Detecting wholesale copying in cultural evolution

A cultural practice can spread because it is transmitted with high fidelity, but also because biased transformation leads to its reinvention. The respective effect of these two mechanisms, however, may only be quantified if we can measure and detect high-fidelity transmission. This paper proposes wholesale copying, the reproduction of a set of elements as a set, as an operational definition. Using two corpus of heraldic designs (total n = 13,453), we apply information-theoretic tools to detect cases of wholesale copying and gauge their incidence. Heraldic designs are composed according to rigorous combinatorial rules. Wholesale copying causes the frequency of a design to increase out of proportion with the frequency of the motif and tinctures that make it up. Comparing the frequency of designs with that of their component motifs and tinctures, we show that the amount of information carried by a design tracks its inheritance along family lines. A model predicting the frequency of heraldic designs based solely on the frequency of their component parts systematically outperforms one that assumes a mix of wholesale copying and random mutation (with realistic mutation rates). These findings are consistent with low but non-null incidences of wholesale copying in the diffusion of heraldic designs.