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Phase 1: Cultural innovation and transmission: Project 009
Random copying and culture change
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Alex Bentley (Department of Archaeology & Anthropology, Bristol University)


In the social sciences there is currently no consensus on the mechanism by which cultural innovations occur, and subsequently spread. For many ideas, an appropriate model may be one analogous to random drift in population genetics: ideas are copied randomly between individuals, with original innovations (‘mutations’) occasionally appearing. In processes of pure random drift, none of variants (ideas in our case) is ‘better’ than any other, so natural selection has negligible effect compared with drift. When the numbers of different variants are tallied after some duration of a random drift process, the result is often (but not always) an elegant distribution of variant frequencies, called a power law, in which most variants are rare and a few are much more abundant. The power law means that we expect a few highly popular styles to emerge in the course of cultural evolution, just by luck rather than any inherent value. Models of random drift show good agreement with the following real-world data:

(1) Scientific journal article citations. Bentley and Maschner (2000) recently showed that ideas themselves occur in avalanches, in that one good idea inspires other ideas that in turn inspire others in a fractal pattern, like the self-similar branching of a natural river network.

(2) First names. Hahn and Bentley (2003) showed that the distributions of baby names used in the United States throughout the 20th century, for both males and females, are described by a constant power law, which is well explained by a simple drift process in which individuals randomly copy names. See news story in Nature.

(3) Neolithic pottery motifs from central Europe. Bentley and Shennan (2003) used a stochastic network growth model (similar to drift) that does remarkably well to predict the frequencies of pottery decorations over a 400-year span of prehistoric settlement in the Merzbach valley, Germany (Figure, left). From archaeologists’ common observation of “battleship curves” in stylistic evolution, this explains what governs the width (artefact frequency) or length (lifespan) of these curves.

Bentley, R.A., M.J. O'Brien, W.A. Brock (2013).
Mapping collective behavior in the big-data era.. Behavior and Brain Sciences. in press.
Bentley, R.A., P. Ormerod (2012).
Accelerated innovation and increased spatial diversity in U.S. popular culture . Advances in Complex Systems. Vol 15:1150011.
Bentley, R.A., P Ormerod, M. Batty (2011).
Evolving social influence in large populations. Behavioral Ecology and Sociobiology. Vol 65:537-546.
Bentley, R.A., P. Ormerod, S.J. Shennan (2011).
Population-level neutral model already explains linguistic patterns.. Proceedings of the Royal Society B. Vol 278:1770-1772.
Byers, B.E., K.L. Belinsky, R.A. Bentley (2010).
Independent cultural evolution of two song traditions in the chestnut-sided warbler. American Naturalist. Vol 176:476?489.
Bentley, R.A., C.P. Lipo and H.D.G. Maschner (2008).
Darwinian Archaeologies. In: R.A. Bentley, H.D.G. Maschner & C. Chippindale (eds.) (ed\s) Handbook of Archaeological Theories. Altamira Press : Lanham. 109-132.
Bentley, R. A., M.W. Hahn and S. J. Shennan (2004).
Random drift and culture change. Proceedings of the Royal Society B. Vol 271:1443-1450.
Herzog, H.A., R. A. Bentley and M. W. Hahn (2004).
Random drift and large shifts in popularity of dog breeds. Proceedings of the Royal Society B. Vol 271:S353-S356.