.

In contrast, linear regression analyses often incorrectly concluded that traits were correlated. Where simulated trait evolution was not correlated and traits were horizontally transmitted as a pair both methods showed increased levels of positive correlation with increasing horizontal transmission.

Where simulated trait evolution was correlated increasing rates of separate horizontal transmission led to decreasing levels of correlation for both methods, but that increasing rates of paired horizontal transmission did not. Furthermore, the PCM was also able to make accurate inferences about the ancestral state of traits.

These results suggest that under certain conditions PCMs can be robust to the effects of horizontal transmission. We discuss ways that future work can investigate the mode and tempo of horizontal transmission of cultural traits.

 Gray RD, Bryant D, & Greenhill SJ (in press) On the shape and fabric of human history. Philosophical Transactions of the Royal Society, B:

In this paper we outline two debates about the nature of human cultural history. The first focuses on the extent to which human history is treelike (its shape), and the second on the unity of that history (its fabric).

Proponents of cultural phylogenetics are often accused of assuming that human history has been both highly tree-like and consists of tightly linked lineages. Critics have pointed out obvious exceptions to these assumptions.

Instead of a priori dichotomous disputes about the validity of cultural phylogenetics phylogenies, we suggest that the debate is better conceptualized as involving positions along continuous dimensions. The challenge for empirical research is therefore to determine where particular aspects of culture lie on these dimensions.

We discuss the ability of current computational methods derived from evolutionary biology to address these questions. These methods are then used to compare the extent to which lexical evolution is treelike in different parts of the world and to evaluate the coherence of cultural and linguistic lineages.

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