The Pace of Cultural Evolution
Biological rates (black circles) and cultural rates (gray squares), calculated as change per generation, are inversely correlated to the interval of the time over which the rates are measured. The solid lines represent the linear mixed model of interaction that best fit the biological (black line) and cultural (gray line) distributions (Table 5). The conversion of rates from an absolute time scale to a generational time scale impacts mostly the biological rates from species with a short generation time. For any given amount of phenotypic change observed over any given time interval, the difference between rate of change per millions of years and rates of change per generation time increases as generation time of species increases. This effect explains why the difference between the slopes of the two linear models, although significant, is smaller (Table 5) than that shown in Figure 2.