Phase 2: Theme C - Innovations in complex social networks: Project C010|
Measuring Cultural Selection
Stephen Shennan (Institute of Archaeology, University College London)
Mark Thomas (Research Department of Genetics, Evolution and Environment, University College London)
Mark Collard (Department of Archaeology, Simon Fraser University)
A key strand of previous work at the AHRC Centre was the development of neutral models of cultural change, which has in some cases enabled the inference of empirical innovation rates (e.g. baby names, ceramic decorative style, patent rates). However, the quantitative measurement of departures from neutrality and their statistical significance remains weak, so that results remain open to question. We will be developing previous work by using techniques from population genetics to define frequency-based measures of cultural diversity in a trait system with selection. We will also be deriving measures of selection strength, based on the time course to fixation of a selectively advantageous trait where population size and error rate is known (by analogy with Fay & Wu’s  H statistic and Tajima’s  D statistic, both from genetics). Special attention to effects of population size on the retention of diversity, and the effects of small population size on the probability of stochastic loss of an advantageous cultural innovation will also be considered.
FINAL PROJECT REPORT:
This project was initially started with Dr Elise Bell as PDRF but her topic was changed and it has continued to be pursued by others, mainly by Adam Powell in his PhD, which is now complete. One publication arising from our work in this area, focussing on the role of population size in the accumulation of culture, has already appeared in Science. We will now be producing further papers arising from the thesis. These will include the follow up to the paper by Lycett and Mesoudi on distinguishing drift and conformity using a power law approach, together with Alex Bentley; this was almost complete a year ago but work stopped so that Adam could focus on completing his thesis. They will also include a paper describing a new method using Approximate Bayesian Computation methods to estimate the parameters of drift models. In addition Anne Kandler has worked with Shennan to develop a method for using diversity measures to evaluate the role of drift that is statistically rigorous but does not require the standard assumptions of constant population size and innovation rate. This will shortly lead to a publication.
Recent years have seen increasing interest in the role of population size in affecting the accumulation of culture and also in the role of drift models. For example, Stauffer has developed Shennan’s original ‘drift load’ model of cultural accumulation to take account of fluctuating environments and work has been carried out using empirical data to test for the effect of population size on cultural complexity in Polynesia (Kline and Boyd 2010). In the Centre Mark Lake and Enrico Crema are now taking such work in new directions (paper presented at CECD conference September 2010).
Drift models and identifying their role and significance have become a major topic of interest in recent years, with important work by Lipo and Eerkens, Buchanan and Hamilton and by Brantingham, as well as the work by Mesoudi and Lycett noted above. As with the population models, the CECD has continued to be at the forefront of these developments, with the work by Steele et al on Hittite bowls arising from another of the Centre projects, and the work by Powell, Kandler et al under the broad heading of this project outlined above.
Work on these two topics has recently been the subject of a review (Shennan accepted).
|•||Shennan, S.J (2011).|
Descent with modification and the archaeological record. Philosophical Transactions of the Royal Society B. Vol 366:1070-1079 .
|•||Powell, A., S.J. Shennan and M.G. Thomas (2009).|
Late Pleistocene Demography and the Appearance of Modern Human Behavior. Science. Vol 324:1298-1301.