Fashion versus Reason-Then and Now
Bentley, R. Alexander, Antiquity
Analogies between modern practice and prehistoric material culture are becoming increasingly useful for archaeologists, including those interested in branding studies, for example (e.g. Wengrow, in press) and at formal research centres such as the AHRC Centre for the Evolution of Cultural Diversity and the Santa Fe Institute. Studies of modern cultural change--at a level of detail that most archaeologists can only dream about--can lead to related insights about prehistoric culture change through time. Modern fashion analysis can be methodologically similar to testing, for example, the degree to which certain prehistoric transitions reflect demographic change (e.g. Shennan 2000; Henrich 2004). How much of the Upper Palaeolithic 'revolution' in cave art is due to increases in population in western Europe? Although the data are trickier to obtain, the goal is basically the same--subtract what is considered background (e.g. population size) from what is of interest to the researcher (e.g. instances of particular art motifs). In Neolithic Germany, for example, pottery designs can be treated as the 'fashions' and numbers of longhouses are used to estimate population size (e.g. Shennan & Wilkinson 2001; Bentley & Shennan 2003).
Conceptualised this way, the study of material culture popularity can take advantage of sophisticated tools from network theory (e.g. Watts 2003) and population genetics (e.g. Cavalli-Sforza & Feldman 1981; Ammerman & Cavalli-Sforza 1984; Bentley et al. 2004). The resulting culture evolution models, in all their variety (e.g. Mesoudi et al. 2006; Shennan 2002 for reviews) can generally be divided into two camps. The first treats individuals as independent decision-makers who weigh the costs and benefits of their options, while subject to various biases of influence (e.g. Winterhalder & Smith 2000; Henrich & Gil-White 2001; Gintis 2007; McElreath & Boyd 2007). This applies well to behaviours or technology that serve some adaptive purpose, i.e. that matter to human survival, such as the conversion from foraging to farming (e.g. Renfrew 1978), or the spread of a useful technology (e.g. Rogers 1962; Henrich 2001). Even art, if it imparts some meaningful signal (e.g. mating potential), can be governed by cost/benefit decisions (e.g. Bliege Bird & Smith 2005; Geher & Miller 2007).
At the other end of the spectrum are behaviours that do not inherently 'matter', and for which there is often a large, maybe infinite, variety of options--decorative designs, musical motifs, and word forms, for example. These choices can be considered 'neutral' traits, in that what is chosen has no inherent value relative to other available options (Binford 1963; Koerper & Stickel 1980; Gillespie 1998). It assumes that whether a mother names her girl 'Jane' or 'Jamelia' depends on the current usage of the name, rather than the name itself. This is formalised as the random copying or neutral model, akin to the neutral-trait model of population genetics, for popular culture change (e.g. Neiman 1995; Lipo et al. 1997; Shennan & Wilkinson 2001; Bentley & Shennan 2003; Hahn & Bentley 2003).
Crucially, it is not proposed that people act randomly, but that the statistics of all their choices, at the population level, are comparable to random copying. It is in deliberate contrast to independent decisions--actions under random copying depend entirely on what others are doing. Applied to prehistoric studies, the model simply allows us to ask, what if everyone simply copied each other, with occasional innovation? Against this background 'canvas', more interesting phenomena become visible (e.g. Herzog et al. 2004; Eerkens & Lipo 2005). Shennan and Wilkinson (2001), for example, observed that pottery design frequencies fit neutral model predictions for the Early but not the Late Linearbandkeramik (LBK), which in turn suggests that either people were becoming more creative or they were receiving new ideas from outside communities. …